/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtQuick module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
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** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL3 included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 3 requirements
** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or (at your option) the GNU General
** Public license version 3 or any later version approved by the KDE Free
** Qt Foundation. The licenses are as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
** included in the packaging of this file. Please review the following
** information to ensure the GNU General Public License requirements will
** be met: https://www.gnu.org/licenses/gpl-2.0.html and
** https://www.gnu.org/licenses/gpl-3.0.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "qquickitemview_p_p.h"
#include "qquickitemviewfxitem_p_p.h"
#include <QtQuick/private/qquicktransition_p.h>
#include <QtQml/QQmlInfo>
#include "qplatformdefs.h"

QT_BEGIN_NAMESPACE

Q_LOGGING_CATEGORY(lcItemViewDelegateLifecycle, "qt.quick.itemview.lifecycle")

// Default cacheBuffer for all views.
#ifndef QML_VIEW_DEFAULTCACHEBUFFER
#define QML_VIEW_DEFAULTCACHEBUFFER 320
#endif

FxViewItem::FxViewItem(QQuickItem *i, QQuickItemView *v, bool own, QQuickItemViewAttached *attached)
    : QQuickItemViewFxItem(i, own, QQuickItemViewPrivate::get(v))
    , view(v)
    , attached(attached)
{
    if (attached) // can be null for default components (see createComponentItem)
        attached->setView(view);
}

QQuickItemViewChangeSet::QQuickItemViewChangeSet()
    : active(false)
{
    reset();
}

bool QQuickItemViewChangeSet::hasPendingChanges() const
{
    return !pendingChanges.isEmpty();
}

void QQuickItemViewChangeSet::applyChanges(const QQmlChangeSet &changeSet)
{
    pendingChanges.apply(changeSet);

    int moveId = -1;
    int moveOffset = 0;

    for (const QQmlChangeSet::Change &r : changeSet.removes()) {
        itemCount -= r.count;
        if (moveId == -1 && newCurrentIndex >= r.index + r.count) {
            newCurrentIndex -= r.count;
            currentChanged = true;
        } else if (moveId == -1 && newCurrentIndex >= r.index && newCurrentIndex < r.index + r.count) {
            // current item has been removed.
            if (r.isMove()) {
                moveId = r.moveId;
                moveOffset = newCurrentIndex - r.index;
            } else {
                currentRemoved = true;
                newCurrentIndex = -1;
                if (itemCount)
                    newCurrentIndex = qMin(r.index, itemCount - 1);
            }
            currentChanged = true;
        }
    }
    for (const QQmlChangeSet::Change &i : changeSet.inserts()) {
        if (moveId == -1) {
            if (itemCount && newCurrentIndex >= i.index) {
                newCurrentIndex += i.count;
                currentChanged = true;
            } else if (newCurrentIndex < 0) {
                newCurrentIndex = 0;
                currentChanged = true;
            } else if (newCurrentIndex == 0 && !itemCount) {
                // this is the first item, set the initial current index
                currentChanged = true;
            }
        } else if (moveId == i.moveId) {
            newCurrentIndex = i.index + moveOffset;
        }
        itemCount += i.count;
    }
}

void QQuickItemViewChangeSet::applyBufferedChanges(const QQuickItemViewChangeSet &other)
{
    if (!other.hasPendingChanges())
        return;

    pendingChanges.apply(other.pendingChanges);
    itemCount = other.itemCount;
    newCurrentIndex = other.newCurrentIndex;
    currentChanged = other.currentChanged;
    currentRemoved = other.currentRemoved;
}

void QQuickItemViewChangeSet::prepare(int currentIndex, int count)
{
    if (active)
        return;
    reset();
    active = true;
    itemCount = count;
    newCurrentIndex = currentIndex;
}

void QQuickItemViewChangeSet::reset()
{
    itemCount = 0;
    newCurrentIndex = -1;
    pendingChanges.clear();
    removedItems.clear();
    active = false;
    currentChanged = false;
    currentRemoved = false;
}

//-----------------------------------

QQuickItemView::QQuickItemView(QQuickFlickablePrivate &dd, QQuickItem *parent)
    : QQuickFlickable(dd, parent)
{
    Q_D(QQuickItemView);
    d->init();
}

QQuickItemView::~QQuickItemView()
{
    Q_D(QQuickItemView);
    d->clear(true);
    if (d->ownModel)
        delete d->model;
    delete d->header;
    delete d->footer;
}


QQuickItem *QQuickItemView::currentItem() const
{
    Q_D(const QQuickItemView);
    return d->currentItem ? d->currentItem->item : nullptr;
}

QVariant QQuickItemView::model() const
{
    Q_D(const QQuickItemView);
    return d->modelVariant;
}

void QQuickItemView::setModel(const QVariant &m)
{
    Q_D(QQuickItemView);
    QVariant model = m;
    if (model.userType() == qMetaTypeId<QJSValue>())
        model = model.value<QJSValue>().toVariant();

    if (d->modelVariant == model)
        return;
    if (d->model) {
        disconnect(d->model, SIGNAL(modelUpdated(QQmlChangeSet,bool)),
                this, SLOT(modelUpdated(QQmlChangeSet,bool)));
        disconnect(d->model, SIGNAL(initItem(int,QObject*)), this, SLOT(initItem(int,QObject*)));
        disconnect(d->model, SIGNAL(createdItem(int,QObject*)), this, SLOT(createdItem(int,QObject*)));
        disconnect(d->model, SIGNAL(destroyingItem(QObject*)), this, SLOT(destroyingItem(QObject*)));
        if (QQmlDelegateModel *delegateModel = qobject_cast<QQmlDelegateModel*>(d->model)) {
            disconnect(delegateModel, SIGNAL(itemPooled(int, QObject *)), this, SLOT(onItemPooled(int, QObject *)));
            disconnect(delegateModel, SIGNAL(itemReused(int, QObject *)), this, SLOT(onItemReused(int, QObject *)));
        }
    }

    QQmlInstanceModel *oldModel = d->model;

    d->clear();
    d->model = nullptr;
    d->setPosition(d->contentStartOffset());
    d->modelVariant = model;

    QObject *object = qvariant_cast<QObject*>(model);
    QQmlInstanceModel *vim = nullptr;
    if (object && (vim = qobject_cast<QQmlInstanceModel *>(object))) {
        if (d->ownModel) {
            delete oldModel;
            d->ownModel = false;
        }
        d->model = vim;
    } else {
        if (!d->ownModel) {
            d->model = new QQmlDelegateModel(qmlContext(this), this);
            d->ownModel = true;
            if (isComponentComplete())
                static_cast<QQmlDelegateModel *>(d->model.data())->componentComplete();
        } else {
            d->model = oldModel;
        }
        if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model))
            dataModel->setModel(model);
    }

    if (d->model) {
        d->bufferMode = QQuickItemViewPrivate::BufferBefore | QQuickItemViewPrivate::BufferAfter;
        connect(d->model, SIGNAL(createdItem(int,QObject*)), this, SLOT(createdItem(int,QObject*)));
        connect(d->model, SIGNAL(initItem(int,QObject*)), this, SLOT(initItem(int,QObject*)));
        connect(d->model, SIGNAL(destroyingItem(QObject*)), this, SLOT(destroyingItem(QObject*)));
        if (QQmlDelegateModel *delegateModel = qobject_cast<QQmlDelegateModel*>(d->model)) {
            connect(delegateModel, SIGNAL(itemPooled(int, QObject *)), this, SLOT(onItemPooled(int, QObject *)));
            connect(delegateModel, SIGNAL(itemReused(int, QObject *)), this, SLOT(onItemReused(int, QObject *)));
        }
        if (isComponentComplete()) {
            d->updateSectionCriteria();
            d->refill();
            /* Setting currentIndex to -2 ensures that we always enter the "currentIndex changed"
               code path in setCurrentIndex, updating bindings depending on currentIndex.*/
            d->currentIndex = -2;
            setCurrentIndex(d->model->count() > 0 ? 0 : -1);
            d->updateViewport();

            if (d->transitioner && d->transitioner->populateTransition) {
                d->transitioner->setPopulateTransitionEnabled(true);
                d->forceLayoutPolish();
            }
        }

        connect(d->model, SIGNAL(modelUpdated(QQmlChangeSet,bool)),
                this, SLOT(modelUpdated(QQmlChangeSet,bool)));
        if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model))
            QObjectPrivate::connect(dataModel, &QQmlDelegateModel::delegateChanged, d, &QQuickItemViewPrivate::applyDelegateChange);
        emit countChanged();
    }
    emit modelChanged();
    d->moveReason = QQuickItemViewPrivate::Other;
}

QQmlComponent *QQuickItemView::delegate() const
{
    Q_D(const QQuickItemView);
    if (d->model) {
        if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model))
            return dataModel->delegate();
    }

    return nullptr;
}

void QQuickItemView::setDelegate(QQmlComponent *delegate)
{
    Q_D(QQuickItemView);
    if (delegate == this->delegate())
        return;
    if (!d->ownModel) {
        d->model = new QQmlDelegateModel(qmlContext(this));
        d->ownModel = true;
        if (isComponentComplete())
            static_cast<QQmlDelegateModel *>(d->model.data())->componentComplete();
    }
    if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model)) {
        int oldCount = dataModel->count();
        dataModel->setDelegate(delegate);
        if (oldCount != dataModel->count())
            emit countChanged();
    }
    emit delegateChanged();
    d->delegateValidated = false;
}


int QQuickItemView::count() const
{
    Q_D(const QQuickItemView);
    if (!d->model)
        return 0;
    return d->model->count();
}

int QQuickItemView::currentIndex() const
{
    Q_D(const QQuickItemView);
    return d->currentIndex;
}

void QQuickItemView::setCurrentIndex(int index)
{
    Q_D(QQuickItemView);
    if (d->inRequest)  // currently creating item
        return;
    d->currentIndexCleared = (index == -1);

    d->applyPendingChanges();
    if (index == d->currentIndex)
        return;
    if (isComponentComplete() && d->isValid()) {
        d->moveReason = QQuickItemViewPrivate::SetIndex;
        d->updateCurrent(index);
    } else if (d->currentIndex != index) {
        d->currentIndex = index;
        emit currentIndexChanged();
    }
}


bool QQuickItemView::isWrapEnabled() const
{
    Q_D(const QQuickItemView);
    return d->wrap;
}

void QQuickItemView::setWrapEnabled(bool wrap)
{
    Q_D(QQuickItemView);
    if (d->wrap == wrap)
        return;
    d->wrap = wrap;
    emit keyNavigationWrapsChanged();
}

bool QQuickItemView::isKeyNavigationEnabled() const
{
    Q_D(const QQuickItemView);
    return d->explicitKeyNavigationEnabled ? d->keyNavigationEnabled : d->interactive;
}

void QQuickItemView::setKeyNavigationEnabled(bool keyNavigationEnabled)
{
    // TODO: default binding to "interactive" can be removed in Qt 6; it only exists for compatibility reasons.
    Q_D(QQuickItemView);
    const bool wasImplicit = !d->explicitKeyNavigationEnabled;
    if (wasImplicit)
        QObject::disconnect(this, &QQuickFlickable::interactiveChanged, this, &QQuickItemView::keyNavigationEnabledChanged);

    d->explicitKeyNavigationEnabled = true;

