WindowPos access violation (message LM_WINDOWPOSCHANGED)

[elioenaishalom]

Please,
if you can help, thanks in advance.
I tried to control the MainForm position (top and left) through the procedure bellow.
Problem is : If the form move a pixel the app return Access violation, what am I doing wrong ?

Code: [Select]

{procedure WindowPosChanged(var Msg: TLMessage); message LM_WINDOWPOSCHANGED;}
procedure TMainForm.WindowPosChanged(var Msg: TLMessage);
var
  vx, vy: integer;
  P: ^WindowPos;
begin
  P := Pointer(Msg.LParam);
  Vx := P^.x;
  Vy := P^.y;
  StatusBar1.Panels[0].Text := IntToStr(Vx);
  StatusBar1.Panels[1].Text := IntToStr(Vy);
end;(Lazarus 1.0.6 - Windows7)

[taazz]

Try to use the existing mechanisms as much as possible this way you are going to be fairly sure that the code will be supported in most /all platforms LCL can go so do something along the lines of

{procedure WindowPosChanged(var Msg: TLMWindowPosChanged); message LM_WINDOWPOSCHANGED;}
procedure TMainForm.WindowPosChanged(var Msg: TLMWindowPosChanged);
var
  vx, vy: integer;
begin
  Vx := Msg.WindowPos^.x;
  Vy := Msg.WindowPos^.y;
  StatusBar1.Panels[0].Text := IntToStr(Vx);
  StatusBar1.Panels[1].Text := IntToStr(Vy);
end;

That should work.

[elioenaishalom]

Thanks for reply but I changed code and not worked (same error).

[engkin]

Code: [Select]

procedure TMainForm.WindowPosChanged(var Msg: TLMessage);
var
  vx, vy: integer;
  P: ^WindowPos;
begin
  P := Pointer(Msg.LParam);

  if not assigned(p) then exit;

  Vx := P^.x;
  Vy := P^.y;
  StatusBar1.Panels[0].Text := IntToStr(Vx);
  StatusBar1.Panels[1].Text := IntToStr(Vy);
end;

Edit:
It comes from:

Code: [Select]

procedure TWinControl.SendMoveSizeMessages(SizeChanged, PosChanged: boolean);
..
  Perform(LM_WindowposChanged, 0, 0);


[elioenaishalom]

Works !!!

thanks very much.