[Lazarus] Docking and Layout managers

[Hans-Peter Diettrich]

Mattias Gärtner schrieb:

> Maybe I misunderstood your proposal.
> What parts of TWinControl should be moved to TContainerControl?
> Do you want to move the ControlCount and Controls properties to
> TContainerControl?

Yes, all the child control related stuff. I'd move that into the 
LayoutManager, and redirect all related methods and properties to that 
helper object. Then the LayoutManager is as exchangable as the DockManager.

> What about TControl.Parent?

It will be of type TContainerControl, of course. I admit that the tests 
for TWinControl have to be revised accordingly, but there remains more 
to do. E.g. it's nonsense when TWinControl redirects docking and other 
messages to TControl, which then again delegates the job back to its own 
TWinControl parent. All that docking and child control handling stuff 
should be entirely removed from TControl, and also from TWinControl, and 
  instead should be moved into the layout and docking helper objects. 
I'm just about to find all that stuff, and to implement a direct 
connection between e.g. TDragManager, TDockPerformer, and the DockManager.

The legacy interface of all classes can survive that update, the revised 
methods only will redirect the tasks immediately to the final worker 
object. These are highly desireable changes, regardless of whether we 
introduce a new layout layer class or not. We might use conditional 
compilation, so that in case of trouble the old class tree remains 
intact, for debugging and as a last resort in case of trouble with 
legacy code.

IMO we should cut some of the old trees, in order to see the wood for 
trees again.

DoDi