    // Ensure that we emit the change signal in case there is no different in value.
    if (d->keyNavigationEnabled != keyNavigationEnabled || wasImplicit) {
        d->keyNavigationEnabled = keyNavigationEnabled;
        emit keyNavigationEnabledChanged();
    }
}

int QQuickItemView::cacheBuffer() const
{
    Q_D(const QQuickItemView);
    return d->buffer;
}

void QQuickItemView::setCacheBuffer(int b)
{
    Q_D(QQuickItemView);
    if (b < 0) {
        qmlWarning(this) << "Cannot set a negative cache buffer";
        return;
    }

    if (d->buffer != b) {
        d->buffer = b;
        if (isComponentComplete()) {
            d->bufferMode = QQuickItemViewPrivate::BufferBefore | QQuickItemViewPrivate::BufferAfter;
            d->refillOrLayout();
        }
        emit cacheBufferChanged();
    }
}

int QQuickItemView::displayMarginBeginning() const
{
    Q_D(const QQuickItemView);
    return d->displayMarginBeginning;
}

void QQuickItemView::setDisplayMarginBeginning(int margin)
{
    Q_D(QQuickItemView);
    if (d->displayMarginBeginning != margin) {
        d->displayMarginBeginning = margin;
        if (isComponentComplete()) {
            d->forceLayoutPolish();
        }
        emit displayMarginBeginningChanged();
    }
}

int QQuickItemView::displayMarginEnd() const
{
    Q_D(const QQuickItemView);
    return d->displayMarginEnd;
}

void QQuickItemView::setDisplayMarginEnd(int margin)
{
    Q_D(QQuickItemView);
    if (d->displayMarginEnd != margin) {
        d->displayMarginEnd = margin;
        if (isComponentComplete()) {
            d->forceLayoutPolish();
        }
        emit displayMarginEndChanged();
    }
}

Qt::LayoutDirection QQuickItemView::layoutDirection() const
{
    Q_D(const QQuickItemView);
    return d->layoutDirection;
}

void QQuickItemView::setLayoutDirection(Qt::LayoutDirection layoutDirection)
{
    Q_D(QQuickItemView);
    if (d->layoutDirection != layoutDirection) {
        d->layoutDirection = layoutDirection;
        d->regenerate();
        emit layoutDirectionChanged();
        emit effectiveLayoutDirectionChanged();
    }
}

Qt::LayoutDirection QQuickItemView::effectiveLayoutDirection() const
{
    Q_D(const QQuickItemView);
    if (d->effectiveLayoutMirror)
        return d->layoutDirection == Qt::RightToLeft ? Qt::LeftToRight : Qt::RightToLeft;
    else
        return d->layoutDirection;
}

QQuickItemView::VerticalLayoutDirection QQuickItemView::verticalLayoutDirection() const
{
    Q_D(const QQuickItemView);
    return d->verticalLayoutDirection;
}

void QQuickItemView::setVerticalLayoutDirection(VerticalLayoutDirection layoutDirection)
{
    Q_D(QQuickItemView);
    if (d->verticalLayoutDirection != layoutDirection) {
        d->verticalLayoutDirection = layoutDirection;
        d->regenerate();
        emit verticalLayoutDirectionChanged();
    }
}

QQmlComponent *QQuickItemView::header() const
{
    Q_D(const QQuickItemView);
    return d->headerComponent;
}

QQuickItem *QQuickItemView::headerItem() const
{
    Q_D(const QQuickItemView);
    return d->header ? d->header->item : nullptr;
}

void QQuickItemView::setHeader(QQmlComponent *headerComponent)
{
    Q_D(QQuickItemView);
    if (d->headerComponent != headerComponent) {
        d->applyPendingChanges();
        delete d->header;
        d->header = nullptr;
        d->headerComponent = headerComponent;

        d->markExtentsDirty();

        if (isComponentComplete()) {
            d->updateHeader();
            d->updateFooter();
            d->updateViewport();
            d->fixupPosition();
        } else {
            emit headerItemChanged();
        }
        emit headerChanged();
    }
}

QQmlComponent *QQuickItemView::footer() const
{
    Q_D(const QQuickItemView);
    return d->footerComponent;
}

QQuickItem *QQuickItemView::footerItem() const
{
    Q_D(const QQuickItemView);
    return d->footer ? d->footer->item : nullptr;
}

void QQuickItemView::setFooter(QQmlComponent *footerComponent)
{
    Q_D(QQuickItemView);
    if (d->footerComponent != footerComponent) {
        d->applyPendingChanges();
        delete d->footer;
        d->footer = nullptr;
        d->footerComponent = footerComponent;

        if (isComponentComplete()) {
            d->updateFooter();
            d->updateViewport();
            d->fixupPosition();
        } else {
            emit footerItemChanged();
        }
        emit footerChanged();
    }
}

QQmlComponent *QQuickItemView::highlight() const
{
    Q_D(const QQuickItemView);
    return d->highlightComponent;
}

void QQuickItemView::setHighlight(QQmlComponent *highlightComponent)
{
    Q_D(QQuickItemView);
    if (highlightComponent != d->highlightComponent) {
        d->applyPendingChanges();
        d->highlightComponent = highlightComponent;
        d->createHighlight();
        if (d->currentItem)
            d->updateHighlight();
        emit highlightChanged();
    }
}

QQuickItem *QQuickItemView::highlightItem() const
{
    Q_D(const QQuickItemView);
    return d->highlight ? d->highlight->item : nullptr;
}

bool QQuickItemView::highlightFollowsCurrentItem() const
{
    Q_D(const QQuickItemView);
    return d->autoHighlight;
}

void QQuickItemView::setHighlightFollowsCurrentItem(bool autoHighlight)
{
    Q_D(QQuickItemView);
    if (d->autoHighlight != autoHighlight) {
        d->autoHighlight = autoHighlight;
        if (autoHighlight)
            d->updateHighlight();
        emit highlightFollowsCurrentItemChanged();
    }
}

QQuickItemView::HighlightRangeMode QQuickItemView::highlightRangeMode() const
{
    Q_D(const QQuickItemView);
    return static_cast<QQuickItemView::HighlightRangeMode>(d->highlightRange);
}

void QQuickItemView::setHighlightRangeMode(HighlightRangeMode mode)
{
    Q_D(QQuickItemView);
    if (d->highlightRange == mode)
        return;
    d->highlightRange = mode;
    d->haveHighlightRange = d->highlightRange != NoHighlightRange && d->highlightRangeStart <= d->highlightRangeEnd;
    if (isComponentComplete()) {
        d->updateViewport();
        d->moveReason = QQuickItemViewPrivate::Other;
        d->fixupPosition();
    }
    emit highlightRangeModeChanged();
}

//###Possibly rename these properties, since they are very useful even without a highlight?
qreal QQuickItemView::preferredHighlightBegin() const
{
    Q_D(const QQuickItemView);
    return d->highlightRangeStart;
}

void QQuickItemView::setPreferredHighlightBegin(qreal start)
{
    Q_D(QQuickItemView);
    d->highlightRangeStartValid = true;
    if (d->highlightRangeStart == start)
        return;
    d->highlightRangeStart = start;
    d->haveHighlightRange = d->highlightRange != NoHighlightRange && d->highlightRangeStart <= d->highlightRangeEnd;
    if (isComponentComplete()) {
        d->updateViewport();
        if (!isMoving() && !isFlicking()) {
            d->moveReason = QQuickItemViewPrivate::Other;
            d->fixupPosition();
        }
    }
    emit preferredHighlightBeginChanged();
}

void QQuickItemView::resetPreferredHighlightBegin()
{
    Q_D(QQuickItemView);
    d->highlightRangeStartValid = false;
    if (d->highlightRangeStart == 0)
        return;
    d->highlightRangeStart = 0;
    if (isComponentComplete()) {
        d->updateViewport();
        if (!isMoving() && !isFlicking()) {
            d->moveReason = QQuickItemViewPrivate::Other;
            d->fixupPosition();
        }
    }
    emit preferredHighlightBeginChanged();
}

qreal QQuickItemView::preferredHighlightEnd() const
{
    Q_D(const QQuickItemView);
    return d->highlightRangeEnd;
}

void QQuickItemView::setPreferredHighlightEnd(qreal end)
{
    Q_D(QQuickItemView);
    d->highlightRangeEndValid = true;
    if (d->highlightRangeEnd == end)
        return;
    d->highlightRangeEnd = end;
    d->haveHighlightRange = d->highlightRange != NoHighlightRange && d->highlightRangeStart <= d->highlightRangeEnd;
    if (isComponentComplete()) {
        d->updateViewport();
        if (!isMoving() && !isFlicking()) {
            d->moveReason = QQuickItemViewPrivate::Other;
            d->fixupPosition();
        }
    }
    emit preferredHighlightEndChanged();
}

void QQuickItemView::resetPreferredHighlightEnd()
{
    Q_D(QQuickItemView);
    d->highlightRangeEndValid = false;
    if (d->highlightRangeEnd == 0)
        return;
    d->highlightRangeEnd = 0;
    if (isComponentComplete()) {
        d->updateViewport();
        if (!isMoving() && !isFlicking()) {
            d->moveReason = QQuickItemViewPrivate::Other;
            d->fixupPosition();
        }
    }
    emit preferredHighlightEndChanged();
}

int QQuickItemView::highlightMoveDuration() const
{
    Q_D(const QQuickItemView);
    return d->highlightMoveDuration;
}

