Windows: Refactor code registering/unregistering drop sites.

Only top level windows of certain types should be drop sites. Add code to
update drop site registration to setParent().

This ensures the drop site is unregistered for example when winId()
is invoked on a parentless widgets which is later inserted into a layout.

Task-number: QTBUG-33635

Change-Id: Ia3161ecd59753f3f39d2a5967e9cb922cf0b9203
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

2 files changed, 43 insertions, 36 deletions

diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index e9ab902966..256967d25f 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -882,20 +882,8 @@ QWindowsWindow::QWindowsWindow(QWindow *aWindow, const QWindowsWindowData &data)
         setFlag(OpenGL_ES2);
 #endif
     }
-    if (aWindow->isTopLevel()) {
-        switch (type) {
-        case Qt::Window:
-        case Qt::Dialog:
-        case Qt::Sheet:
-        case Qt::Drawer:
-        case Qt::Popup:
-        case Qt::Tool:
-            registerDropSite();
-            break;
-        default:
-            break;
-        }
-    }
+    updateDropSite();
+
 #ifndef Q_OS_WINCE
     if (QWindowsContext::instance()->systemInfo() & QWindowsContext::SI_SupportsTouch) {
         if (QWindowsContext::user32dll.registerTouchWindow(m_data.hwnd, 0)) {
@@ -944,7 +932,7 @@ void QWindowsWindow::destroyWindow()
             context->clearWindowUnderMouse();
         if (hasMouseCapture())
             setMouseGrabEnabled(false);
-        unregisterDropSite();
+        setDropSiteEnabled(false);
 #ifdef QT_OPENGL_ES_2
         if (m_eglSurface) {
             qCDebug(lcQpaGl) << __FUNCTION__ << "Freeing EGL surface " << m_eglSurface << window();
@@ -967,31 +955,44 @@ void QWindowsWindow::destroyWindow()
     }
 }
 
-void QWindowsWindow::registerDropSite()
+void QWindowsWindow::updateDropSite()
 {
-#ifndef QT_NO_CLIPBOARD
-#  ifndef QT_NO_DRAGANDDROP
-    if (m_data.hwnd && !m_dropTarget) {
-        m_dropTarget = new QWindowsOleDropTarget(window());
-        RegisterDragDrop(m_data.hwnd, m_dropTarget);
-        CoLockObjectExternal(m_dropTarget, true, true);
+    bool enabled = false;
+    if (window()->isTopLevel()) {
+        switch (window()->type()) {
+        case Qt::Window:
+        case Qt::Dialog:
+        case Qt::Sheet:
+        case Qt::Drawer:
+        case Qt::Popup:
+        case Qt::Tool:
+            enabled = true;
+            break;
+        default:
+            break;
+        }
     }
-#  endif // !QT_NO_DRAGANDDROP
-#endif // !QT_NO_CLIPBOARD
+    setDropSiteEnabled(enabled);
 }
 
-void QWindowsWindow::unregisterDropSite()
+void QWindowsWindow::setDropSiteEnabled(bool dropEnabled)
 {
-#ifndef QT_NO_CLIPBOARD
-#  ifndef QT_NO_DRAGANDDROP
-    if (m_data.hwnd && m_dropTarget) {
+    if (isDropSiteEnabled() == dropEnabled)
+        return;
+    qCDebug(lcQpaMime) << __FUNCTION__ << window() << dropEnabled;
+#if !defined(QT_NO_CLIPBOARD) && !defined(QT_NO_DRAGANDDROP)
+    if (dropEnabled) {
+        Q_ASSERT(m_data.hwnd);
+        m_dropTarget = new QWindowsOleDropTarget(window());
+        RegisterDragDrop(m_data.hwnd, m_dropTarget);
+        CoLockObjectExternal(m_dropTarget, true, true);
+    } else {
         m_dropTarget->Release();
         CoLockObjectExternal(m_dropTarget, false, true);
         RevokeDragDrop(m_data.hwnd);
         m_dropTarget = 0;
     }
-#  endif // !QT_NO_DRAGANDDROP
-#endif // !QT_NO_CLIPBOARD
+#endif // !QT_NO_CLIPBOARD && !QT_NO_DRAGANDDROP
 }
 
 // Returns topmost QWindowsWindow ancestor even if there are embedded windows in the chain.
@@ -1188,7 +1189,7 @@ void QWindowsWindow::setParent(const QPlatformWindow *newParent)
         setParent_sys(newParent);
 }
 
-void QWindowsWindow::setParent_sys(const QPlatformWindow *parent) const
+void QWindowsWindow::setParent_sys(const QPlatformWindow *parent)
 {
     // Use GetAncestor instead of GetParent, as GetParent can return owner window for toplevels
     HWND oldParentHWND = GetAncestor(m_data.hwnd, GA_PARENT);
@@ -1217,8 +1218,11 @@ void QWindowsWindow::setParent_sys(const QPlatformWindow *parent) const
         // WS_CHILD/WS_POPUP must be manually set/cleared in addition
         // to dialog frames, etc (see  SetParent() ) if the top level state changes.
         // Force toplevel state as QWindow::isTopLevel cannot be relied upon here.
-        if (wasTopLevel != isTopLevel)
+        if (wasTopLevel != isTopLevel) {
+            setDropSiteEnabled(false);
             setWindowFlags_sys(window()->flags(), unsigned(isTopLevel ? WindowCreationData::ForceTopLevel : WindowCreationData::ForceChild));
+            updateDropSite();
+        }
     }
 }
 
@@ -1458,8 +1462,10 @@ void QWindowsWindow::setWindowFlags(Qt::WindowFlags flags)
     const QRect oldGeometry = geometry();
     if (m_data.flags != flags) {
         m_data.flags = flags;
-        if (m_data.hwnd)
+        if (m_data.hwnd) {
             m_data = setWindowFlags_sys(flags);
+            updateDropSite();
+        }
     }
     // When switching to a frameless window, geometry
     // may change without a WM_MOVE. Report change manually.
diff --git a/src/plugins/platforms/windows/qwindowswindow.h b/src/plugins/platforms/windows/qwindowswindow.h
index 99c5761a65..1d515fd2fe 100644
--- a/src/plugins/platforms/windows/qwindowswindow.h
+++ b/src/plugins/platforms/windows/qwindowswindow.h
@@ -278,11 +278,12 @@ private:
     inline QWindowsWindowData setWindowFlags_sys(Qt::WindowFlags wt, unsigned flags = 0) const;
     inline bool isFullScreen_sys() const;
     inline void setWindowState_sys(Qt::WindowState newState);
-    inline void setParent_sys(const QPlatformWindow *parent) const;
+    inline void setParent_sys(const QPlatformWindow *parent);
     inline void updateTransientParent() const;
     void destroyWindow();
-    void registerDropSite();
-    void unregisterDropSite();
+    inline bool isDropSiteEnabled() const { return m_dropTarget != 0; }
+    void setDropSiteEnabled(bool enabled);
+    void updateDropSite();
     void handleGeometryChange();
     void handleWindowStateChange(Qt::WindowState state);
     inline void destroyIcon();