Question

I want to create a custom control derived from TPanel that contains an image and a bunch of other controls on it.
After writing the code I have some weird behavior in my program. I realized that some vars that were supposed to be initialized in TDisplay.Resize (override) was never initialized because the Resize was never executed.

To ‘solve it’ I put a button on a form and called the LoadSample function which calls ClientHeight which calls Resize FOR THE FIRST TIME!

constructor TDisplay.Create(AOwner: TComponent);
begin
 inherited Create(AOwner);
 Ready         := FALSE;                                                       
 Parent        := Owner as TWinControl;
 Width         := 200;
 Height        := 86;                 
 Color         := clSilver;
 Caption       := '';
 DoubleBuffered:= TRUE;


  InternalDisplay:= TImage32.Create(Self);
  with Display DO
   begin
    Parent        := Self;
    Bitmap.Width  := 1;                                                        
    Bitmap.Height := 1;
    RepaintMode   := rmOptimizer;     
    Align         := alClient;
    SetupBitmap(TRUE, clBlack32);    
    Visible       := TRUE;
    OnMouseDown   := DMouseDown;
   end;
 ...
end;

Update:
Also the InternalDisplay won’t be aligned to its parent size until I manually resize the form (the control) at runtime. Only then it will act as it was supposed to act (to stay aligned to alClient).

Update 2:
Resize is declared like that: procedure Resize; override;

Update 3:
I removed the ClientHeight line from my construnctor and move it here:

procedure TDisplay.LoadSample(VAR Obj: TMySample; CONST bReleaseOnExit: boolean)
begin
 ClientHeight;  <--------- this will call Resize for the first time and my code will be finally initialized. But until this point my display will look odd because the code was never initialized. So the user will see weird stuff until it pushes the 'LoadSample' button.
 more code here....
end;

Update 4:
I used HandleNeeded as David suggested and it solved the initialization problem. However, the Image still won’t align to the entire client area unless I manually resize the form/control.

Update 5
Continued here, as David suggested: TImage won't align to parent

Answer 1

Your form isn’t showing yet, so it isn’t yet able to receive Windows messages (such as the resize message that triggers the OnResize event).