void QQuickItemView::setHighlightMoveDuration(int duration)
{
    Q_D(QQuickItemView);
    if (d->highlightMoveDuration != duration) {
        d->highlightMoveDuration = duration;
        emit highlightMoveDurationChanged();
    }
}

bool QQuickItemView::reuseItems() const
{
    return bool(d_func()->reusableFlag == QQmlDelegateModel::Reusable);
}

void QQuickItemView::setReuseItems(bool reuse)
{
    Q_D(QQuickItemView);
    if (reuseItems() == reuse)
        return;

    d->reusableFlag = reuse ? QQmlDelegateModel::Reusable : QQmlDelegateModel::NotReusable;

    if (!reuse && d->model) {
        // When we're told to not reuse items, we
        // immediately, as documented, drain the pool.
        d->model->drainReusableItemsPool(0);
    }

    emit reuseItemsChanged();
}

QQuickTransition *QQuickItemView::populateTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->populateTransition : nullptr;
}

void QQuickItemView::setPopulateTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->populateTransition != transition) {
        d->transitioner->populateTransition = transition;
        emit populateTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::addTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->addTransition : nullptr;
}

void QQuickItemView::setAddTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->addTransition != transition) {
        d->transitioner->addTransition = transition;
        emit addTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::addDisplacedTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->addDisplacedTransition : nullptr;
}

void QQuickItemView::setAddDisplacedTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->addDisplacedTransition != transition) {
        d->transitioner->addDisplacedTransition = transition;
        emit addDisplacedTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::moveTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->moveTransition : nullptr;
}

void QQuickItemView::setMoveTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->moveTransition != transition) {
        d->transitioner->moveTransition = transition;
        emit moveTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::moveDisplacedTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->moveDisplacedTransition : nullptr;
}

void QQuickItemView::setMoveDisplacedTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->moveDisplacedTransition != transition) {
        d->transitioner->moveDisplacedTransition = transition;
        emit moveDisplacedTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::removeTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->removeTransition : nullptr;
}

void QQuickItemView::setRemoveTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->removeTransition != transition) {
        d->transitioner->removeTransition = transition;
        emit removeTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::removeDisplacedTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->removeDisplacedTransition : nullptr;
}

void QQuickItemView::setRemoveDisplacedTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->removeDisplacedTransition != transition) {
        d->transitioner->removeDisplacedTransition = transition;
        emit removeDisplacedTransitionChanged();
    }
}

QQuickTransition *QQuickItemView::displacedTransition() const
{
    Q_D(const QQuickItemView);
    return d->transitioner ? d->transitioner->displacedTransition : nullptr;
}

void QQuickItemView::setDisplacedTransition(QQuickTransition *transition)
{
    Q_D(QQuickItemView);
    d->createTransitioner();
    if (d->transitioner->displacedTransition != transition) {
        d->transitioner->displacedTransition = transition;
        emit displacedTransitionChanged();
    }
}

void QQuickItemViewPrivate::positionViewAtIndex(int index, int mode)
{
    if (!isValid())
        return;
    if (mode < QQuickItemView::Beginning || mode > QQuickItemView::SnapPosition)
        return;

    Q_Q(QQuickItemView);
    q->cancelFlick();
    applyPendingChanges();
    const int modelCount = model->count();
    int idx = qMax(qMin(index, modelCount - 1), 0);

    const auto viewSize = size();
    qreal pos = isContentFlowReversed() ? -position() - viewSize : position();
    FxViewItem *item = visibleItem(idx);
    qreal maxExtent = calculatedMaxExtent();
    if (!item) {
        qreal itemPos = positionAt(idx);
        changedVisibleIndex(idx);
        // save the currently visible items in case any of them end up visible again
        const QList<FxViewItem *> oldVisible = visibleItems;
        visibleItems.clear();
        setPosition(qMin(itemPos, maxExtent));
        // now release the reference to all the old visible items.
        for (FxViewItem *item : oldVisible)
            releaseItem(item, reusableFlag);
        item = visibleItem(idx);
    }
    if (item) {
        const bool stickyHeader = hasStickyHeader();
        const bool stickyFooter = hasStickyFooter();
        const qreal stickyHeaderSize = stickyHeader ? headerSize() : 0;
        const qreal stickyFooterSize = stickyFooter ? footerSize() : 0;

        const qreal itemPos = item->position();
        switch (mode) {
        case QQuickItemView::Beginning:
            pos = itemPos;
            if (header && (index < 0 || stickyHeader))
                pos -= headerSize();
            break;
        case QQuickItemView::Center:
            pos = itemPos - (viewSize - item->size())/2;
            break;
        case QQuickItemView::End:
            pos = itemPos - viewSize + item->size();
            if (footer && (index >= modelCount || stickyFooter))
                pos += footerSize();
            break;
        case QQuickItemView::Visible:
            if (itemPos > pos + viewSize - stickyFooterSize)
                pos = item->endPosition() - viewSize + stickyFooterSize;
            else if (item->endPosition() <= pos - stickyHeaderSize)
                pos = itemPos - stickyHeaderSize;
            break;
        case QQuickItemView::Contain:
            if (item->endPosition() >= pos + viewSize + stickyFooterSize)
                pos = itemPos - viewSize + item->size() + stickyFooterSize;
            if (itemPos - stickyHeaderSize < pos)
                pos = itemPos - stickyHeaderSize;
            break;
        case QQuickItemView::SnapPosition:
            pos = itemPos - highlightRangeStart - stickyHeaderSize;
            break;
        }
        pos = qMin(pos, maxExtent);
        qreal minExtent = calculatedMinExtent();
        pos = qMax(pos, minExtent);
        moveReason = QQuickItemViewPrivate::Other;
        setPosition(pos);

        if (highlight) {
            if (autoHighlight)
                resetHighlightPosition();
            updateHighlight();
        }
    }
    fixupPosition();
}

void QQuickItemView::positionViewAtIndex(int index, int mode)
{
    Q_D(QQuickItemView);
    if (!d->isValid() || index < 0 || index >= d->model->count())
        return;
    d->positionViewAtIndex(index, mode);
}


void QQuickItemView::positionViewAtBeginning()
{
    Q_D(QQuickItemView);
    if (!d->isValid())
        return;
    d->positionViewAtIndex(-1, Beginning);
}

void QQuickItemView::positionViewAtEnd()
{
    Q_D(QQuickItemView);
    if (!d->isValid())
        return;
    d->positionViewAtIndex(d->model->count(), End);
}

static FxViewItem * fxViewItemAtPosition(const QList<FxViewItem *> &items, qreal x, qreal y)
{
    for (FxViewItem *item : items) {
        if (item->contains(x, y))
            return item;
    }
    return nullptr;
}

int QQuickItemView::indexAt(qreal x, qreal y) const
{
    Q_D(const QQuickItemView);
    const FxViewItem *item = fxViewItemAtPosition(d->visibleItems, x, y);
    return item ? item->index : -1;
}

QQuickItem *QQuickItemView::itemAt(qreal x, qreal y) const
{
    Q_D(const QQuickItemView);
    const FxViewItem *item = fxViewItemAtPosition(d->visibleItems, x, y);
    return item ? item->item : nullptr;
}

QQuickItem *QQuickItemView::itemAtIndex(int index) const
{
    Q_D(const QQuickItemView);
    const FxViewItem *item = d->visibleItem(index);
    return item ? item->item : nullptr;
}

void QQuickItemView::forceLayout()
{
    Q_D(QQuickItemView);
    if (isComponentComplete() && (d->currentChanges.hasPendingChanges() || d->forceLayout))
        d->layout();
}

void QQuickItemViewPrivate::applyPendingChanges()
{
    Q_Q(QQuickItemView);
    if (q->isComponentComplete() && currentChanges.hasPendingChanges())
        layout();
}

int QQuickItemViewPrivate::findMoveKeyIndex(QQmlChangeSet::MoveKey key, const QVector<QQmlChangeSet::Change> &changes) const
{
    for (int i=0; i<changes.count(); i++) {
        for (int j=changes[i].index; j<changes[i].index + changes[i].count; j++) {
            if (changes[i].moveKey(j) == key)
                return j;
        }
    }
    return -1;
}

qreal QQuickItemViewPrivate::minExtentForAxis(const AxisData &axisData, bool forXAxis) const
{
    Q_Q(const QQuickItemView);

    qreal highlightStart;
    qreal highlightEnd;
    qreal endPositionFirstItem = 0;
    qreal extent = -startPosition() + axisData.startMargin;
    if (isContentFlowReversed()) {
        if (model && model->count())
            endPositionFirstItem = positionAt(model->count()-1);
        else
            extent += headerSize();
        highlightStart = highlightRangeEndValid ? size() - highlightRangeEnd : size();
        highlightEnd = highlightRangeStartValid ? size() - highlightRangeStart : size();
        extent += footerSize();
        qreal maxExtentAlongAxis = forXAxis ? q->maxXExtent() : q->maxYExtent();
        if (extent < maxExtentAlongAxis)
            extent = maxExtentAlongAxis;
    } else {
        endPositionFirstItem = endPositionAt(0);
        highlightStart = highlightRangeStart;
        highlightEnd = highlightRangeEnd;
        extent += headerSize();
    }
    if (haveHighlightRange && highlightRange == QQuickItemView::StrictlyEnforceRange) {
        extent += highlightStart;
        FxViewItem *firstItem = visibleItem(0);
        if (firstItem)
            extent -= firstItem->sectionSize();
        extent = isContentFlowReversed()
                            ? qMin(extent, endPositionFirstItem + highlightEnd)
                            : qMax(extent, -(endPositionFirstItem - highlightEnd));
    }
    return extent;
}

qreal QQuickItemViewPrivate::maxExtentForAxis(const AxisData &axisData, bool forXAxis) const
{
    Q_Q(const QQuickItemView);

