Fixed defect in handling of expose events for Symbian

Commit bc82db did not correctly handle native child widgets.

Consider the case when we have a top-level widget A with a native
child widget B.  When QSymbianControl::Draw() is called on the
control corresponding to B, the following occurs:
    1. The inExpose flag is set in B's QWExtra structure.
    2. The call to syncBackingStore() results in a call to
       QWidgetBackingStore::flush(), passing default parameters.
    3. Because no target widget was passed to flush(), this
       function selects the top-level widget (A) as the target for
       the flush operation, passing A as the first argument of
       QS60WindowSurface::flush().
    4. QS60WindowSurface::flush() checks the inExpose flag from A's
       QWExtra structure, finds it to be false, and proceeds to
       call DrawNow() on A's control.

Because QSymbianControl::Draw() uses the default graphics context,
this context is shared between controls.  This means that the DrawNow()
call in step 4 causes a WSERV-10 panic (Activate() called on an
already-active) graphics context.

This patch moves the inExpose flag from B's QWExtra into A's QTLWExtra,
with the result that the call to DrawNow() in step 4 is suppressed.

Task-number: QTBUG-7960
Reviewed-by: axis

1 files changed, 7 insertions, 4 deletions

diff --git a/src/gui/painting/qwindowsurface_s60.cpp b/src/gui/painting/qwindowsurface_s60.cpp
index b41dc2c..6cbf3d9 100644
--- a/src/gui/painting/qwindowsurface_s60.cpp
+++ b/src/gui/painting/qwindowsurface_s60.cpp
@@ -145,12 +145,15 @@ QImage* QS60WindowSurface::buffer(const QWidget *widget)
 
 void QS60WindowSurface::flush(QWidget *widget, const QRegion &region, const QPoint &)
 {
-    QWExtra *extra = widget->d_func()->extraData();
-    if (extra && !extra->inExpose) {
-        extra->inExpose = true; // Prevent DrawNow() from calling syncBackingStore() again
+    QWidget *window = widget->window();
+    Q_ASSERT(window);
+    QTLWExtra *topExtra = window->d_func()->maybeTopData();
+    Q_ASSERT(topExtra);
+    if (!topExtra->inExpose) {
+        topExtra->inExpose = true; // Prevent DrawNow() from calling syncBackingStore() again
         TRect tr = qt_QRect2TRect(region.boundingRect());
         widget->winId()->DrawNow(tr);
-        extra->inExpose = false;
+        topExtra->inExpose = false;
     }
 }