The implementation of the TTabControl seems to cause headaches, and
reveals wrong assumptions of the devlopers about the behaviour of that
control :-(
When I recently submitted an patch, with a new implementation of the
TTabControl (named TTabs in the patch), this implementation was tested
with the Win32 widgetset, and was fully compatible with the Delphi
TTabControl - in contrast to any preceding implementation.
Felipe acted a bit too fast, and replaced the TTabControl by the new
implementation, without waiting for the complete implementation with all
widgetsets. The consequential problems showed up very soon :-(
When consequently problems with other widgetsets occured, he removed the
intented implementation of TTabs (TNewTabControl), making it unusable at
all. This step was undone later.
When it turned out that the IDEInspector uses a TTabControl, and stopped
working (#19803) due to an misplaced override of ChildClassAllowed, this
problem was not fixed in the suggested and obvious way (by moving that
method into TPageControl). Instead the wrong assumption was stated, that
a TTabControl cannot have child controls - what is not true for a Delphi
compatible control.
So where are we now? We are back to the old TTabControl, that is not
Delphi compatible, and have a TNewTabControl without an designer. Was
this worth all the trouble?
IMO we should accept that a Delphi compatible TTabControl doesn't exist
yet, for widgetsets other than Win32. What can/should we do, when it
turns out that such a control can not be implemented in all widgetsets?
Why not offer the new implementation (TTabs/TNewTabControl) as
TTabControl, to make Delphi migrants happy, and restrict its use to only
the supported widgetsets? At the same time the old implementation can be
renamed into TLazTabControl, that is not fully Delphi compatible, but
immediately usable with all widgetsets?
And since the old TTabControl and TNotebook effectively share the same
code, except for the control that shows the tabs, it would be a good
idea to merge both into a common base class. The difference between both
controls is implemented in their Pages classes (TUNBPages,
TTabControlNoteBookStrings), so that effectivly only their constructors
have to be different, where this object is created. An even simpler
solution were to make the tabs switchable ON/OFF.
More things can be simplified, in detail the difference between visible
and invisible pages, which applies *only* to the TPageControl. By moving
that part out of the widgetsets into TPageControl, the implementation of
the widgetsets and all TCustomTabControl descendants could be simplified
a lot. Then also the restrictions would become more obvious, introduced
by the various widgetsets.
DoDi
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