    qreal highlightStart;
    qreal highlightEnd;
    qreal lastItemPosition = 0;
    qreal extent = 0;
    if (isContentFlowReversed()) {
        highlightStart = highlightRangeEndValid ? size() - highlightRangeEnd : size();
        highlightEnd = highlightRangeStartValid ? size() - highlightRangeStart : size();
        lastItemPosition = endPosition();
    } else {
        highlightStart = highlightRangeStart;
        highlightEnd = highlightRangeEnd;
        if (model && model->count())
            lastItemPosition = positionAt(model->count()-1);
    }
    if (!model || !model->count()) {
        if (!isContentFlowReversed())
            maxExtent = header ? -headerSize() : 0;
        extent += forXAxis ? q->width() : q->height();
    } else if (haveHighlightRange && highlightRange == QQuickItemView::StrictlyEnforceRange) {
        extent = -(lastItemPosition - highlightStart);
        if (highlightEnd != highlightStart) {
            extent = isContentFlowReversed()
                    ? qMax(extent, -(endPosition() - highlightEnd))
                    : qMin(extent, -(endPosition() - highlightEnd));
        }
    } else {
        extent = -(endPosition() - (forXAxis ? q->width() : q->height()));
    }
    if (isContentFlowReversed()) {
        extent -= headerSize();
        extent -= axisData.endMargin;
    } else {
        extent -= footerSize();
        extent -= axisData.endMargin;
        qreal minExtentAlongAxis = forXAxis ? q->minXExtent() : q->minYExtent();
        if (extent > minExtentAlongAxis)
            extent = minExtentAlongAxis;
    }

    return extent;
}

qreal QQuickItemViewPrivate::calculatedMinExtent() const
{
    Q_Q(const QQuickItemView);
    qreal minExtent;
    if (layoutOrientation() == Qt::Vertical)
        minExtent = isContentFlowReversed() ? q->maxYExtent() - size(): -q->minYExtent();
    else
        minExtent = isContentFlowReversed() ? q->maxXExtent() - size(): -q->minXExtent();
    return minExtent;

}

qreal QQuickItemViewPrivate::calculatedMaxExtent() const
{
    Q_Q(const QQuickItemView);
    qreal maxExtent;
    if (layoutOrientation() == Qt::Vertical)
        maxExtent = isContentFlowReversed() ? q->minYExtent() - size(): -q->maxYExtent();
    else
        maxExtent = isContentFlowReversed() ? q->minXExtent() - size(): -q->maxXExtent();
    return maxExtent;
}

void QQuickItemViewPrivate::applyDelegateChange()
{
    releaseVisibleItems(QQmlDelegateModel::NotReusable);
    releaseItem(currentItem, QQmlDelegateModel::NotReusable);
    currentItem = nullptr;
    updateSectionCriteria();
    refill();
    moveReason = QQuickItemViewPrivate::SetIndex;
    updateCurrent(currentIndex);
    if (highlight && currentItem) {
        if (autoHighlight)
            resetHighlightPosition();
        updateTrackedItem();
    }
    moveReason = QQuickItemViewPrivate::Other;
    updateViewport();
}

// for debugging only
void QQuickItemViewPrivate::checkVisible() const
{
    int skip = 0;
    for (int i = 0; i < visibleItems.count(); ++i) {
        FxViewItem *item = visibleItems.at(i);
        if (item->index == -1) {
            ++skip;
        } else if (item->index != visibleIndex + i - skip) {
            qFatal("index %d %d %d", visibleIndex, i, item->index);
        }
    }
}

// for debugging only
void QQuickItemViewPrivate::showVisibleItems() const
{
    qDebug() << "Visible items:";
    for (FxViewItem *item : visibleItems) {
        qDebug() << "\t" << item->index
                 << item->item->objectName()
                 << item->position();
    }
}

void QQuickItemViewPrivate::itemGeometryChanged(QQuickItem *item, QQuickGeometryChange change,
                                                const QRectF &oldGeometry)
{
    Q_Q(QQuickItemView);
    QQuickFlickablePrivate::itemGeometryChanged(item, change, oldGeometry);
    if (!q->isComponentComplete())
        return;

    if (header && header->item == item) {
        updateHeader();
        markExtentsDirty();
        updateViewport();
        if (!q->isMoving() && !q->isFlicking())
            fixupPosition();
    } else if (footer && footer->item == item) {
        updateFooter();
        markExtentsDirty();
        updateViewport();
        if (!q->isMoving() && !q->isFlicking())
            fixupPosition();
    }

    if (currentItem && currentItem->item == item) {
        // don't allow item movement transitions to trigger a re-layout and
        // start new transitions
        bool prevInLayout = inLayout;
        if (!inLayout) {
            FxViewItem *actualItem = transitioner ? visibleItem(currentIndex) : nullptr;
            if (actualItem && actualItem->transitionRunning())
                inLayout = true;
        }
        updateHighlight();
        inLayout = prevInLayout;
    }

    if (trackedItem && trackedItem->item == item)
        q->trackedPositionChanged();
}

void QQuickItemView::destroyRemoved()
{
    Q_D(QQuickItemView);

    bool hasRemoveTransition = false;
    bool hasRemoveTransitionAsTarget = false;
    if (d->transitioner) {
        hasRemoveTransition = d->transitioner->canTransition(QQuickItemViewTransitioner::RemoveTransition, false);
        hasRemoveTransitionAsTarget = d->transitioner->canTransition(QQuickItemViewTransitioner::RemoveTransition, true);
    }

    for (QList<FxViewItem*>::Iterator it = d->visibleItems.begin();
            it != d->visibleItems.end();) {
        FxViewItem *item = *it;
        if (item->index == -1 && (!item->attached || item->attached->delayRemove() == false)) {
            if (hasRemoveTransitionAsTarget) {
                // don't remove from visibleItems until next layout()
                d->runDelayedRemoveTransition = true;
                QObject::disconnect(item->attached, SIGNAL(delayRemoveChanged()), this, SLOT(destroyRemoved()));
                ++it;
            } else {
                if (hasRemoveTransition)
                    d->runDelayedRemoveTransition = true;
                d->releaseItem(item, d->reusableFlag);
                it = d->visibleItems.erase(it);
            }
        } else {
            ++it;
        }
    }

    // Correct the positioning of the items
    d->forceLayoutPolish();
}

void QQuickItemView::modelUpdated(const QQmlChangeSet &changeSet, bool reset)
{
    Q_D(QQuickItemView);
    if (reset) {
        cancelFlick();
        if (d->transitioner)
            d->transitioner->setPopulateTransitionEnabled(true);
        d->moveReason = QQuickItemViewPrivate::SetIndex;
        d->regenerate();
        if (d->highlight && d->currentItem) {
            if (d->autoHighlight)
                d->resetHighlightPosition();
            d->updateTrackedItem();
        }
        d->moveReason = QQuickItemViewPrivate::Other;
        emit countChanged();
        if (d->transitioner && d->transitioner->populateTransition)
            d->forceLayoutPolish();
    } else {
        if (d->inLayout) {
            d->bufferedChanges.prepare(d->currentIndex, d->itemCount);
            d->bufferedChanges.applyChanges(changeSet);
        } else {
            if (d->bufferedChanges.hasPendingChanges()) {
                d->currentChanges.applyBufferedChanges(d->bufferedChanges);
                d->bufferedChanges.reset();
            }
            d->currentChanges.prepare(d->currentIndex, d->itemCount);
            d->currentChanges.applyChanges(changeSet);
        }
        polish();
    }
}

void QQuickItemView::animStopped()
{
    Q_D(QQuickItemView);
    d->bufferMode = QQuickItemViewPrivate::BufferBefore | QQuickItemViewPrivate::BufferAfter;
    d->refillOrLayout();
    if (d->haveHighlightRange && d->highlightRange == QQuickItemView::StrictlyEnforceRange)
        d->updateHighlight();
}


void QQuickItemView::trackedPositionChanged()
{
    Q_D(QQuickItemView);
    if (!d->trackedItem || !d->currentItem)
        return;

    if (d->inLayout) {
        polish();
        return;
    }

    if (d->moveReason == QQuickItemViewPrivate::SetIndex) {
        qreal trackedPos = d->trackedItem->position();
        qreal trackedSize = d->trackedItem->size();
        qreal viewPos = d->isContentFlowReversed() ? -d->position()-d->size() : d->position();
        qreal pos = viewPos;
        if (d->haveHighlightRange) {
            if (trackedPos > pos + d->highlightRangeEnd - trackedSize)
                pos = trackedPos - d->highlightRangeEnd + trackedSize;
            if (trackedPos < pos + d->highlightRangeStart)
                pos = trackedPos - d->highlightRangeStart;
            if (d->highlightRange != StrictlyEnforceRange) {
                qreal maxExtent = d->calculatedMaxExtent();
                if (pos > maxExtent)
                    pos = maxExtent;
                qreal minExtent = d->calculatedMinExtent();
                if (pos < minExtent)
                    pos = minExtent;
            }
        } else {
            if (d->trackedItem != d->currentItem) {
                // also make section header visible
                trackedPos -= d->currentItem->sectionSize();
                trackedSize += d->currentItem->sectionSize();
            }
            qreal trackedEndPos = d->trackedItem->endPosition();
            qreal toItemPos = d->currentItem->position();
            qreal toItemEndPos = d->currentItem->endPosition();
            if (d->showHeaderForIndex(d->currentIndex)) {
                qreal startOffset = -d->contentStartOffset();
                trackedPos -= startOffset;
                trackedEndPos -= startOffset;
                toItemPos -= startOffset;
                toItemEndPos -= startOffset;
            } else if (d->showFooterForIndex(d->currentIndex)) {
                qreal endOffset = d->footerSize();
                if (d->layoutOrientation() == Qt::Vertical) {
                    if (d->isContentFlowReversed())
                        endOffset += d->vData.startMargin;
                    else
                        endOffset += d->vData.endMargin;
                } else {
                    if (d->isContentFlowReversed())
                        endOffset += d->hData.startMargin;
                    else
                        endOffset += d->hData.endMargin;
                }
                trackedPos += endOffset;
                trackedEndPos += endOffset;
                toItemPos += endOffset;
                toItemEndPos += endOffset;
            }

            if (trackedEndPos >= viewPos + d->size()
                && toItemEndPos >= viewPos + d->size()) {
                if (trackedEndPos <= toItemEndPos) {
                    pos = trackedEndPos - d->size();
                    if (trackedSize > d->size())
                        pos = trackedPos;
                } else {
                    pos = toItemEndPos - d->size();
                    if (d->currentItem->size() > d->size())
                        pos = d->currentItem->position();
                }
            }
            if (trackedPos < pos && toItemPos < pos)
                pos = qMax(trackedPos, toItemPos);
        }
        if (viewPos != pos) {
            d->calcVelocity = true;
            d->setPosition(pos);
            d->calcVelocity = false;
        }
    }
}

