How to create a custom container (like QMainWindow) designable in Designer?

[Sauntor]

I want to create a custom widget with some predefined children, and a centralWidget for derived classes to put other widgets in.
I tried, but you can drag and drop child widget everywhere in the designer! How to make children dragable only in the centralWidget's aera? What's more, how if I want a more dockWidget area?

So, what's the solution? Help!

[Pl45m4]

@Sauntor

centralWidget is only the pre-defined objectname for the default content (widget) of a QMainWindow, which is a QWidget itself.
What's wrong with using the basic QMainWindow?!
Especially using QtDesigner only, it will be hard to implement your idea.

I tried, but you can drag and drop child widget everywhere in the designer! How to make children dragable only in the centralWidget's aera?

That sounds like QtDesigner specific design-mode behavior and not how the widget behaves at runtime.
I'm thinking of a modified QtDesigner with a designer plugin for your widget... but why?!