addDockWidgetToContainingWindow should use the mainWindow() function to work in a non-toplevel main window

[AndreMeyerRMC]

As stated in the DockWidgetBase::mainWindow - function, The Docking system should work with QMainWindows that are children of other windows. In addDockWidgetToContainingWindow that is not recognised.

diff:

Index: src/DockWidgetBase.cpp
===================================================================
--- src/DockWidgetBase.cpp
+++ src/DockWidgetBase.cpp
@@ -118,7 +118,7 @@
                                                      DockWidgetBase *relativeTo,
                                                      InitialOption initialOption)
 {
-    if (auto mainWindow = qobject_cast<MainWindowBase *>(window())) {
+    if (auto mainWindow = DockWidgetBase::mainWindow()) {
         // It's inside a main window. Simply use the main window API.
         mainWindow->addDockWidget(other, location, relativeTo, initialOption);
         return;

[iamsergio]

Fixed for 2.1 and added a unit-test