Fix flicker when changing ListView currentIndex with VisualItemModel.

Return the Referenced flag when the view has outstanding references
otherwise it will attempt to hide an item if believes shouldn't be
visible.

Task-number: QTBUG-25849
Change-Id: I7387ab8322a1cd7f3386685086b2b8ad10c8b4f0
Reviewed-by: Bea Lam <bea.lam@nokia.com>

3 files changed, 102 insertions, 2 deletions

diff --git a/src/quick/items/qquickvisualitemmodel.cpp b/src/quick/items/qquickvisualitemmodel.cpp
index 1cefcb4ce9..1cb595ec4d 100644
--- a/src/quick/items/qquickvisualitemmodel.cpp
+++ b/src/quick/items/qquickvisualitemmodel.cpp
@@ -192,8 +192,10 @@ QQuickItem *QQuickVisualItemModel::item(int index, bool)
     Q_D(QQuickVisualItemModel);
     QQuickVisualItemModelPrivate::Item &item = d->children[index];
     item.addRef();
-    emit initItem(index, item.item);
-    emit createdItem(index, item.item);
+    if (item.ref == 1) {
+        emit initItem(index, item.item);
+        emit createdItem(index, item.item);
+    }
     return item.item;
 }
 
@@ -205,6 +207,8 @@ QQuickVisualModel::ReleaseFlags QQuickVisualItemModel::release(QQuickItem *item)
         if (d->children[idx].deref()) {
             // XXX todo - the original did item->scene()->removeItem().  Why?
             item->setParentItem(0);
+        } else {
+            return QQuickVisualModel::Referenced;
         }
     }
     return 0;
diff --git a/tests/auto/quick/qquicklistview/data/itemlist-flicker.qml b/tests/auto/quick/qquicklistview/data/itemlist-flicker.qml
new file mode 100644
index 0000000000..c0cc807bc0
--- /dev/null
+++ b/tests/auto/quick/qquicklistview/data/itemlist-flicker.qml
@@ -0,0 +1,46 @@
+// This example demonstrates placing items in a view using
+// a VisualItemModel
+
+import QtQuick 2.0
+
+Rectangle {
+    color: "lightgray"
+    width: 240
+    height: 320
+
+    VisualItemModel {
+        id: itemModel
+        objectName: "itemModel"
+        Rectangle {
+            objectName: "item1"
+            height: view.height / 3
+            width: view.width; color: "#FFFEF0"
+            Text { objectName: "text1"; text: "index: " + parent.VisualItemModel.index; font.bold: true; anchors.centerIn: parent }
+        }
+        Rectangle {
+            objectName: "item2"
+            height: view.height / 3
+            width: view.width; color: "#F0FFF7"
+            Text { objectName: "text2"; text: "index: " + parent.VisualItemModel.index; font.bold: true; anchors.centerIn: parent }
+        }
+        Rectangle {
+            objectName: "item3"
+            height: view.height / 3
+            width: view.width; color: "#F4F0FF"
+            Text { objectName: "text3"; text: "index: " + parent.VisualItemModel.index; font.bold: true; anchors.centerIn: parent }
+        }
+    }
+
+    ListView {
+        id: view
+        objectName: "view"
+        anchors.fill: parent
+        anchors.bottomMargin: 30
+        model: itemModel
+        preferredHighlightBegin: 0
+        preferredHighlightEnd: 0
+        highlightRangeMode: "StrictlyEnforceRange"
+        orientation: ListView.Vertical
+        flickDeceleration: 2000
+    }
+}
diff --git a/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp b/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
index 8d4453a6e0..45337e2814 100644
--- a/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
+++ b/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
@@ -126,6 +126,7 @@ private slots:
     void insertBeforeVisible_data();
     void swapWithFirstItem();
     void itemList();
+    void itemListFlicker();
     void currentIndex_delayedItemCreation();
     void currentIndex_delayedItemCreation_data();
     void currentIndex();
@@ -2642,6 +2643,55 @@ void tst_QQuickListView::itemList()
     delete canvas;
 }
 
+void tst_QQuickListView::itemListFlicker()
+{
+    QQuickView *canvas = createView();
+    canvas->setSource(testFileUrl("itemlist-flicker.qml"));
+    canvas->show();
+    qApp->processEvents();
+
+    QQuickListView *listview = findItem<QQuickListView>(canvas->rootObject(), "view");
+    QTRY_VERIFY(listview != 0);
+
+    QQuickItem *contentItem = listview->contentItem();
+    QTRY_VERIFY(contentItem != 0);
+
+    QQuickVisualItemModel *model = canvas->rootObject()->findChild<QQuickVisualItemModel*>("itemModel");
+    QTRY_VERIFY(model != 0);
+
+    QTRY_VERIFY(model->count() == 3);
+    QTRY_COMPARE(listview->currentIndex(), 0);
+
+    QQuickItem *item;
+
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item1"));
+    QVERIFY(item->isVisible());
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item2"));
+    QVERIFY(item->isVisible());
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item3"));
+    QVERIFY(item->isVisible());
+
+    listview->setCurrentIndex(1);
+
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item1"));
+    QVERIFY(item->isVisible());
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item2"));
+    QVERIFY(item->isVisible());
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item3"));
+    QVERIFY(item->isVisible());
+
+    listview->setCurrentIndex(2);
+
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item1"));
+    QVERIFY(item->isVisible());
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item2"));
+    QVERIFY(item->isVisible());
+    QVERIFY(item = findItem<QQuickItem>(contentItem, "item3"));
+    QVERIFY(item->isVisible());
+
+    delete canvas;
+}
+
 void tst_QQuickListView::cacheBuffer()
 {
     QQuickView *canvas = createView();