Setting graphic at design-time

[bobbie100]

I need to select a bitmap image in a descendant of TGraphicControl to be displayed at design-time. TImage does this, but I don't want to use TImage (variety of reasons). I have Published the TBitmap as foolows:

type
MyGraphicControl = class(TGraphicControl)
private
FBaseBitmap: TBitmap;
...
protected
procedure SetBaseBitmap(ABitmap: TBitmap);
...
published
property BaseBitmap: TBitmap read FBaseBitmap write SetBaseBitmap;
...
end;
implementation
...
procedure MyGraphicControl.SetBaseBitmap(ABitmap: TBitmap);
begin
????????
end;

Problem is that whatever I seem to try at ?????? I get an access violation error when I select a .bmp file in the Object Inspector at design-time (using the standard graphic property editor).

Also, how do I get the bitmap displayed at design-time? Is it as simple as using
Canvas.Draw(0,0,FBaseBitmap);
in SetBaseBitmap?

Any suggestions (not too rude) would be much appreciated.

 

[bobbie100]

Sorry for bothering anyone who looked at this. I suddenly realised that I have the TImage source listing. The following test component did what I wanted, so I'll base my implementation in the application on this. However, any comments would be gratefully received.
[tt]
unit MyGraphicControl;

interface

uses
SysUtils, Classes, Controls, Graphics;

type
TMyGraphicControl = class(TGraphicControl)
private
FBaseBitmap: TBitmap;
protected
procedure SetBaseBitmap(Value: TBitmap);
procedure BaseBitmapChanged(Sender: TObject);
procedure Paint; override;
published
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
property BaseBitmap: TBitmap read FBaseBitmap write SetBaseBitmap;
end;

procedure Register;

implementation

procedure Register;
begin
RegisterComponents('My Components', [TMyGraphicControl]);
end;

constructor TMyGraphicControl.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
{ Parent set here to support setting Transparent in BaseBitmapChanged }
Parent := AOwner as TWinControl;
FBaseBitmap := TBitmap.Create;
FBaseBitmap.OnChange := BaseBitmapChanged;
end;

destructor TMyGraphicControl.Destroy;
begin
FBaseBitmap.Free;
inherited Destroy;
end;

procedure TMyGraphicControl.BaseBitmapChanged(Sender: TObject);
begin
if csDesigning in ComponentState then
begin
inherited Canvas.Brush.Style := bsClear;
inherited Canvas.FillRect(Rect(0, 0, Width, Height));
if FBaseBitmap.Width > 0 and FBaseBitmap.Height then
begin
Width := FBaseBitmap.Width;
Height := FBaseBitmap.Height;
FBaseBitmap.Transparent := True; //Fixed setting for test purposes only
inherited Canvas.Draw(0, 0, FBaseBitmap);
end;
end;
end;

procedure TMyGraphicControl.Paint;
begin
BaseBitmapChanged(Self);
end;

procedure TMyGraphicControl.SetBaseBitmap(Value: TBitmap);
begin
FBaseBitmap.Assign(Value);
end;

end.[/tt]

 

[BillDoorNZ]

one suggestion.....in BaseBitmapChanged there is an if statement that reads:

if FBaseBitmap.Width > 0 and FBaseBitmap.Height then

I would change it to be a little more readable

if (FBaseBitmap.Width > 0) and (FBaseBitmap.Height > 0) then

 

[bobbie100]

Well done BillNZ for spotting the deliberate cock-up. Your suggestion is what I meant to write.....Really!!! Looking at the code I'm amazed it worked. My only excuse is that this is gash code for testing, but many thanks for looking.