Properly implemented support for canceling non-opaque undocking on Linux

demo/MainWindow.cpp

@@ -384,8 +384,7 @@ CMainWindow::CMainWindow(QWidget *parent) :
 
     // uncomment the follwing line if you want to use non opaque undocking and splitter
     // moevements
-    CDockManager::setConfigFlags(CDockManager::DefaultNonOpaqueConfig);
-    CDockManager::setConfigFlag(CDockManager::DragPreviewHasWindowFrame, true);
+    // CDockManager::setConfigFlags(CDockManager::DefaultNonOpaqueConfig);
 
 	// Now create the dock manager and its content
 	d->DockManager = new CDockManager(this);

src/FloatingDragPreview.cpp

@@ -206,6 +206,13 @@ CFloatingDragPreview::CFloatingDragPreview(QWidget* Content, QWidget* parent) :
 
 	connect(qApp, SIGNAL(applicationStateChanged(Qt::ApplicationState)),
 		SLOT(onApplicationStateChanged(Qt::ApplicationState)));
+
+#ifdef Q_OS_LINUX
+    // In Windows this widget directly receives the escape key press events
+    // in Linux we need to install an event filter for the given Content
+    // widget to receive the escape key press
+    Content->installEventFilter(this);
+#endif
 }
 
 
@@ -372,6 +379,23 @@ void CFloatingDragPreview::onApplicationStateChanged(Qt::ApplicationState state)
 }
 
 
+//============================================================================
+bool CFloatingDragPreview::eventFilter(QObject *watched, QEvent *event)
+{
+    if (event->type() == QEvent::KeyPress)
+    {
+        QKeyEvent* e = static_cast<QKeyEvent*>(event);
+        if (e->key() == Qt::Key_Escape)
+        {
+            d->Content->removeEventFilter(this);
+            d->cancelDragging();
+        }
+    }
+
+    return false;
+}
+
+
 
 
 } // namespace ads

src/FloatingDragPreview.h

@@ -78,6 +78,12 @@ public:
 	 */
 	~CFloatingDragPreview();
 
+    /**
+     * We filter the events of the assigned content widget to receive
+     * escape key presses for canceling the drag operation
+     */
+    virtual bool eventFilter(QObject *watched, QEvent *event) override;
+
 
 public: // implements IFloatingWidget -----------------------------------------
 	virtual void startFloating(const QPoint& DragStartMousePos, const QSize& Size,