QQuickItemView: avoid wrong repositioning of removed items

If all the items currently in the view are being removed,
lastVisibleIndex will be -1. This caused an unwanted repositioning
of all the deleted items, which got moved to a wrong location.
Therefore, when all visible items are removed, we should avoid
recomputing any item's position.

Task-number: QTBUG-57225
Change-Id: I9909748a9cccb5e6a3726306e250921ce69fcba9
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 125 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickgridview/data/qtbug57225.qml b/tests/auto/quick/qquickgridview/data/qtbug57225.qml
new file mode 100644
index 0000000000..7f5e67822c
--- /dev/null
+++ b/tests/auto/quick/qquickgridview/data/qtbug57225.qml
@@ -0,0 +1,94 @@
+import QtQuick 2.0
+
+Rectangle {
+    id: root
+    width: 200
+    height: 200
+
+    property int duration: 100
+    property int count: grid.count
+
+    Component {
+        id: myDelegate
+        Rectangle {
+            id: wrapper
+
+            property string nameData: name
+            property bool removalStarted: false
+            property real minX: 0
+            property real minY: 0
+
+            onXChanged: if (removalStarted) grid.recordPosition(x, y)
+            onYChanged: if (removalStarted) grid.recordPosition(x, y)
+
+            objectName: "wrapper"
+            width: 80
+            height: 80
+            border.width: 1
+            Column {
+                Text { text: index }
+                Text {
+                    text: wrapper.x + ", " + wrapper.y
+                }
+                Text {
+                    id: textName
+                    objectName: "textName"
+                    text: name
+                }
+            }
+            color: GridView.isCurrentItem ? "lightsteelblue" : "white"
+
+            GridView.onRemove: SequentialAnimation {
+                PropertyAction { target: wrapper; property: "removalStarted"; value: true }
+                PropertyAction { target: wrapper; property: "GridView.delayRemove"; value: true }
+                NumberAnimation { target: wrapper; property: "scale"; to: 0.5; duration: root.duration; easing.type: Easing.InOutQuad }
+                PropertyAction { target: wrapper; property: "GridView.delayRemove"; value: false }
+                PropertyAction { target: grid; property: "animationDone"; value: true }
+            }
+
+        }
+    }
+
+    GridView {
+        id: grid
+
+        property bool animationDone: false
+        property point minimumPosition: Qt.point(0, 0)
+
+        signal delegateMoved(real x, real y)
+
+        objectName: "grid"
+        focus: true
+        anchors.fill: parent
+        cacheBuffer: 0
+        cellWidth: 80
+        cellHeight: 80
+        model: testModel
+        delegate: myDelegate
+
+        displaced: Transition {
+            id: transition
+            SequentialAnimation {
+                NumberAnimation {
+                    properties: "x,y"
+                    duration: root.duration
+                    easing.type: Easing.OutBounce
+                    easing.amplitude: 10.0      // longer-lasting bounce to trigger bug
+                }
+            }
+        }
+
+        function recordPosition(index, x, y) {
+            if (x < minimumPosition.x || y < minimumPosition.y) {
+                minimumPosition = Qt.point(x, y)
+            }
+        }
+    }
+
+    Rectangle {
+        anchors.fill: grid
+        color: "lightsteelblue"
+        opacity: 0.2
+    }
+}
+
diff --git a/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp b/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp
index 2b14842658..7333cc3ceb 100644
--- a/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp
+++ b/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp
@@ -153,6 +153,7 @@ private slots:
     void multipleTransitions();
     void multipleTransitions_data();
     void multipleDisplaced();
+    void regression_QTBUG_57225();
 
     void inserted_leftToRight_RtL_TtB();
     void inserted_leftToRight_RtL_TtB_data();
@@ -5798,6 +5799,36 @@ void tst_QQuickGridView::multipleDisplaced()
     delete window;
 }
 
+void tst_QQuickGridView::regression_QTBUG_57225()
+{
+    // deleting all visible items should not cause a repositioning of said items.
+
+    QaimModel model;
+    for (int i = 0; i < 20; i++)
+        model.addItem("Original item" + QString::number(i), "");
+
+    QQuickView *window = createView();
+    QQmlContext *ctxt = window->rootContext();
+    ctxt->setContextProperty("testModel", &model);
+    window->setSource(testFileUrl("qtbug57225.qml"));
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window));
+
+    QQuickGridView *gridview = findItem<QQuickGridView>(window->rootObject(), "grid");
+    QVERIFY(gridview != 0);
+    QTRY_COMPARE(QQuickItemPrivate::get(gridview)->polishScheduled, false);
+
+    model.removeItems(0, 8);
+    QTRY_VERIFY(gridview->property("animationDone").toBool());
+
+    // verify that none of the removed items has moved to a negative position
+    QPoint minimumPosition = gridview->property("minimumPosition").toPoint();
+    QVERIFY(minimumPosition.x() >= 0);
+    QVERIFY(minimumPosition.y() >= 0);
+
+    delete window;
+}
+
 void tst_QQuickGridView::cacheBuffer()
 {
     QQuickView *window = createView();