Added a new event type, WinIdChange.

This is sent to a native widget when its window system identifer has
changed.

This is motivated by the fact that, on Symbian, the native window
system identifier may change in situations other than a change of
parent widget.  Specifically, calling QWidget::setParent, passing in
the widget's existing parent, but OR-in Qt::Window into the window
flags, causes a new native window handle to be created.  Furthermore,
because of the fact that Symbian does not allow existing windows to be
reparented, any descendents of the original widget which are also
native, must also be given new window system handles.

Note that setWinId does not send a WinIdChange event if the incoming
winId is zero.  This is because setWinId(0) is only called in two
situations:
1. During native widget destruction
2. During re-creation of the winId for a native widget

Task-number: QTBUG-4664
Reviewed-by: Bjoern Erik Nilsen

3 files changed, 17 insertions, 2 deletions

diff --git a/src/corelib/kernel/qcoreevent.cpp b/src/corelib/kernel/qcoreevent.cpp
index 744e6a9..44a354b 100644
--- a/src/corelib/kernel/qcoreevent.cpp
+++ b/src/corelib/kernel/qcoreevent.cpp
@@ -228,6 +228,7 @@ QT_BEGIN_NAMESPACE
     \value TouchBegin                       Beginning of a sequence of touch-screen and/or track-pad events (QTouchEvent)
     \value TouchUpdate                      Touch-screen event (QTouchEvent)
     \value TouchEnd                         End of touch-event sequence (QTouchEvent)
+    \value WinIdChange                      The window system identifer for this native widget has changed
 
     User events should have values between \c User and \c{MaxUser}:
 
diff --git a/src/corelib/kernel/qcoreevent.h b/src/corelib/kernel/qcoreevent.h
index d66cead..99280d3 100644
--- a/src/corelib/kernel/qcoreevent.h
+++ b/src/corelib/kernel/qcoreevent.h
@@ -283,6 +283,8 @@ public:
 
         UpdateSoftKeys = 201,                   // Internal for compressing soft key updates
 
+        WinIdChange = 203,
+
         // 512 reserved for Qt Jambi's MetaCall event
         // 513 reserved for Qt Jambi's DeleteOnMainThread event
 
diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 4cbf762..7c11c00 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -1502,6 +1502,8 @@ void QWidgetPrivate::setWinId(WId id)                // set widget identifier
         mapper->remove(data.winid);
     }
 
+    const WId oldWinId = data.winid;
+
     data.winid = id;
 #if defined(Q_WS_X11)
     hd = id; // X11: hd == ident
@@ -1509,6 +1511,16 @@ void QWidgetPrivate::setWinId(WId id)                // set widget identifier
     if (mapper && id && !userDesktopWidget) {
         mapper->insert(data.winid, q);
     }
+
+    if(oldWinId != id) {
+        // Do not emit an event when the old winId is destroyed.  This only
+        // happens (a) during widget destruction, and (b) immediately prior
+        // to creation of a new winId, for example as a result of re-parenting.
+        if(id != 0) {
+            QEvent e(QEvent::WinIdChange);
+            QCoreApplication::sendEvent(q, &e);
+        }
+    }
 }
 
 void QWidgetPrivate::createTLExtra()
@@ -2227,8 +2239,8 @@ QWidget *QWidget::find(WId id)
     against. If Qt is using Carbon, the {WId} is actually an HIViewRef. If Qt
     is using Cocoa, {WId} is a pointer to an NSView.
 
-    \note We recommend that you do not store this value as it is likely to
-    change at run-time.
+    This value may change at run-time. An event with type QEvent::WinIdChange
+    will be sent to the widget following a change in window system identifier.
 
     \sa find()
 */