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Re: Understanding Frames [message #3917 is a reply to message #3863]

Sun, 09 July 2006 15:53

mirek
Messages: 13980
Registered: November 2005

Ultimate Member

OK, here is a simple way how to undestand frames:

Frames emerged to solve the simple problem: You have some widget that has scroll-bar(s). Now the question is how to organize all things.

Without frames, you would need to use some sort of composition: One "parent" Ctrl, which would provide some sort of static edge, scroll-bar widget and "view" widget.

Unfortunate thing about this arrangement is that "view" widget becomes "contained" inside parent Ctrl, but in dialog you need to work with parent Ctrl. So it is e.g. difficult to create subclass of such view.

Solution: scroll-bar is "frame". You can freely add frames to Ctrl and the important thing about them is that they "reduce" the view area. With this concept, you can even make that static edge a frame. Moreover, you can alter existing widgets by adding further frames (e.g., you can add HeaderCtrl to LineEdit etc...)

There are things to remember

- frames do not have to be widgets, but can be. E.g. ScrollBar is derived both from Ctrl and Frame. Means you can add it to widget either as regular child, or using AddFrame.

- CtrlFrame interface is designed in a way that makes possible to use single static frame instance for multiple widget.

Mirek

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