Fix positioning issues and change content y repositioning behaviour

Refactor the code for re-positioning the visibleItems.first() in
QSGItemView::applyModelChanges() and fix various positioning issues.

The positioning behaviour for removing items at the start of the view
has  changed. This action will no longer cause the content y to move
down; previously the content y would always move down unless another
item was moving backwards to the first visible position. This will make
it easier to implement built-in removal transitions for the views, since
removed items cannot be animated if the content y jumps down past them.

Additionally, moving items from before a GridView should not cause the
top item in the view to move upwards and out of the view.

This also adds additional remove tests and fixes the
tst_QQuickGridView::moved() test which wasn't waiting for the polish
event after setting the content y, which caused some of the tests to
pass even though their test data was wrong.

Change-Id: Idad11a73a18f88208e73a52111ed839458e05f2d
Reviewed-by: Martin Jones <martin.jones@nokia.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/src/quick/items/qquickitemview_p_p.h b/src/quick/items/qquickitemview_p_p.h
index cfceca670a..a81aa6f54d 100644
--- a/src/quick/items/qquickitemview_p_p.h
+++ b/src/quick/items/qquickitemview_p_p.h
@@ -99,12 +99,13 @@ class QQuickItemViewPrivate : public QQuickFlickablePrivate
 public:
     QQuickItemViewPrivate();
 
-    struct InsertionsResult {
-        QList<FxViewItem *> addedItems;
-        QList<FxViewItem *> movedBackwards;
-        qreal sizeAddedBeforeVisible;
+    struct ChangeResult {
+        QDeclarativeNullableValue<qreal> visiblePos;
+        qreal sizeChangesBeforeVisiblePos;
+        qreal sizeChangesAfterVisiblePos;
 
-        InsertionsResult() : sizeAddedBeforeVisible(0) {}
+        ChangeResult(const QDeclarativeNullableValue<qreal> &p)
+            : visiblePos(p), sizeChangesBeforeVisiblePos(0), sizeChangesAfterVisiblePos(0) {}
     };
 
     enum BufferMode { NoBuffer = 0x00, BufferBefore = 0x01, BufferAfter = 0x02 };
@@ -145,6 +146,7 @@ public:
     void positionViewAtIndex(int index, int mode);
     void applyPendingChanges();
     bool applyModelChanges();
+    bool applyRemovalChange(const QDeclarativeChangeSet::Remove &removal, ChangeResult *changeResult, int *removedCount);
 
     void checkVisible() const;
 
@@ -236,11 +238,12 @@ protected:
     virtual void repositionPackageItemAt(QQuickItem *item, int index) = 0;
     virtual void resetItemPosition(FxViewItem *item, FxViewItem *toItem) = 0;
     virtual void resetFirstItemPosition() = 0;
-    virtual void moveItemBy(FxViewItem *item, qreal forwards, qreal backwards) = 0;
+    virtual void adjustFirstItem(qreal forwards, qreal backwards) = 0;
 
     virtual void layoutVisibleItems() = 0;
     virtual void changedVisibleIndex(int newIndex) = 0;
-    virtual bool applyInsertionChange(const QDeclarativeChangeSet::Insert &, FxViewItem *, InsertionsResult *) = 0;
+    virtual bool applyInsertionChange(const QDeclarativeChangeSet::Insert &insert, ChangeResult *changeResult, bool *newVisibleItemsFirst, QList<FxViewItem *> *newItems) = 0;
+
     virtual bool needsRefillForAddedOrRemovedIndex(int) const { return false; }
 
     virtual void initializeViewItem(FxViewItem *) {}