void QQuickItemView::geometryChanged(const QRectF &newGeometry, const QRectF &oldGeometry)
{
    Q_D(QQuickItemView);
    d->markExtentsDirty();
    if (isComponentComplete() && (d->isValid() || !d->visibleItems.isEmpty()))
        d->forceLayoutPolish();
    QQuickFlickable::geometryChanged(newGeometry, oldGeometry);
}

qreal QQuickItemView::minYExtent() const
{
    Q_D(const QQuickItemView);
    if (d->layoutOrientation() == Qt::Horizontal)
        return QQuickFlickable::minYExtent();

    if (d->vData.minExtentDirty) {
        d->minExtent = d->minExtentForAxis(d->vData, false);
        d->vData.minExtentDirty = false;
    }

    return d->minExtent;
}

qreal QQuickItemView::maxYExtent() const
{
    Q_D(const QQuickItemView);
    if (d->layoutOrientation() == Qt::Horizontal)
        return height();

    if (d->vData.maxExtentDirty) {
        d->maxExtent = d->maxExtentForAxis(d->vData, false);
        d->vData.maxExtentDirty = false;
    }

    return d->maxExtent;
}

qreal QQuickItemView::minXExtent() const
{
    Q_D(const QQuickItemView);
    if (d->layoutOrientation() == Qt::Vertical)
        return QQuickFlickable::minXExtent();

    if (d->hData.minExtentDirty) {
        d->minExtent = d->minExtentForAxis(d->hData, true);
        d->hData.minExtentDirty = false;
    }

    return d->minExtent;
}

qreal QQuickItemView::maxXExtent() const
{
    Q_D(const QQuickItemView);
    if (d->layoutOrientation() == Qt::Vertical)
        return width();

    if (d->hData.maxExtentDirty) {
        d->maxExtent = d->maxExtentForAxis(d->hData, true);
        d->hData.maxExtentDirty = false;
    }

    return d->maxExtent;
}

void QQuickItemView::setContentX(qreal pos)
{
    Q_D(QQuickItemView);
    // Positioning the view manually should override any current movement state
    d->moveReason = QQuickItemViewPrivate::Other;
    QQuickFlickable::setContentX(pos);
}

void QQuickItemView::setContentY(qreal pos)
{
    Q_D(QQuickItemView);
    // Positioning the view manually should override any current movement state
    d->moveReason = QQuickItemViewPrivate::Other;
    QQuickFlickable::setContentY(pos);
}

qreal QQuickItemView::originX() const
{
    Q_D(const QQuickItemView);
    if (d->layoutOrientation() == Qt::Horizontal
            && effectiveLayoutDirection() == Qt::RightToLeft
            && contentWidth() < width()) {
        return -d->lastPosition() - d->footerSize();
    }
    return QQuickFlickable::originX();
}

qreal QQuickItemView::originY() const
{
    Q_D(const QQuickItemView);
    if (d->layoutOrientation() == Qt::Vertical
            && d->verticalLayoutDirection == QQuickItemView::BottomToTop
            && contentHeight() < height()) {
        return -d->lastPosition() - d->footerSize();
    }
    return QQuickFlickable::originY();
}

void QQuickItemView::updatePolish()
{
    Q_D(QQuickItemView);
    QQuickFlickable::updatePolish();
    d->layout();
}

void QQuickItemView::componentComplete()
{
    Q_D(QQuickItemView);
    if (d->model && d->ownModel)
        static_cast<QQmlDelegateModel *>(d->model.data())->componentComplete();

    QQuickFlickable::componentComplete();

    d->updateSectionCriteria();
    d->updateHeader();
    d->updateFooter();
    d->updateViewport();
    d->setPosition(d->contentStartOffset());
    if (d->transitioner)
        d->transitioner->setPopulateTransitionEnabled(true);

    if (d->isValid()) {
        d->refill();
        d->moveReason = QQuickItemViewPrivate::SetIndex;
        if (d->currentIndex < 0 && !d->currentIndexCleared)
            d->updateCurrent(0);
        else
            d->updateCurrent(d->currentIndex);
        if (d->highlight && d->currentItem) {
            if (d->autoHighlight)
                d->resetHighlightPosition();
            d->updateTrackedItem();
        }
        d->moveReason = QQuickItemViewPrivate::Other;
        d->fixupPosition();
    }
    if (d->model && d->model->count())
        emit countChanged();
}



QQuickItemViewPrivate::QQuickItemViewPrivate()
    : itemCount(0)
    , buffer(QML_VIEW_DEFAULTCACHEBUFFER), bufferMode(BufferBefore | BufferAfter)
    , displayMarginBeginning(0), displayMarginEnd(0)
    , layoutDirection(Qt::LeftToRight), verticalLayoutDirection(QQuickItemView::TopToBottom)
    , moveReason(Other)
    , visibleIndex(0)
    , currentIndex(-1), currentItem(nullptr)
    , trackedItem(nullptr), requestedIndex(-1)
    , highlightComponent(nullptr), highlight(nullptr)
    , highlightRange(QQuickItemView::NoHighlightRange)
    , highlightRangeStart(0), highlightRangeEnd(0)
    , highlightMoveDuration(150)
    , headerComponent(nullptr), header(nullptr), footerComponent(nullptr), footer(nullptr)
    , transitioner(nullptr)
    , minExtent(0), maxExtent(0)
    , ownModel(false), wrap(false)
    , keyNavigationEnabled(true)
    , explicitKeyNavigationEnabled(false)
    , inLayout(false), inViewportMoved(false), forceLayout(false), currentIndexCleared(false)
    , haveHighlightRange(false), autoHighlight(true), highlightRangeStartValid(false), highlightRangeEndValid(false)
    , fillCacheBuffer(false), inRequest(false)
    , runDelayedRemoveTransition(false), delegateValidated(false), isClearing(false)
{
    bufferPause.addAnimationChangeListener(this, QAbstractAnimationJob::Completion);
    bufferPause.setLoopCount(1);
    bufferPause.setDuration(16);
}

QQuickItemViewPrivate::~QQuickItemViewPrivate()
{
    if (transitioner)
        transitioner->setChangeListener(nullptr);
    delete transitioner;
}

bool QQuickItemViewPrivate::isValid() const
{
    return model && model->count() && model->isValid();
}

qreal QQuickItemViewPrivate::position() const
{
    Q_Q(const QQuickItemView);
    return layoutOrientation() == Qt::Vertical ? q->contentY() : q->contentX();
}

qreal QQuickItemViewPrivate::size() const
{
    Q_Q(const QQuickItemView);
    return layoutOrientation() == Qt::Vertical ? q->height() : q->width();
}

qreal QQuickItemViewPrivate::startPosition() const
{
    return isContentFlowReversed() ? -lastPosition() : originPosition();
}

qreal QQuickItemViewPrivate::endPosition() const
{
    return isContentFlowReversed() ? -originPosition() : lastPosition();
}

qreal QQuickItemViewPrivate::contentStartOffset() const
{
    qreal pos = -headerSize();
    if (layoutOrientation() == Qt::Vertical) {
        if (isContentFlowReversed())
            pos -= vData.endMargin;
        else
            pos -= vData.startMargin;
    } else {
        if (isContentFlowReversed())
            pos -= hData.endMargin;
        else
            pos -= hData.startMargin;
    }
    return pos;
}

int QQuickItemViewPrivate::findLastVisibleIndex(int defaultValue) const
{
    for (auto it = visibleItems.rbegin(), end = visibleItems.rend(); it != end; ++it) {
        auto item = *it;
        if (item->index != -1)
            return item->index;
    }
    return defaultValue;
}

FxViewItem *QQuickItemViewPrivate::visibleItem(int modelIndex) const {
    if (modelIndex >= visibleIndex && modelIndex < visibleIndex + visibleItems.count()) {
        for (int i = modelIndex - visibleIndex; i < visibleItems.count(); ++i) {
            FxViewItem *item = visibleItems.at(i);
            if (item->index == modelIndex)
                return item;
        }
    }
    return nullptr;
}

FxViewItem *QQuickItemViewPrivate::firstItemInView() const {
    const qreal pos = isContentFlowReversed() ? -position()-size() : position();
    for (FxViewItem *item : visibleItems) {
        if (item->index != -1 && item->endPosition() > pos)
            return item;
    }
    return visibleItems.count() ? visibleItems.first() : 0;
}

int QQuickItemViewPrivate::findLastIndexInView() const
{
    const qreal viewEndPos = isContentFlowReversed() ? -position() : position() + size();
    for (auto it = visibleItems.rbegin(), end = visibleItems.rend(); it != end; ++it) {
        auto item = *it;
        if (item->index != -1 && item->position() <= viewEndPos)
            return item->index;
    }
    return -1;
}

// Map a model index to visibleItems list index.
// These may differ if removed items are still present in the visible list,
// e.g. doing a removal animation
int QQuickItemViewPrivate::mapFromModel(int modelIndex) const
{
    if (modelIndex < visibleIndex || modelIndex >= visibleIndex + visibleItems.count())
        return -1;
    for (int i = 0; i < visibleItems.count(); ++i) {
        FxViewItem *item = visibleItems.at(i);
        if (item->index == modelIndex)
            return i;
        if (item->index > modelIndex)
            return -1;
    }
    return -1; // Not in visibleList
}

void QQuickItemViewPrivate::init()
{
    Q_Q(QQuickItemView);
    q->setFlag(QQuickItem::ItemIsFocusScope);
    QObject::connect(q, SIGNAL(movementEnded()), q, SLOT(animStopped()));
    QObject::connect(q, &QQuickFlickable::interactiveChanged, q, &QQuickItemView::keyNavigationEnabledChanged);
    q->setFlickableDirection(QQuickFlickable::VerticalFlick);
}

void QQuickItemViewPrivate::updateCurrent(int modelIndex)
{
    Q_Q(QQuickItemView);
    applyPendingChanges();
    if (!q->isComponentComplete() || !isValid() || modelIndex < 0 || modelIndex >= model->count()) {
        if (currentItem) {
            if (currentItem->attached)
                currentItem->attached->setIsCurrentItem(false);
            releaseItem(currentItem, reusableFlag);
            currentItem = nullptr;
            currentIndex = modelIndex;
            emit q->currentIndexChanged();
            emit q->currentItemChanged();
            updateHighlight();
        } else if (currentIndex != modelIndex) {
            currentIndex = modelIndex;
            emit q->currentIndexChanged();
        }
        return;
    }

    if (currentItem && currentIndex == modelIndex) {
        updateHighlight();
        return;
    }

