Don't recreate header and footer unnecessarily

The only time that they need to be recreated is if the orientation
changes (even then, a good implementation could handle it, but no
point requiring that now).

Task-number: QTBUG-40375
Change-Id: Id0215fb812724827bb139cda8f8dc6208c703852
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>

4 files changed, 11 insertions, 9 deletions

diff --git a/src/quick/items/qquickgridview.cpp b/src/quick/items/qquickgridview.cpp
index d5ca3a128e..c9a051c9bb 100644
--- a/src/quick/items/qquickgridview.cpp
+++ b/src/quick/items/qquickgridview.cpp
@@ -1616,7 +1616,7 @@ void QQuickGridView::setFlow(Flow flow)
         }
         setContentX(0);
         setContentY(0);
-        d->regenerate();
+        d->regenerate(true);
         emit flowChanged();
     }
 }
diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index 94abbd0954..ff8c69a9c0 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -1783,18 +1783,20 @@ void QQuickItemViewPrivate::refill(qreal from, qreal to)
         emit q->countChanged();
 }
 
-void QQuickItemViewPrivate::regenerate()
+void QQuickItemViewPrivate::regenerate(bool orientationChanged)
 {
     Q_Q(QQuickItemView);
     if (q->isComponentComplete()) {
         currentChanges.reset();
-        delete header;
-        header = 0;
-        delete footer;
-        footer = 0;
+        if (orientationChanged) {
+            delete header;
+            header = 0;
+            delete footer;
+            footer = 0;
+        }
+        clear();
         updateHeader();
         updateFooter();
-        clear();
         updateViewport();
         setPosition(contentStartOffset());
         refill();
diff --git a/src/quick/items/qquickitemview_p_p.h b/src/quick/items/qquickitemview_p_p.h
index a0d17b3bf9..297b9a1471 100644
--- a/src/quick/items/qquickitemview_p_p.h
+++ b/src/quick/items/qquickitemview_p_p.h
@@ -184,7 +184,7 @@ public:
     virtual void clear();
     virtual void updateViewport();
 
-    void regenerate();
+    void regenerate(bool orientationChanged=false);
     void layout();
     virtual void animationFinished(QAbstractAnimationJob *);
     void refill();
diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp
index c496eab3c5..e5b9f9cf59 100644
--- a/src/quick/items/qquicklistview.cpp
+++ b/src/quick/items/qquicklistview.cpp
@@ -2070,7 +2070,7 @@ void QQuickListView::setOrientation(QQuickListView::Orientation orientation)
             setFlickableDirection(HorizontalFlick);
             setContentY(0);
         }
-        d->regenerate();
+        d->regenerate(true);
         emit orientationChanged();
     }
 }