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Points for ptmcomp: Why setClassLong isn't working

Posted on 2000-05-06
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Last Modified: 2012-06-27
Hi, ptmComp. Please post the same answer you gave to my othe question and I'll give you the points.

In Delphi 5 I'm using setClassLong to replace the window class background brush but it's not working. I tried with a solid brush and a bitmap brush.

var
brushBackGround : HBrush;
bm:graphics.tbitmap;
begin
bm := graphics.TBitmap.create;
try
bm.loadFromFile('patron1.bmp');
// brushBackGround := createPatternBrush(bm.handle);
brushBackGround := createSolidBrush(clRed);
setClassLong(application.handle,GCL_HBrBackGround,brushBackGround);
try
Application.Initialize;
Application.CreateForm(TForm1, Form1); // form1 is an empty form
// setClassLong(form1.handle,GCL_HBrBackGround,brushBackGround); tried this, didn't work neither
Application.Run;
finally
deleteObject(brushBackGround);
end;
finally
bm.Free;
end;
end.

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Question by:ms99
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1 Comment
 
LVL 10

Accepted Solution

by:
ptmcomp earned 25 total points
ID: 2785599
The problem is that Delphi overrides the WM_ERASEBKGND message handler.

procedure TWinControl.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  { Only erase background if we're not doublebuffering or painting to memory. }
  if not FDoubleBuffered or
    (TMessage(Message).wParam = TMessage(Message).lParam) then
    FillRect(Message.DC, ClientRect, FBrush.Handle); // here Delpi uses FBrush.Handle instead of the window class brush
  Message.Result := 1; // message handled
end;

If you want to change to color of your window class, change the color property in the constructor.

But this works:

procedure TForm1.FormCreate(Sender: TObject);
begin
  Form1.Brush.Bitmap:= TBitmap.Create;
  Form1.Brush.Bitmap.LoadFromFile('c:\winnt\Santa Fe-Stuck.bmp');
end;

Regards, ptm.
0

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