Dragging QDockWidgets between QMainWindows

Question

I have a question regarding dragging QDockWidgets between QMainWindows. I have an application with different "DockAreas" which have a QMainWindow member with one or more QDockWidgets. Additionally, I want to make QDockWidgets drag-and-droppable into other, already floating QDockWidgets (not tabbed!).

To have the nice hover-effect upon drag-and-drop, the floating QDockWidgets are embedded in a new instance of my DockArea with the QMainWindow member. Now I intercept the mousemove event of the dragged QDockWidget and change its parent when it hovers over another QMainWindow of my DockArea. Unfortunately, this causes a crash and it looks like the original QLayoutItem, where this QDockWidget was in, is gone.

void QDockWidgetPrivate::moveEvent(QMoveEvent *event)
{
    // ...
    // now this widgetItem member of state is kaputt
    layout->hover(state->widgetItem, globalMousePos);
}

I found different suggestions for dragging-dropping QDockWidgets between QMainWindows on the internet:

1) Re-parenting - that's what I am trying atm

2) QDrag - did not work for me, async exec() breaks my application and at the end I have to reparent anyway

3) Call addDockWidget(...) of the new QMainWindow - docks the QDockWidget and I would have to make it floating again and somehow "continue the dragging"

I am open to any new suggestions :) Thank you in advance!

Answer 1

I'm wrestling with the same Problem right now and want to share.

Ich found this forum post dealing with the same problem: http://www.qtcentre.org/threads/41847-Dragging-QDockWidgets-between-QMainWindows This solution is however flawed: it doesn't work properly if you allow the Dockables to be floating. And the enterEvent does not actually trigger when you enter the other window and still dragging the QDockWidget. It only triggers after release.

I'm also going for the reparenting (1). QDrag seems problematic when you also want to allow rearranging the QDockWidget within the Window.

I think one would correctly do this by reacting to the drop/release of the dragged QDockWidget. But I can't find an event or signal for this.