Message CM_ShowingChanged arrives not always?

[AlexTP]

Here is demo project. Attached.
When I click all 3 buttons, my TCustomControl shows/hides. And Listbox1 log must show that my control got the CM_SHOWINGCHANGED. It shows it only on the 1st showing of control. I expected that event is got on every toggling, ie also when I click buttons many times: 1 2 3 1 2 3 1 2 3 etc.

It's on all widgetsets: win64 gtk2 qt5 qt6.

How TCustomControl can get the event of parent's showing/hiding?

[LeP]

It's simple: My1, My2, My3 changed only 1 time. After that they don't change anymore ... parents change but not My1, etc ... They stay always showed (but not visible 'cause parents).

Try insert where Panel1.Hide and Show are  My1 too.

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. begin
3.   Panel1.Show;
4.   My1.Show;
5.   Panel2.Hide;
6.   Panel3.Hide;
7. end;
8.  
9. procedure TForm1.Button2Click(Sender: TObject);
10. begin
11.   Panel1.Hide;
12.   My1.Hide;
13.   Panel2.Show;
14.   Panel3.Hide;
15. end;
16.  
17. procedure TForm1.Button3Click(Sender: TObject);
18. begin
19.   Panel1.Hide;
20.   My1.Hide;
21.   Panel2.Hide;
22.   Panel3.Show;
23. end;
24.  

[LeP]

How TCustomControl can get the event of parent's showing/hiding?

In Delphi you must change your procedure, intercept this message:

Code: Pascal  [Select][+][-]

1.   TMy = class(TPanel)
2.   protected
3.     procedure CMParentVisibleChanged(var Message: TMessage); message CM_PARENTVISIBLECHANGED;
4.   end;
5.  

But in Lazarus that message non exists ... 

[jamie]

Here is demo project. Attached.
When I click all 3 buttons, my TCustomControl shows/hides. And Listbox1 log must show that my control got the CM_SHOWINGCHANGED. It shows it only on the 1st showing of control. I expected that event is got on every toggling, ie also when I click buttons many times: 1 2 3 1 2 3 1 2 3 etc.

It's on all widgetsets: win64 gtk2 qt5 qt6.

How TCustomControl can get the event of parent's showing/hiding?

 You could process the "LM_SHOWWINDOW" message. That can report if the parent is changing etc.

Jamie

[LeP]

You could process the "LM_SHOWWINDOW" message. That can report if the parent is changing etc.
Jamie

I tried with LM_SHOWWINDOW but it's never sended to child (even if its visibility changes).

[jamie]

You could process the "LM_SHOWWINDOW" message. That can report if the parent is changing etc.
Jamie

I tried with LM_SHOWWINDOW but it's never sended to child (even if its visibility changes).

Did you override the WndPrc to do that?

I know many messags are blocked in the LCL but lots of them get through using the WndProc

Jamie

[LeP]

You could process the "LM_SHOWWINDOW" message. That can report if the parent is changing etc.
Jamie

I tried with LM_SHOWWINDOW but it's never sended to child (even if its visibility changes).

Did you override the WndPrc to do that?
I know many messags are blocked in the LCL but lots of them get through using the WndProc
Jamie

I tried, and the only time that message is sent is when I close the application (also tested with the debugger).

[AlexTP]

Lazarus was improved today (Git main). Now CM_ShowingChanged works like in Delphi. Thanks to Zeljko.