    FxViewItem *oldCurrentItem = currentItem;
    int oldCurrentIndex = currentIndex;
    currentIndex = modelIndex;
    currentItem = createItem(modelIndex, QQmlIncubator::AsynchronousIfNested);
    if (oldCurrentItem && oldCurrentItem->attached && (!currentItem || oldCurrentItem->item != currentItem->item))
        oldCurrentItem->attached->setIsCurrentItem(false);
    if (currentItem) {
        currentItem->item->setFocus(true);
        if (currentItem->attached)
            currentItem->attached->setIsCurrentItem(true);
        initializeCurrentItem();
    }

    updateHighlight();
    if (oldCurrentIndex != currentIndex)
        emit q->currentIndexChanged();
    if (oldCurrentItem != currentItem
            && (!oldCurrentItem || !currentItem || oldCurrentItem->item != currentItem->item))
        emit q->currentItemChanged();
    releaseItem(oldCurrentItem, reusableFlag);
}

void QQuickItemViewPrivate::clear(bool onDestruction)
{
    Q_Q(QQuickItemView);

    isClearing = true;
    auto cleanup = qScopeGuard([this] { isClearing = false; });

    currentChanges.reset();
    bufferedChanges.reset();
    timeline.clear();

    releaseVisibleItems(QQmlInstanceModel::NotReusable);
    visibleIndex = 0;

    for (FxViewItem *item : qAsConst(releasePendingTransition)) {
        item->releaseAfterTransition = false;
        releaseItem(item, QQmlInstanceModel::NotReusable);
    }
    releasePendingTransition.clear();

    auto oldCurrentItem = currentItem;
    releaseItem(currentItem, QQmlDelegateModel::NotReusable);
    currentItem = nullptr;
    if (oldCurrentItem)
        emit q->currentItemChanged();
    createHighlight(onDestruction);
    trackedItem = nullptr;

    if (requestedIndex >= 0) {
        if (model)
            model->cancel(requestedIndex);
        requestedIndex = -1;
    }

    markExtentsDirty();
    itemCount = 0;
}


void QQuickItemViewPrivate::mirrorChange()
{
    Q_Q(QQuickItemView);
    regenerate();
    emit q->effectiveLayoutDirectionChanged();
}

void QQuickItemViewPrivate::animationFinished(QAbstractAnimationJob *)
{
    Q_Q(QQuickItemView);
    fillCacheBuffer = true;
    q->polish();
}

void QQuickItemViewPrivate::refill()
{
    qreal s = qMax(size(), qreal(0.));
    const auto pos = position();
    if (isContentFlowReversed())
        refill(-pos - displayMarginBeginning-s, -pos + displayMarginEnd);
    else
        refill(pos - displayMarginBeginning, pos + displayMarginEnd+s);
}

void QQuickItemViewPrivate::refill(qreal from, qreal to)
{
    Q_Q(QQuickItemView);
    if (!model || !model->isValid() || !q->isComponentComplete())
        return;
    if (!model->count()) {
        updateHeader();
        updateFooter();
        updateViewport();
        return;
    }

    do {
        bufferPause.stop();
        if (currentChanges.hasPendingChanges() || bufferedChanges.hasPendingChanges() || currentChanges.active) {
            currentChanges.reset();
            bufferedChanges.reset();
            releaseVisibleItems(reusableFlag);
        }

        int prevCount = itemCount;
        itemCount = model->count();
        qreal bufferFrom = from - buffer;
        qreal bufferTo = to + buffer;
        qreal fillFrom = from;
        qreal fillTo = to;

        bool added = addVisibleItems(fillFrom, fillTo, bufferFrom, bufferTo, false);
        bool removed = removeNonVisibleItems(bufferFrom, bufferTo);

        if (requestedIndex == -1 && buffer && bufferMode != NoBuffer) {
            if (added) {
                // We've already created a new delegate this frame.
                // Just schedule a buffer refill.
                bufferPause.start();
            } else {
                if (bufferMode & BufferAfter)
                    fillTo = bufferTo;
                if (bufferMode & BufferBefore)
                    fillFrom = bufferFrom;
                added |= addVisibleItems(fillFrom, fillTo, bufferFrom, bufferTo, true);
            }
        }

        if (added || removed) {
            markExtentsDirty();
            updateBeginningEnd();
            visibleItemsChanged();
            updateHeader();
            updateFooter();
            updateViewport();
        }

        if (prevCount != itemCount)
            emit q->countChanged();
    } while (currentChanges.hasPendingChanges() || bufferedChanges.hasPendingChanges());
    storeFirstVisibleItemPosition();
}

void QQuickItemViewPrivate::regenerate(bool orientationChanged)
{
    Q_Q(QQuickItemView);
    if (q->isComponentComplete()) {
        if (orientationChanged) {
            delete header;
            header = nullptr;
            delete footer;
            footer = nullptr;
        }
        clear();
        updateHeader();
        updateFooter();
        updateViewport();
        setPosition(contentStartOffset());
        refill();
        updateCurrent(currentIndex);
    }
}

void QQuickItemViewPrivate::updateViewport()
{
    Q_Q(QQuickItemView);
    qreal extra = headerSize() + footerSize();
    qreal contentSize = isValid() || !visibleItems.isEmpty() ? (endPosition() - startPosition()) : 0.0;
    if (layoutOrientation() == Qt::Vertical)
        q->setContentHeight(contentSize + extra);
    else
        q->setContentWidth(contentSize + extra);
}

void QQuickItemViewPrivate::layout()
{
    Q_Q(QQuickItemView);
    if (inLayout)
        return;

    inLayout = true;

    // viewBounds contains bounds before any add/remove/move operation to the view
    QRectF viewBounds(q->contentX(),  q->contentY(), q->width(), q->height());

    if (!isValid() && !visibleItems.count()) {
        clear();
        setPosition(contentStartOffset());
        updateViewport();
        if (transitioner)
            transitioner->setPopulateTransitionEnabled(false);
        inLayout = false;
        return;
    }

    if (runDelayedRemoveTransition && transitioner
            && transitioner->canTransition(QQuickItemViewTransitioner::RemoveTransition, false)) {
        // assume that any items moving now are moving due to the remove - if they schedule
        // a different transition, that will override this one anyway
        for (int i=0; i<visibleItems.count(); i++)
            visibleItems[i]->transitionNextReposition(transitioner, QQuickItemViewTransitioner::RemoveTransition, false);
    }

    ChangeResult insertionPosChanges;
    ChangeResult removalPosChanges;
    if (!applyModelChanges(&insertionPosChanges, &removalPosChanges) && !forceLayout) {
        if (fillCacheBuffer) {
            fillCacheBuffer = false;
            refill();
        }
        inLayout = false;
        return;
    }
    forceLayout = false;

    if (transitioner && transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true)) {
        // Give the view one more chance to refill itself,
        // in case its size is changed such that more delegates become visible after component completed
        refill();
        for (FxViewItem *item : qAsConst(visibleItems)) {
            if (!item->transitionScheduledOrRunning())
                item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::PopulateTransition, true);
        }
    }

    updateSections();
    layoutVisibleItems();
    storeFirstVisibleItemPosition();

    int lastIndexInView = findLastIndexInView();
    refill();
    markExtentsDirty();
    updateHighlight();

    if (!q->isMoving() && !q->isFlicking() && !movingFromHighlight()) {
        fixupPosition();
        refill();
    }

    updateHeader();
    updateFooter();
    updateViewport();
    updateUnrequestedPositions();

    if (transitioner) {
        // items added in the last refill() may need to be transitioned in - e.g. a remove
        // causes items to slide up into view
        if (lastIndexInView != -1 &&
            (transitioner->canTransition(QQuickItemViewTransitioner::MoveTransition, false)
                || transitioner->canTransition(QQuickItemViewTransitioner::RemoveTransition, false))) {
            translateAndTransitionItemsAfter(lastIndexInView, insertionPosChanges, removalPosChanges);
        }

        prepareVisibleItemTransitions();

        // We cannot use iterators here as erasing from a container invalidates them.
        for (int i = 0, count = releasePendingTransition.count(); i < count;) {
            auto success = prepareNonVisibleItemTransition(releasePendingTransition[i], viewBounds);
            // prepareNonVisibleItemTransition() may remove items while in fast flicking.
            // Invisible animating items are kicked in or out the viewPort.
            // Recheck count to test if the item got removed. In that case the same index points
            // to a different item now.
            const int old_count = count;
            count = releasePendingTransition.count();
            if (old_count > count)
                continue;

            if (!success) {
                releaseItem(releasePendingTransition[i], reusableFlag);
                releasePendingTransition.remove(i);
                --count;
            } else {
                ++i;
            }
        }

        for (int i=0; i<visibleItems.count(); i++)
            visibleItems[i]->startTransition(transitioner);
        for (int i=0; i<releasePendingTransition.count(); i++)
            releasePendingTransition[i]->startTransition(transitioner);

        transitioner->setPopulateTransitionEnabled(false);
        transitioner->resetTargetLists();
    }

    runDelayedRemoveTransition = false;
    inLayout = false;
}

bool QQuickItemViewPrivate::applyModelChanges(ChangeResult *totalInsertionResult, ChangeResult *totalRemovalResult)
{
    Q_Q(QQuickItemView);
    if (!q->isComponentComplete() || !hasPendingChanges())
        return false;

    if (bufferedChanges.hasPendingChanges()) {
        currentChanges.applyBufferedChanges(bufferedChanges);
        bufferedChanges.reset();
    }

    updateUnrequestedIndexes();

    FxViewItem *prevVisibleItemsFirst = visibleItems.count() ? *visibleItems.constBegin() : 0;
    int prevItemCount = itemCount;
    int prevVisibleItemsCount = visibleItems.count();
    bool visibleAffected = false;
    bool viewportChanged = !currentChanges.pendingChanges.removes().isEmpty()
            || !currentChanges.pendingChanges.inserts().isEmpty();

