GridView should re-layout if add/remove before visible index

Unlike ListView, GridView must redo its layout if an item is added or
removed from before the visible items, since it affects the column/row
layout.

Task-number: QTBUG-21588
Change-Id: Id333bc653033751c45d127973e94fae4580c55b0
Reviewed-by: Bea Lam <bea.lam@nokia.com>

3 files changed, 20 insertions, 8 deletions

diff --git a/src/declarative/items/qquickgridview.cpp b/src/declarative/items/qquickgridview.cpp
index 2793032a48..a4133143ea 100644
--- a/src/declarative/items/qquickgridview.cpp
+++ b/src/declarative/items/qquickgridview.cpp
@@ -182,6 +182,7 @@ public:
     virtual void setPosition(qreal pos);
     virtual void layoutVisibleItems();
     bool applyInsertionChange(const QDeclarativeChangeSet::Insert &, FxViewItem *, InsertionsResult *);
+    virtual bool needsRefillForAddedOrRemovedIndex(int index) const;
 
     virtual qreal headerSize() const;
     virtual qreal footerSize() const;
@@ -1853,6 +1854,13 @@ bool QQuickGridViewPrivate::applyInsertionChange(const QDeclarativeChangeSet::In
     return insertResult->addedItems.count() > prevAddedCount;
 }
 
+bool QQuickGridViewPrivate::needsRefillForAddedOrRemovedIndex(int modelIndex) const
+{
+    // If we add or remove items before visible items, a layout may be
+    // required to ensure item 0 is in the first column.
+    return modelIndex < visibleIndex;
+}
+
 /*!
     \qmlmethod QtQuick2::GridView::positionViewAtIndex(int index, PositionMode mode)
 
diff --git a/src/declarative/items/qquickitemview.cpp b/src/declarative/items/qquickitemview.cpp
index 923db4747a..79787d777c 100644
--- a/src/declarative/items/qquickitemview.cpp
+++ b/src/declarative/items/qquickitemview.cpp
@@ -1413,7 +1413,7 @@ bool QQuickItemViewPrivate::applyModelChanges()
     moveReason = QQuickItemViewPrivate::Other;
 
     int prevCount = itemCount;
-    bool removedVisible = false;
+    bool visibleAffected = false;
     bool viewportChanged = !currentChanges.pendingChanges.removes().isEmpty()
             || !currentChanges.pendingChanges.inserts().isEmpty();
 
@@ -1432,8 +1432,8 @@ bool QQuickItemViewPrivate::applyModelChanges()
             FxViewItem *item = *it;
             if (item->index == -1 || item->index < removals[i].index) {
                 // already removed, or before removed items
-                if (item->index < removals[i].index && !removedVisible)
-                    removedVisible = true;
+                if (!visibleAffected && item->index < removals[i].index)
+                    visibleAffected = true;
                 ++it;
             } else if (item->index >= removals[i].index + removals[i].count) {
                 // after removed items
@@ -1441,7 +1441,7 @@ bool QQuickItemViewPrivate::applyModelChanges()
                 ++it;
             } else {
                 // removed item
-                removedVisible = true;
+                visibleAffected = true;
                 if (!removals[i].isMove())
                     item->attached->emitRemove();
 
@@ -1463,20 +1463,22 @@ bool QQuickItemViewPrivate::applyModelChanges()
                 }
             }
         }
-
+        if (!visibleAffected && needsRefillForAddedOrRemovedIndex(removals[i].index))
+            visibleAffected = true;
     }
     if (!removals.isEmpty())
         updateVisibleIndex();
 
     const QVector<QDeclarativeChangeSet::Insert> &insertions = currentChanges.pendingChanges.inserts();
-    bool addedVisible = false;
     InsertionsResult insertResult;
     bool allInsertionsBeforeVisible = true;
 
     for (int i=0; i<insertions.count(); i++) {
         bool wasEmpty = visibleItems.isEmpty();
         if (applyInsertionChange(insertions[i], firstVisible, &insertResult))
-            addedVisible = true;
+            visibleAffected = true;
+        if (!visibleAffected && needsRefillForAddedOrRemovedIndex(insertions[i].index))
+            visibleAffected = true;
         if (insertions[i].index >= visibleIndex)
             allInsertionsBeforeVisible = false;
         if (wasEmpty && !visibleItems.isEmpty())
@@ -1542,7 +1544,8 @@ bool QQuickItemViewPrivate::applyModelChanges()
     if (prevCount != itemCount)
         emit q->countChanged();
 
-    bool visibleAffected = removedVisible || addedVisible || !currentChanges.pendingChanges.changes().isEmpty();
+    if (!visibleAffected)
+        visibleAffected = !currentChanges.pendingChanges.changes().isEmpty();
     if (!visibleAffected && viewportChanged)
         updateViewport();
 
diff --git a/src/declarative/items/qquickitemview_p_p.h b/src/declarative/items/qquickitemview_p_p.h
index 398de84c25..ca4c0ceba9 100644
--- a/src/declarative/items/qquickitemview_p_p.h
+++ b/src/declarative/items/qquickitemview_p_p.h
@@ -240,6 +240,7 @@ protected:
     virtual void layoutVisibleItems() = 0;
     virtual void changedVisibleIndex(int newIndex) = 0;
     virtual bool applyInsertionChange(const QDeclarativeChangeSet::Insert &, FxViewItem *, InsertionsResult *) = 0;
+    virtual bool needsRefillForAddedOrRemovedIndex(int) const { return false; }
 
     virtual void initializeViewItem(FxViewItem *) {}
     virtual void initializeCurrentItem() {}