Fix potential use of incorrect bounds in delegate tracking.

Using GridView.SnapToRow and GridView.ApplyRange with a top margin
could lead to the view jumping (rather than smoothly transitioning)
when changing the currentIndex.

Change-Id: I6936b378220f59e8d416f7531cf8b6906c723cb2
Task-number: QTBUG-45640
Reviewed-by: Martin Jones <martin.jones@qinetic.com.au>

4 files changed, 78 insertions, 14 deletions

diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index 7a55bd6e0a..d4c8c3f8ee 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -910,11 +910,7 @@ void QQuickItemViewPrivate::positionViewAtIndex(int index, int mode)
 
     qreal pos = isContentFlowReversed() ? -position() - size() : position();
     FxViewItem *item = visibleItem(idx);
-    qreal maxExtent;
-    if (layoutOrientation() == Qt::Vertical)
-        maxExtent = isContentFlowReversed() ? q->minYExtent()-size(): -q->maxYExtent();
-    else
-        maxExtent = isContentFlowReversed() ? q->minXExtent()-size(): -q->maxXExtent();
+    qreal maxExtent = calculatedMaxExtent();
     if (!item) {
         qreal itemPos = positionAt(idx);
         changedVisibleIndex(idx);
@@ -960,11 +956,7 @@ void QQuickItemViewPrivate::positionViewAtIndex(int index, int mode)
             break;
         }
         pos = qMin(pos, maxExtent);
-        qreal minExtent;
-        if (layoutOrientation() == Qt::Vertical)
-            minExtent = isContentFlowReversed() ? q->maxYExtent()-size(): -q->minYExtent();
-        else
-            minExtent = isContentFlowReversed() ? q->maxXExtent()-size(): -q->minXExtent();
+        qreal minExtent = calculatedMinExtent();
         pos = qMax(pos, minExtent);
         moveReason = QQuickItemViewPrivate::Other;
         q->cancelFlick();
@@ -1135,6 +1127,29 @@ qreal QQuickItemViewPrivate::maxExtentForAxis(const AxisData &axisData, bool for
     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;
+}
+
 // for debugging only
 void QQuickItemViewPrivate::checkVisible() const
 {
@@ -1282,10 +1297,12 @@ void QQuickItemView::trackedPositionChanged()
             if (trackedPos < pos + d->highlightRangeStart)
                 pos = trackedPos - d->highlightRangeStart;
             if (d->highlightRange != StrictlyEnforceRange) {
-                if (pos > d->endPosition() - d->size())
-                    pos = d->endPosition() - d->size();
-                if (pos < d->startPosition())
-                    pos = d->startPosition();
+                qreal maxExtent = d->calculatedMaxExtent();
+                if (pos > maxExtent)
+                    pos = maxExtent;
+                qreal minExtent = d->calculatedMinExtent();
+                if (pos < minExtent)
+                    pos = minExtent;
             }
         } else {
             if (d->trackedItem != d->currentItem) {
diff --git a/src/quick/items/qquickitemview_p_p.h b/src/quick/items/qquickitemview_p_p.h
index 67ef413d31..f535963fdb 100644
--- a/src/quick/items/qquickitemview_p_p.h
+++ b/src/quick/items/qquickitemview_p_p.h
@@ -200,6 +200,8 @@ public:
 
     qreal minExtentForAxis(const AxisData &axisData, bool forXAxis) const;
     qreal maxExtentForAxis(const AxisData &axisData, bool forXAxis) const;
+    qreal calculatedMinExtent() const;
+    qreal calculatedMaxExtent() const;
 
     void applyPendingChanges();
     bool applyModelChanges(ChangeResult *insertionResult, ChangeResult *removalResult);
diff --git a/tests/auto/quick/qquickgridview/data/qtbug45640.qml b/tests/auto/quick/qquickgridview/data/qtbug45640.qml
new file mode 100644
index 0000000000..6973773432
--- /dev/null
+++ b/tests/auto/quick/qquickgridview/data/qtbug45640.qml
@@ -0,0 +1,24 @@
+import QtQuick 2.0
+
+GridView {
+    id: gridView
+    width: 400; height: 400
+    cellHeight: 100
+    cellWidth: 100
+    model: 32
+
+    topMargin: 50
+    snapMode: GridView.SnapToRow
+    preferredHighlightBegin: 50
+    preferredHighlightEnd: 50
+    highlightRangeMode: GridView.ApplyRange
+
+    delegate: Rectangle {
+        width: 100
+        height: 100
+        color: index % 2 == 0 ? "#FFFF00" : "#0000FF"
+    }
+
+    highlight: Rectangle { color: "red"; z: 2 }
+    highlightMoveDuration: 1000
+}
diff --git a/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp b/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp
index d53ee00b45..b8ad1948ed 100644
--- a/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp
+++ b/tests/auto/quick/qquickgridview/tst_qquickgridview.cpp
@@ -209,6 +209,8 @@ private slots:
     void contentHeightWithDelayRemove_data();
     void contentHeightWithDelayRemove();
 
+    void QTBUG_45640();
+
 private:
     QList<int> toIntList(const QVariantList &list);
     void matchIndexLists(const QVariantList &indexLists, const QList<int> &expectedIndexes);
@@ -6542,6 +6544,25 @@ void tst_QQuickGridView::contentHeightWithDelayRemove()
     delete window;
 }
 
+void tst_QQuickGridView::QTBUG_45640()
+{
+    QQuickView *window = createView();
+    window->setSource(testFileUrl("qtbug45640.qml"));
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window));
+
+    QQuickGridView *gridview = qobject_cast<QQuickGridView*>(window->rootObject());
+    QVERIFY(gridview != 0);
+
+    QCOMPARE(gridview->contentY(), qreal(-50.0));
+
+    gridview->moveCurrentIndexDown();
+
+    QTRY_VERIFY(gridview->contentY() > qreal(-50.0) && gridview->contentY() < qreal(0.0));
+
+    delete window;
+}
+
 QTEST_MAIN(tst_QQuickGridView)
 
 #include "tst_qquickgridview.moc"