    FxViewItem *prevFirstItemInView = firstItemInView();
    QQmlNullableValue<qreal> prevFirstItemInViewPos;
    int prevFirstItemInViewIndex = -1;
    if (prevFirstItemInView) {
        prevFirstItemInViewPos = prevFirstItemInView->position();
        prevFirstItemInViewIndex = prevFirstItemInView->index;
    }
    qreal prevVisibleItemsFirstPos = visibleItems.count() ? firstVisibleItemPosition : 0.0;

    totalInsertionResult->visiblePos = prevFirstItemInViewPos;
    totalRemovalResult->visiblePos = prevFirstItemInViewPos;

    const QVector<QQmlChangeSet::Change> &removals = currentChanges.pendingChanges.removes();
    const QVector<QQmlChangeSet::Change> &insertions = currentChanges.pendingChanges.inserts();
    ChangeResult insertionResult(prevFirstItemInViewPos);
    ChangeResult removalResult(prevFirstItemInViewPos);

    int removedCount = 0;
    for (const QQmlChangeSet::Change &r : removals) {
        itemCount -= r.count;
        if (applyRemovalChange(r, &removalResult, &removedCount))
            visibleAffected = true;
        if (!visibleAffected && needsRefillForAddedOrRemovedIndex(r.index))
            visibleAffected = true;
        const int correctedFirstVisibleIndex = prevFirstItemInViewIndex - removalResult.countChangeBeforeVisible;
        if (correctedFirstVisibleIndex >= 0 && r.index < correctedFirstVisibleIndex) {
            if (r.index + r.count < correctedFirstVisibleIndex)
                removalResult.countChangeBeforeVisible += r.count;
            else
                removalResult.countChangeBeforeVisible += (correctedFirstVisibleIndex  - r.index);
        }
    }
    if (runDelayedRemoveTransition) {
        QQmlChangeSet::Change removal;
        for (QList<FxViewItem*>::Iterator it = visibleItems.begin(); it != visibleItems.end();) {
            FxViewItem *item = *it;
            if (item->index == -1 && (!item->attached || !item->attached->delayRemove())) {
                removeItem(item, removal, &removalResult);
                removedCount++;
                it = visibleItems.erase(it);
            } else {
               ++it;
            }
        }
    }
    *totalRemovalResult += removalResult;
    if (!removals.isEmpty()) {
        updateVisibleIndex();

        // set positions correctly for the next insertion
        if (!insertions.isEmpty()) {
            repositionFirstItem(prevVisibleItemsFirst, prevVisibleItemsFirstPos, prevFirstItemInView, &insertionResult, &removalResult);
            layoutVisibleItems(removals.first().index);
            storeFirstVisibleItemPosition();
        }
    }

    QList<FxViewItem *> newItems;
    QList<MovedItem> movingIntoView;

    for (int i=0; i<insertions.count(); i++) {
        bool wasEmpty = visibleItems.isEmpty();
        if (applyInsertionChange(insertions[i], &insertionResult, &newItems, &movingIntoView))
            visibleAffected = true;
        if (!visibleAffected && needsRefillForAddedOrRemovedIndex(insertions[i].index))
            visibleAffected = true;
        if (wasEmpty && !visibleItems.isEmpty())
            resetFirstItemPosition();
        *totalInsertionResult += insertionResult;

        // set positions correctly for the next insertion
        if (i < insertions.count() - 1) {
            repositionFirstItem(prevVisibleItemsFirst, prevVisibleItemsFirstPos, prevFirstItemInView, &insertionResult, &removalResult);
            layoutVisibleItems(insertions[i].index);
            storeFirstVisibleItemPosition();
        }
        itemCount += insertions[i].count;
    }
    for (FxViewItem *item : qAsConst(newItems)) {
        if (item->attached)
            item->attached->emitAdd();
    }

    // for each item that was moved directly into the view as a result of a move(),
    // find the index it was moved from in order to set its initial position, so that we
    // can transition it from this "original" position to its new position in the view
    if (transitioner && transitioner->canTransition(QQuickItemViewTransitioner::MoveTransition, true)) {
        for (const MovedItem &m : qAsConst(movingIntoView)) {
            int fromIndex = findMoveKeyIndex(m.moveKey, removals);
            if (fromIndex >= 0) {
                if (prevFirstItemInViewIndex >= 0 && fromIndex < prevFirstItemInViewIndex)
                    repositionItemAt(m.item, fromIndex, -totalInsertionResult->sizeChangesAfterVisiblePos);
                else
                    repositionItemAt(m.item, fromIndex, totalInsertionResult->sizeChangesAfterVisiblePos);
                m.item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::MoveTransition, true);
            }
        }
    }

    // reposition visibleItems.first() correctly so that the content y doesn't jump
    if (removedCount != prevVisibleItemsCount)
        repositionFirstItem(prevVisibleItemsFirst, prevVisibleItemsFirstPos, prevFirstItemInView, &insertionResult, &removalResult);

    // Whatever removed/moved items remain are no longer visible items.
    prepareRemoveTransitions(&currentChanges.removedItems);
    for (auto it = currentChanges.removedItems.begin();
         it != currentChanges.removedItems.end(); ++it) {
        releaseItem(it.value(), reusableFlag);
    }
    currentChanges.removedItems.clear();

    if (currentChanges.currentChanged) {
        if (currentChanges.currentRemoved && currentItem) {
            if (currentItem->item && currentItem->attached)
                currentItem->attached->setIsCurrentItem(false);
            auto oldCurrentItem = currentItem;
            releaseItem(currentItem, reusableFlag);
            currentItem = nullptr;
            if (oldCurrentItem)
                emit q->currentItemChanged();
        }
        if (!currentIndexCleared)
            updateCurrent(currentChanges.newCurrentIndex);
    }

    if (!visibleAffected)
        visibleAffected = !currentChanges.pendingChanges.changes().isEmpty();
    currentChanges.reset();

    updateSections();
    if (prevItemCount != itemCount)
        emit q->countChanged();
    if (!visibleAffected && viewportChanged)
        updateViewport();

    return visibleAffected;
}

bool QQuickItemViewPrivate::applyRemovalChange(const QQmlChangeSet::Change &removal, ChangeResult *removeResult, int *removedCount)
{
    Q_Q(QQuickItemView);
    bool visibleAffected = false;

    if (visibleItems.count() && removal.index + removal.count > visibleItems.constLast()->index) {
        if (removal.index > visibleItems.constLast()->index)
            removeResult->countChangeAfterVisibleItems += removal.count;
        else
            removeResult->countChangeAfterVisibleItems += ((removal.index + removal.count - 1) - visibleItems.constLast()->index);
    }

    QList<FxViewItem*>::Iterator it = visibleItems.begin();
    while (it != visibleItems.end()) {
        FxViewItem *item = *it;
        if (item->index == -1 || item->index < removal.index) {
            // already removed, or before removed items
            if (!visibleAffected && item->index < removal.index)
                visibleAffected = true;
            ++it;
        } else if (item->index >= removal.index + removal.count) {
            // after removed items
            item->index -= removal.count;
            if (removal.isMove())
                item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::MoveTransition, false);
            else
                item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::RemoveTransition, false);
            ++it;
        } else {
            // removed item
            visibleAffected = true;
            if (!removal.isMove() && item->item && item->attached)
                item->attached->emitRemove();

            if (item->item && item->attached && item->attached->delayRemove() && !removal.isMove()) {
                item->index = -1;
                QObject::connect(item->attached, SIGNAL(delayRemoveChanged()), q, SLOT(destroyRemoved()), Qt::QueuedConnection);
                ++it;
            } else {
                removeItem(item, removal, removeResult);
                if (!removal.isMove())
                    (*removedCount)++;
                it = visibleItems.erase(it);
            }
        }
    }

    return visibleAffected;
}

void QQuickItemViewPrivate::removeItem(FxViewItem *item, const QQmlChangeSet::Change &removal, ChangeResult *removeResult)
{
    if (removeResult->visiblePos.isValid()) {
        if (item->position() < removeResult->visiblePos)
            updateSizeChangesBeforeVisiblePos(item, removeResult);
        else
            removeResult->sizeChangesAfterVisiblePos += item->size();
    }
    if (removal.isMove()) {
        currentChanges.removedItems.replace(removal.moveKey(item->index), item);
        item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::MoveTransition, true);
    } else {
        // track item so it is released later
        currentChanges.removedItems.insert(QQmlChangeSet::MoveKey(), item);
    }
    if (!removeResult->changedFirstItem && item == *visibleItems.constBegin())
        removeResult->changedFirstItem = true;
}

void QQuickItemViewPrivate::updateSizeChangesBeforeVisiblePos(FxViewItem *item, ChangeResult *removeResult)
{
    removeResult->sizeChangesBeforeVisiblePos += item->size();
}

void QQuickItemViewPrivate::repositionFirstItem(FxViewItem *prevVisibleItemsFirst,
                                                   qreal prevVisibleItemsFirstPos,
                                                   FxViewItem *prevFirstVisible,
                                                   ChangeResult *insertionResult,
                                                   ChangeResult *removalResult)
{
    const QQmlNullableValue<qreal> prevViewPos = insertionResult->visiblePos;

    // reposition visibleItems.first() correctly so that the content y doesn't jump
    if (visibleItems.count()) {
        if (prevVisibleItemsFirst && insertionResult->changedFirstItem)
            resetFirstItemPosition(prevVisibleItemsFirstPos);

        if (prevFirstVisible && prevVisibleItemsFirst == prevFirstVisible
                && prevFirstVisible != *visibleItems.constBegin()) {
            // the previous visibleItems.first() was also the first visible item, and it has been
            // moved/removed, so move the new visibleItems.first() to the pos of the previous one
            if (!insertionResult->changedFirstItem)
                resetFirstItemPosition(prevVisibleItemsFirstPos);

        } else if (prevViewPos.isValid()) {
            qreal moveForwardsBy = 0;
            qreal moveBackwardsBy = 0;

