Fixed the QTreeView expansion/collpasing when animated

If you had a QTreeView with expandable items, if you tried to expand and while
the animation was still running you'd try to collpase the node,
the display would be completely broken: the items below that items would
not be visible any more except for a fraction of a second when expanding
or collapsing it again.
The problem is in the fact that when starting an animation the QTreeView
stores the state before animating. And it does that even if an animation
is already running. So the stateBeforeAnimation becomes AnimatingState and
when the animation finishes, AnimatingState is the state that is restored
breaking the painting.
Unit test is included.

qtbase-sha1: 1e97dbaf6ca807397e3ec77a3611763769499d17
Change-Id: I62e16101b70153f78022f6195fd9de6db0cd4878
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

2 files changed, 47 insertions, 2 deletions

diff --git a/src/gui/itemviews/qtreeview.cpp b/src/gui/itemviews/qtreeview.cpp
index bc9d54c482..40234e0b6b 100644
--- a/src/gui/itemviews/qtreeview.cpp
+++ b/src/gui/itemviews/qtreeview.cpp
@@ -2884,7 +2884,9 @@ void QTreeViewPrivate::expand(int item, bool emitSignal)
     if (emitSignal && animationsEnabled)
         prepareAnimatedOperation(item, QVariantAnimation::Forward);
 #endif //QT_NO_ANIMATION
-    stateBeforeAnimation = state;
+     //if already animating, stateBeforeAnimation is set to the correct value
+    if (state != QAbstractItemView::AnimatingState)
+        stateBeforeAnimation = state;
     q->setState(QAbstractItemView::ExpandingState);
     const QModelIndex index = viewItems.at(item).index;
     storeExpanded(index);
@@ -2975,7 +2977,9 @@ void QTreeViewPrivate::collapse(int item, bool emitSignal)
         prepareAnimatedOperation(item, QVariantAnimation::Backward);
 #endif //QT_NO_ANIMATION
 
-    stateBeforeAnimation = state;
+    //if already animating, stateBeforeAnimation is set to the correct value
+    if (state != QAbstractItemView::AnimatingState)
+        stateBeforeAnimation = state;
     q->setState(QAbstractItemView::CollapsingState);
     expandedIndexes.erase(it);
     viewItems[item].expanded = false;
diff --git a/tests/auto/qtreeview/tst_qtreeview.cpp b/tests/auto/qtreeview/tst_qtreeview.cpp
index 7ef5406547..716fbd523a 100644
--- a/tests/auto/qtreeview/tst_qtreeview.cpp
+++ b/tests/auto/qtreeview/tst_qtreeview.cpp
@@ -76,8 +76,11 @@ static void initStandardTreeModel(QStandardItemModel *model)
     model->insertRow(2, item);
 }
 
+class tst_QTreeView;
 struct PublicView : public QTreeView
 {
+    friend class tst_QTreeView;
+
     inline void executeDelayedItemsLayout()
     { QTreeView::executeDelayedItemsLayout(); }
 
@@ -246,6 +249,10 @@ private slots:
     void taskQTBUG_11466_keyboardNavigationRegression();
     void taskQTBUG_13567_removeLastItemRegression();
     void taskQTBUG_25333_adjustViewOptionsForIndex();
+
+#ifndef QT_NO_ANIMATION
+    void quickExpandCollapse();
+#endif
 };
 
 class QtTestModel: public QAbstractItemModel
@@ -4050,6 +4057,40 @@ void tst_QTreeView::taskQTBUG_25333_adjustViewOptionsForIndex()
 
 }
 
+#ifndef QT_NO_ANIMATION
+void tst_QTreeView::quickExpandCollapse()
+{
+    //this unit tests makes sure the state after the animation is restored correctly
+    //after starting a 2nd animation while the first one was still on-going
+    //this tests that the stateBeforeAnimation is not set to AnimatingState
+    PublicView tree;
+    tree.setAnimated(true);
+    QStandardItemModel model;
+    QStandardItem *root = new QStandardItem("root");
+    root->appendRow(new QStandardItem("subnode"));
+    model.appendRow(root);
+    tree.setModel(&model);
+
+    QModelIndex rootIndex = root->index();
+    QVERIFY(rootIndex.isValid());
+
+    tree.show();
+    QTest::qWaitForWindowShown(&tree);
+
+    int initialState = tree.state();
+
+    tree.expand(rootIndex);
+    QCOMPARE(tree.state(), (int)PublicView::AnimatingState);
+
+    tree.collapse(rootIndex);
+    QCOMPARE(tree.state(), (int)PublicView::AnimatingState);
+
+    QTest::qWait(500); //the animation lasts for 250ms max so 500 should be enough
+
+    QCOMPARE(tree.state(), initialState);
+}
+#endif
+
 
 QTEST_MAIN(tst_QTreeView)
 #include "tst_qtreeview.moc"