[Lazarus] Message dialogs in Lazarus

Hans-Peter Diettrich DrDiettrich1 at aol.com
Mon Dec 20 17:19:32 CET 2010

Darius Blaszyk schrieb:

> - implement a basic layout manager. While you're at it could you also
> integrate it with the design editor? It will make our lives more easy.

There exist already a couple of layout managers in the LCL, but they are 
totally isolated. It had been easy with the recent AutoSize rewrite to 
implement a general layout manager interface. Since ChildSizing is 
already a link to an external object, it could have been extended into a 
more general layout manager link as well.

There is nothing magic with layout managers, they have to do nothing but 
arrange their child controls, and to report the minimal and desired 
sizes to their parent (with AutoSize). Every docking manager already is 
a layout manager for its site, and its interface only lacks 
beforementioned AutoSize capabilities.

> Once you have done all this, and the quality is good enough I'm sure the
> core developers will grant you SVN access. Development of Lazarus will
> go faster for you and the future of Lazarus will look shiny again.
> Please keep us informed of your progress.

It's only the poor AutoSize hack that prevents the use of other layout 
managers. Give it a well documented API, and let the users add their own 
layout managers as e.g. TChildSizing descendants, as everybody already 
can add an docking manager. *Then* you can ask the users to implement 
their own layout managers, while asking them to implement a layout 
manager *interface* is the *wrong* way.

The same for the designer interface, which should be specified *before* 
you can ask the user to implement it. A published LayoutManagerClass and 
a LayoutData property in the control/form properties is the minimal 
requirement for such an interface. In the easiest case no extra designer 
support is required at all, when a layout manager works like a docking 
manager, where the location of the dropped control is sufficient to 
determine its final origin and extent. Further fine-tuning can use the 
already existing ChildSizing interface, and an generalized AnchorDocking 
(LayoutCustomization) dialog, if necessary.

Conclusion: The LCL already contains all required features and hooks for 
layout managers, only in a too specialized implementation. Make it more 
general and open to user supplied players, and the layout manager 
discussion can be closed forever, leaving more time for other issues to 
the core developers :-)


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