            // shift visibleItems.first() relative to the number of added/removed items
            const auto pos = visibleItems.constFirst()->position();
            if (pos > prevViewPos) {
                moveForwardsBy = insertionResult->sizeChangesAfterVisiblePos;
                moveBackwardsBy = removalResult->sizeChangesAfterVisiblePos;
            } else if (pos < prevViewPos) {
                moveForwardsBy = removalResult->sizeChangesBeforeVisiblePos;
                moveBackwardsBy = insertionResult->sizeChangesBeforeVisiblePos;
            }
            adjustFirstItem(moveForwardsBy, moveBackwardsBy, insertionResult->countChangeBeforeVisible - removalResult->countChangeBeforeVisible);
        }
        insertionResult->reset();
        removalResult->reset();
    }
}

void QQuickItemViewPrivate::createTransitioner()
{
    if (!transitioner) {
        transitioner = new QQuickItemViewTransitioner;
        transitioner->setChangeListener(this);
    }
}

void QQuickItemViewPrivate::prepareVisibleItemTransitions()
{
    Q_Q(QQuickItemView);
    if (!transitioner)
        return;

    // must call for every visible item to init or discard transitions
    QRectF viewBounds(q->contentX(), q->contentY(), q->width(), q->height());
    for (int i=0; i<visibleItems.count(); i++)
        visibleItems[i]->prepareTransition(transitioner, viewBounds);
}

void QQuickItemViewPrivate::prepareRemoveTransitions(QMultiHash<QQmlChangeSet::MoveKey, FxViewItem *> *removedItems)
{
    if (!transitioner)
        return;

    if (transitioner->canTransition(QQuickItemViewTransitioner::RemoveTransition, true)
            || transitioner->canTransition(QQuickItemViewTransitioner::RemoveTransition, false)) {
        for (auto it = removedItems->begin(); it != removedItems->end(); ) {
            bool isRemove = it.key().moveId < 0;
            if (isRemove) {
                FxViewItem *item = *it;
                item->trackGeometry(false);
                item->releaseAfterTransition = true;
                releasePendingTransition.append(item);
                item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::RemoveTransition, true);
                it = removedItems->erase(it);
            } else {
                ++it;
            }
        }
    }
}

bool QQuickItemViewPrivate::prepareNonVisibleItemTransition(FxViewItem *item, const QRectF &viewBounds)
{
    // Called for items that have been removed from visibleItems and may now be
    // transitioned out of the view. This applies to items that are being directly
    // removed, or moved to outside of the view, as well as those that are
    // displaced to a position outside of the view due to an insert or move.

    if (!transitioner)
        return false;

    if (item->scheduledTransitionType() == QQuickItemViewTransitioner::MoveTransition)
        repositionItemAt(item, item->index, 0);

    bool success = false;
    ACTION_IF_DELETED(item, success = item->prepareTransition(transitioner, viewBounds), return success);

    if (success) {
        item->releaseAfterTransition = true;
        return true;
    }
    return false;
}

void QQuickItemViewPrivate::viewItemTransitionFinished(QQuickItemViewTransitionableItem *item)
{
    for (int i=0; i<releasePendingTransition.count(); i++) {
        if (releasePendingTransition.at(i)->transitionableItem == item) {
            releaseItem(releasePendingTransition.takeAt(i), reusableFlag);
            return;
        }
    }
}

/*
  This may return 0 if the item is being created asynchronously.
  When the item becomes available, refill() will be called and the item
  will be returned on the next call to createItem().
*/
FxViewItem *QQuickItemViewPrivate::createItem(int modelIndex, QQmlIncubator::IncubationMode incubationMode)
{
    Q_Q(QQuickItemView);

    if (requestedIndex == modelIndex && incubationMode == QQmlIncubator::Asynchronous)
        return nullptr;

    for (int i=0; i<releasePendingTransition.count(); i++) {
        if (releasePendingTransition.at(i)->index == modelIndex
                && !releasePendingTransition.at(i)->isPendingRemoval()) {
            releasePendingTransition[i]->releaseAfterTransition = false;
            return releasePendingTransition.takeAt(i);
        }
    }

    inRequest = true;

    // The model will run this same range check internally but produce a warning and return nullptr.
    // Since we handle this result graciously in our code, we preempt this warning by checking the range ourselves.
    QObject* object = modelIndex < model->count() ? model->object(modelIndex, incubationMode) : nullptr;
    QQuickItem *item = qmlobject_cast<QQuickItem*>(object);

    if (!item) {
        if (!object) {
            if (requestedIndex == -1 && model->incubationStatus(modelIndex) == QQmlIncubator::Loading) {
                // The reason we didn't receive an item is because it's incubating async. We keep track
                // of this by assigning the index we're waiting for to 'requestedIndex'. This will e.g. let
                // the view avoid unnecessary layout calls until the item has been loaded.
                requestedIndex = modelIndex;
            }
        } else {
            model->release(object);
            if (!delegateValidated) {
                delegateValidated = true;
                QObject* delegate = q->delegate();
                qmlWarning(delegate ? delegate : q) << QQuickItemView::tr("Delegate must be of Item type");
            }
        }
        inRequest = false;
        return nullptr;
    } else {
        item->setParentItem(q->contentItem());
        if (requestedIndex == modelIndex)
            requestedIndex = -1;
        FxViewItem *viewItem = newViewItem(modelIndex, item);
        if (viewItem) {
            viewItem->index = modelIndex;
            // do other set up for the new item that should not happen
            // until after bindings are evaluated
            initializeViewItem(viewItem);
            unrequestedItems.remove(item);
        }
        inRequest = false;
        return viewItem;
    }
}

void QQuickItemView::createdItem(int index, QObject* object)
{
    Q_D(QQuickItemView);

    QQuickItem* item = qmlobject_cast<QQuickItem*>(object);
    if (!d->inRequest) {
        d->unrequestedItems.insert(item, index);
        d->requestedIndex = -1;
        if (d->hasPendingChanges())
            d->layout();
        else
            d->refill();
        if (d->unrequestedItems.contains(item))
            d->repositionPackageItemAt(item, index);
        else if (index == d->currentIndex)
            d->updateCurrent(index);
    }
}

void QQuickItemView::initItem(int, QObject *object)
{
    QQuickItem* item = qmlobject_cast<QQuickItem*>(object);
    if (item) {
        if (qFuzzyIsNull(item->z()))
            item->setZ(1);
        item->setParentItem(contentItem());
        QQuickItemPrivate::get(item)->setCulled(true);
    }
}

void QQuickItemView::destroyingItem(QObject *object)
{
    Q_D(QQuickItemView);
    QQuickItem* item = qmlobject_cast<QQuickItem*>(object);
    if (item) {
        item->setParentItem(nullptr);
        d->unrequestedItems.remove(item);
    }
}

void QQuickItemView::onItemPooled(int modelIndex, QObject *object)
{
    Q_UNUSED(modelIndex);

    if (auto *attached = d_func()->getAttachedObject(object))
        emit attached->pooled();
}

void QQuickItemView::onItemReused(int modelIndex, QObject *object)
{
    Q_UNUSED(modelIndex);

    if (auto *attached = d_func()->getAttachedObject(object))
        emit attached->reused();
}

bool QQuickItemViewPrivate::releaseItem(FxViewItem *item, QQmlInstanceModel::ReusableFlag reusableFlag)
{
    Q_Q(QQuickItemView);
    if (!item)
        return true;
    if (trackedItem == item)
        trackedItem = nullptr;
    item->trackGeometry(false);

    QQmlInstanceModel::ReleaseFlags flags = {};
    if (model && item->item) {
        flags = model->release(item->item, reusableFlag);
        if (!flags) {
            // item was not destroyed, and we no longer reference it.
            if (item->item->parentItem() == contentItem) {
                // Only cull the item if its parent item is still our contentItem.
                // One case where this can happen is moving an item out of one ObjectModel and into another.
                QQuickItemPrivate::get(item->item)->setCulled(true);
            }
            if (!isClearing)
                unrequestedItems.insert(item->item, model->indexOf(item->item, q));
        } else if (flags & QQmlInstanceModel::Destroyed) {
            item->item->setParentItem(nullptr);
        } else if (flags & QQmlInstanceModel::Pooled) {
            item->setVisible(false);
        }
    }
    delete item;
    return flags != QQmlInstanceModel::Referenced;
}

QQuickItem *QQuickItemViewPrivate::createHighlightItem() const
{
    return createComponentItem(highlightComponent, 0.0, true);
}

QQuickItem *QQuickItemViewPrivate::createComponentItem(QQmlComponent *component, qreal zValue, bool createDefault) const
{
    Q_Q(const QQuickItemView);

    QQuickItem *item = nullptr;
    if (component) {
        QQmlContext *creationContext = component->creationContext();
        QQmlContext *context = new QQmlContext(
                creationContext ? creationContext : qmlContext(q));
        QObject *nobj = component->beginCreate(context);
        if (nobj) {
            QQml_setParent_noEvent(context, nobj);
            item = qobject_cast<QQuickItem *>(nobj);
            if (!item)
                delete nobj;
        } else {
            delete context;
        }
    } else if (createDefault) {
        item = new QQuickItem;
    }
    if (item) {
        if (qFuzzyIsNull(item->z()))
            item->setZ(zValue);
        QQml_setParent_noEvent(item, q->contentItem());
        item->setParentItem(q->contentItem());
    }
    if (component)
        component->completeCreate();
    return item;
}

void QQuickItemViewPrivate::updateTrackedItem()
{
    Q_Q(QQuickItemView);
    FxViewItem *item = currentItem;
    if (highlight)
        item = highlight;
    trackedItem = item;

    if (trackedItem)
        q->trackedPositionChanged();
}

void QQuickItemViewPrivate::updateUnrequestedIndexes()
{
    Q_Q(QQuickItemView);
    for (QHash<QQuickItem*,int>::iterator it = unrequestedItems.begin(), end = unrequestedItems.end(); it != end; ++it)
        *it = model->indexOf(it.key(), q);
}

void QQuickItemViewPrivate::updateUnrequestedPositions()
{
    for (QHash<QQuickItem*,int>::const_iterator it = unrequestedItems.cbegin(), cend = unrequestedItems.cend(); it != cend; ++it) {
        if (it.value() >= 0)
            repositionPackageItemAt(it.key(), it.value());
    }
}

void QQuickItemViewPrivate::updateVisibleIndex()
{
    typedef QList<FxViewItem*>::const_iterator FxViewItemListConstIt;

    visibleIndex = 0;
    for (FxViewItemListConstIt it = visibleItems.constBegin(), cend = visibleItems.constEnd(); it != cend; ++it) {
        if ((*it)->index != -1) {
            visibleIndex = (*it)->index;
            break;
        }
    }
}

QT_END_NAMESPACE

#include "moc_qquickitemview_p.cpp"
