using System.Drawing.Graphics.FromHdc() in combobox draw item

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5 total messages Started by Horst Reichert Thu, 28 Dec 2006 10:22

#212

Author: Horst Reichert
Date: Thu, 28 Dec 2006 10:22

22 lines
1755 bytes

I want to apply special drawing routines using System.Drawing.Graphics 
inside a combo box user drawing routine.

procedure TRtDashStylesCombo.DrawItem(Index: Integer; Rect:TRect; 
State:TOwnerDrawState);
var Gap: Single; dGr: System.Drawing.Graphics; dPen: System.Drawing.Pen;
begin
  Canvas.Brush.Color := Color;
  Canvas.FillRect(Rect);
  Gap := ItemHeight*0.5;
  dGr := System.Drawing.Graphics.FromHdc(IntPtr(Canvas.Handle));
  dPen := 
System.Drawing.Pen.Create(System.Drawing.Color.FromArgb(FLineColor));
....

The code woks as expected during firstly drawing the control and dropping 
down items. But sometimes especially after clicking other combos and re 
entering the user drawn combo it will run into a arithmetic overflow error 
caused by the FromHdc creation of the graphics object.
Any idea how to solve this issue?

Regards Horst

Re: using System.Drawing.Graphics.FromHdc() in combobox draw item

#213

Author: Marc Rohloff TeamB
Date: Fri, 29 Dec 2006 00:02

15 lines
1781 bytes

On Thu, 28 Dec 2006 11:22:32 +0100, Horst Reichert wrote:

> The code woks as expected during firstly drawing the control and dropping 
> down items. But sometimes especially after clicking other combos and re 
> entering the user drawn combo it will run into a arithmetic overflow error 
> caused by the FromHdc creation of the graphics object.
> Any idea how to solve this issue?

Are you freeing or disposing of the graphics object?

Just out of curious why don't you just use the Canvas API's?

-- 
Marc Rohloff [TeamB]
marc rohloff -at- myrealbox -dot- com

Re: using System.Drawing.Graphics.FromHdc() in combobox draw item

#214

Author: Horst Reichert
Date: Fri, 29 Dec 2006 07:58

13 lines
1452 bytes

> Are you freeing or disposing of the graphics object?
The Error occures while creating the object.
I freeandnil() the object on exit of the procedure.

> Just out of curious why don't you just use the Canvas API's?
I need special features like transparency, different dasstyles with 
linewidth > 1 etc.

btw. the same error is displayed creating graphic objects with canvas.handle 
of TBitmap.

Regards Horst

Re: using System.Drawing.Graphics.FromHdc() in combobox draw item

#215

Author: Marc Rohloff TeamB
Date: Fri, 29 Dec 2006 18:26

10 lines
1611 bytes

On Fri, 29 Dec 2006 08:58:42 +0100, Horst Reichert wrote:

> btw. the same error is displayed creating graphic objects with canvas.handle 
> of TBitmap.

It sounds like some GD objects are not being released properly.

-- 
Marc Rohloff [TeamB]
marc rohloff -at- myrealbox -dot- com

Re: using System.Drawing.Graphics.FromHdc() in combobox draw item

#216

Author: Horst Reichert
Date: Sat, 30 Dec 2006 13:22

7 lines
1339 bytes

Solved it:
changed
  dGr := System.Drawing.Graphics.FromHdc(IntPtr(Canvas.Handle));
to
  dGr := System.Drawing.Graphics.FromHdc(IntPtr(Integer(Canvas.Handle)));

no crashes anymore ;-))

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