[Lazarus] TCustomNotebook

[Hans-Peter Diettrich]

Please let's continue the discussion here, not in Mantis.

Obviously we differ very much in our concepts, so that we should either 
come to a consent, or leave everything as bad as is.

Felipe Monteiro de Carvalho schrieb:

> General concepts:
> 1> Avoid changing the current TPageControl as much as possible,
> because it is extensively used and changes here might cause a pletora
> of problems
> 2> I think it is no problem to introduce heavy changes to TTabControl
> because it is rarely used
> 3> Use exactly the same class hierarchy as Delphi:
> 
> TCustomNotebook (in Delphi called TCustomTabControl)
> --> TPageControl
> --> TTabControl

This hierarchy would require to make the widgetsets independent from 
specialized Pages (TCustomPage descendants), and this is just what I 
have in mind.

> Just because this hard distinction of a control with pages and one
> without makes sense in Windows it doesn't mean at all that it makes
> sense in all widgetsets. Plus, just 1 implementation is better then 2
> spread across various classes for the widgetset interfaces.

Do you know of any widgetset, whose tabbed control has an idea of 
related pages?

Now at your notes in Mantis #19575:

 >>>>>>>>>>>>>>>>>>>>>
 > IMO it's overkill to base the widget on a TCustomNotebook - the internal
 > representation of the page data is of no interest to the widgetset. A 
simpler
 > base control would serve the same purpose, and would allow to implement a
 > Delphi compatible TTabControl.

overkill is not a problem. The LCL can have more functionality then 
Delphi, what is a problem is having a component based on a wrong class 
hierarchy or having less functionality then Delphi.
<<<<<<<<<<<<<<<<<<<<

You address the wrong class hierarchy of TTabControl, I assume?
I fully agree that TTabControl should inherit from LCL TCustomNotebook.


 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Ummm, I'm not sure about this patch. Some issues:

1> TPagedNotebook is a bad choice for a name, TPagedTabControl is better.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Feel free to rename it as you like.


 >>>>>>>>>>>>>>>>>>>>>>>>
2> You started by modifying TCustomNotebook ... I would much prefer if 
you started by fixing TTabControl instead.
<<<<<<<<<<<<<<<<<<<<<<<

Since TTabControl has no Pages, some methods and properties have to 
become at least virtual in TCustomNotebook.

Unlike in Delphi, where Pages are introduced only in TPageControl, the 
LCL TCustomNotebook *and* the widgetsets currently do not work without 
pages. But as I proved they *can* work without an PageList :-)

 >>>>>>>>>>>>>>>>>>>>>>>>
3> Your entire description of the bug seams to be based on a wrong 
understanding of how TTabControl should work. Why are you putting a 
TPanel inside a TTabControl??? TTabControl can only contain ... tabs. It 
can never contain a Panel nor a Page, nor anything else.
<<<<<<<<<<<<<<<<<<<<<<<<<

You misunderstand the demo application. In contrast, why does a 
TPageControl put TabSheets into the tabbed widget???

The panels in the demo program only demonstrate that a TTabControl *can* 
have associated controls, *not* bound to TCustomPage derivates, and 
*not* bound to the TTabControl as their parent.


 >>>>>>>>>>>>>>>>>>>>
4> Why do you expect Tabs.Tabs.AddObject to work at all? You should not 
use this AFAIK, you should use TTabControl.Tabs.Add()

http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/delphivclwin32/ComCtrls_TTabControl_Tabs.html 
[^]
<<<<<<<<<<<<<<<<<<<<

Please look at the sample program in that webpage - it does exactly 
this: hold related components (here an dialog) in the Objects[] property 
of the TTabControl.Tabs. This does *not* work with the LCL TTabControl, 
and this was the reason for my bug report.

Delphi TPageControl *also* uses the Tabs.Objects[] to hold the visible 
pages, associated with the tabs.


 >>>>>>>>>>>>>>>>>>>
I took a deeper look at the problem now and I am even more sure that you 
are starting at the wrong side of it.

TCustomNotebook cannot handle a tab control without pages at the moment, 
the very first thing should be implementing that in all widgetsets. I 
see two solutions:

1> Modify TCustomNotebook in all widgetsets so that it can handle a tab 
control without pages, in this case we would have:

-> TCustomNotebook <-- This class has a WS implementation
---> TPageControl
---> TTabControl
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

This essentiall is what I already did. Not in all widgetsets, but it 
should be easy to fix according problems everywhere. When a TCustomPage 
parameter is used only for passing further parameters to the widgetset, 
e.g. Page.Caption for the tab title, a widgetset should never try to 
deal with such an invisible (dummy) page - no window placement...

I used "ANotebook is TPagedNotebook" in the determination, whether the 
TabCtrl has associated *visible* pages. You can suggest any other 
notebook or page property for that purpose :-)


 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2> Change our hierarchy to this:

TCustomTabControl <-- Without a WS implementation
--> TCustomNotebook <-- This class has a WS implementation
-----> TPageControl
--> TTabControl <-- This class will gain a WS implementation
<<<<<<<<<<<<<<<<<<<<<<<<

Since both paged and unpaged controls are based on the same widget, and 
have much functionality in common, I'd suggest instead:

TCustomTabControl   <-- With basic WS implementation
--> TCustomNotebook <-- With extended WS implementation
-----> TPageControl
--> TTabControl

Then the TWSNotebook class can inherit from TWSTabControl.

Or associate TWSNotebook directly with TPageControl, however you like.


 >>>>>>>>>>>>>>>>>>>>>>>>>>>
The Delphi design of having a base class with tabs and a derivated one 
with pages is stupid and very windows-centric ... we won't be able to 
fully replicate that.
<<<<<<<<<<<<<<<<<<<<<<<<<<<

Sorry, that' nonsense :-(

*Every* tabbed widget can live without associated pages, at least it can 
be shrunk to only show the tabs and nothing else. This is what the 
current TTabControl does: show only the tabs of the embedded 
TCustomNotebook. But why use an embedded control for that purpose, when 
the widget already can do all that itself?


 >>>>>>>>>>>>>>>>>>>>
The closest solution is option 2, with the difference that 
TCustomTabControl will not be usable alone, because it won't have a WS 
implementation.
<<<<<<<<<<<<<<<<<<<<

That's the crappy workaround, currently used in TTabControl :-(


 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Option 1 would require making public a lot of tab stuff into 
TPageControl and a lot of page stuff into TTabControl
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Please give at least one concrete example.

Didn't I prove that a separation of paged from unpaged tabbed 
controls/widgets is feasable with little efforts?

I have already moved the affected stuff from TCustomNotebook into 
TPagedNotebook, and you can move that stuff from TPagedNotebook into 
TPageControl, and remove TPagedNotebook entirely, if you like.

DoDi