Add itemAtIndex to quick views

This patch adds itemAtIndex method to ItemView-derived views and
to PathView.

[ChangeLog][QtQuick][QQuickItemView] Added itemAtIndex() to
GridView, ListView and PathView to fetch a visible delegate by index.

Change-Id: Id8475d06c1481036984fe5109bb52cf2729b1c21
Fixes: QTBUG-72961
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/quick/items/qquickgridview.cpp

@@ -2636,6 +2636,19 @@ bool QQuickGridViewPrivate::needsRefillForAddedOrRemovedIndex(int modelIndex) co
     \b Note: methods should only be called after the Component has completed.
 */
 
+/*!
+    \qmlmethod Item QtQuick::GridView::itemAtIndex(int index)
+
+    Returns the item for \a index. If there is no item for that index, for example
+    because it has not been created yet, or because it has been panned out of
+    the visible area and removed from the cache, null is returned.
+
+    \b Note: this method should only be called after the Component has completed.
+    The returned value should also not be stored since it can turn to null
+    as soon as control goes out of the calling scope, if the view releases that item.
+
+    \since 5.13
+*/
 
 /*!
     \qmlmethod QtQuick::GridView::forceLayout()

src/quick/items/qquickitemsmodule.cpp

@@ -472,6 +472,10 @@ static void qt_quickitems_defineModule(const char *uri, int major, int minor)
 #if QT_CONFIG(quick_tableview)
     qmlRegisterType<QQuickTableView>(uri, 2, 12, "TableView");
 #endif
+
+    qmlRegisterUncreatableType<QQuickItemView, 13>(uri, 2, 13, itemViewName, itemViewMessage);
+    qmlRegisterType<QQuickPathView, 13>(uri, 2, 13, "PathView");
+    qmlRegisterType<QQuickGridView, 13>(uri, 2, 13, "GridView");
 }
 
 static void initResources()

src/quick/items/qquickitemview.cpp

@@ -951,6 +951,13 @@ QQuickItem *QQuickItemView::itemAt(qreal x, qreal y) const
     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);

src/quick/items/qquickitemview_p.h

@@ -228,6 +228,7 @@ public:
     Q_INVOKABLE void positionViewAtIndex(int index, int mode);
     Q_INVOKABLE int indexAt(qreal x, qreal y) const;
     Q_INVOKABLE QQuickItem *itemAt(qreal x, qreal y) const;
+    Q_REVISION(13) Q_INVOKABLE QQuickItem *itemAtIndex(int index) const;
     Q_INVOKABLE void positionViewAtBeginning();
     Q_INVOKABLE void positionViewAtEnd();
     Q_REVISION(1) Q_INVOKABLE void forceLayout();

src/quick/items/qquicklistview.cpp

@@ -3512,6 +3512,20 @@ void QQuickListViewPrivate::translateAndTransitionItemsAfter(int afterModelIndex
     \b Note: methods should only be called after the Component has completed.
 */
 
+/*!
+    \qmlmethod Item QtQuick::ListView::itemAtIndex(int index)
+
+    Returns the item for \a index. If there is no item for that index, for example
+    because it has not been created yet, or because it has been panned out of
+    the visible area and removed from the cache, null is returned.
+
+    \b Note: this method should only be called after the Component has completed.
+    The returned value should also not be stored since it can turn to null
+    as soon as control goes out of the calling scope, if the view releases that item.
+
+    \since 5.13
+*/
+
 /*!
     \qmlmethod QtQuick::ListView::forceLayout()
 

src/quick/items/qquickpathview.cpp

@@ -1550,6 +1550,33 @@ QQuickItem *QQuickPathView::itemAt(qreal x, qreal y) const
     return nullptr;
 }
 
+/*!
+    \qmlmethod Item QtQuick::QQuickPathView::itemAtIndex(int index)
+
+    Returns the item for \a index. If there is no item for that index, for example
+    because it has not been created yet, or because it has been panned out of
+    the visible area and removed from the cache, null is returned.
+
+    \b Note: this method should only be called after the Component has completed.
+    The returned value should also not be stored since it can turn to null
+    as soon as control goes out of the calling scope, if the view releases that item.
+
+    \since 5.13
+*/
+QQuickItem *QQuickPathView::itemAtIndex(int index) const
+{
+    Q_D(const QQuickPathView);
+    if (!d->isValid())
+        return nullptr;
+
+    for (QQuickItem *item : d->items) {
+        if (index ==  d->model->indexOf(item, nullptr))
+            return item;
+    }
+
+    return nullptr;
+}
+
 QPointF QQuickPathViewPrivate::pointNear(const QPointF &point, qreal *nearPercent) const
 {
     const auto pathLength = path->path().length();

src/quick/items/qquickpathview_p.h

@@ -180,6 +180,7 @@ public:
     Q_INVOKABLE void positionViewAtIndex(int index, int mode);
     Q_INVOKABLE int indexAt(qreal x, qreal y) const;
     Q_INVOKABLE QQuickItem *itemAt(qreal x, qreal y) const;
+    Q_REVISION(13) Q_INVOKABLE QQuickItem *itemAtIndex(int index) const;
 
     static QQuickPathViewAttached *qmlAttachedProperties(QObject *);
 

tests/auto/quick/qquicklistview/data/listview-itematindex.qml

@@ -0,0 +1,15 @@
+import QtQuick 2.0
+
+ListView {
+    width: 400
+    height: 400
+    focus: true
+    model: 3
+
+    delegate: Text {
+        width: parent.width
+        height: 10
+        property int idx: index
+        text: index
+    }
+}

tests/auto/quick/qquicklistview/qquicklistview.pro

@@ -16,6 +16,7 @@ include (../../shared/util.pri)
 include (../shared/util.pri)
 
 TESTDATA = data/*
+DISTFILES += data/*
 
 QT += core-private gui-private qml-private quick-private testlib qmltest
 

tests/auto/quick/qquicklistview/tst_qquicklistview.cpp

@@ -166,6 +166,7 @@ private slots:
     void QTBUG_16037();
     void indexAt_itemAt_data();
     void indexAt_itemAt();
+    void itemAtIndex();
     void incrementalModel();
     void onAdd();
     void onAdd_data();
@@ -4782,6 +4783,29 @@ void tst_QQuickListView::indexAt_itemAt()
     delete testObject;
 }
 
+void tst_QQuickListView::itemAtIndex()
+{
+    QScopedPointer<QQuickView> window(createView());
+    window->setSource(testFileUrl("listview-itematindex.qml"));
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window.data()));
+
+    QQuickListView *listview = qobject_cast<QQuickListView*>(window->rootObject());
+    QVERIFY(listview != nullptr);
+
+    QCOMPARE(listview->itemAtIndex(-1), nullptr);
+    QCOMPARE(listview->itemAtIndex(3), nullptr);
+    QQuickItem *item = listview->itemAtIndex(0);
+    QVERIFY(item);
+    QCOMPARE(item->property("idx"), 0);
+    item = listview->itemAtIndex(1);
+    QVERIFY(item);
+    QCOMPARE(item->property("idx"), 1);
+    item = listview->itemAtIndex(2);
+    QVERIFY(item);
+    QCOMPARE(item->property("idx"), 2);
+}
+
 void tst_QQuickListView::incrementalModel()
 {
     QScopedPointer<QQuickView> window(createView());