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Date Posted: 17:44:06 05/04/01 Fri
Author: Michel
Subject: Re: Problem in using TGraphicClass
In reply to: Wen 's message, "Re: Problem in using TGraphicClass" on 21:32:06 05/03/01 Thu


Hi Wen,

It does look like a Delphi problem. The constructor of TGraphic is virtual, so in principle, using GraphicClass.Create should work. Strange...

Best regards,

Michel

>Yes, if I just modify the declaration of GraphicClass
>from TGraphicClass to TDibGraphicClass and keep all
>else intack. The code will work correctly. Moreover,
>as I have said, GraphicClass.Create will not bring me
>to the create method
>of TJpegGraphic, nor TDibGraphic, even nor TGraphic!!!.
>This may be a bug in Delphi. However, TPicture with
>registration of TJpegGraphic will work all right.
>Although
>it also uses TGraphicClass as its class reference!
>
>
>>
>>Hi Wen,
>>
>>The structure of the code looks fine. The first thing
>>I would try is replacing the types TGraphicClass and
>>TGraphic with TDibGraphicClass and TDibGraphic
>>respectively.
>>
>>I wonder if Delphi is not confused with the run-time
>>type information when handling class variables. If you
>>trace into GraphicClass.Create, does the debugger
>>bring you to an Envision unit?
>>
>>Best regards,
>>
>>Michel
>>
>>
>>
>>
>>
>>>I use TJpegGraphic as following:
>>>var
>>> GraphicClass: TGraphicClass;
>>> Graphic: TGraphic:
>>>begin
>>> GraphicClass := TJpegGraphic;
>>> Graphic := GraphicClass.Create;
>>> Graphic.LoadFromFile('mypicture.jpg');
>>>//Access Violation every time I execute here
>>>end;
>>>In addition, I found in the second statement
>>>GraphicClass.Create does not call the
>>>
>>>TJpegGraphic.Create method.
>>>
>>>However, if modified the above code to:
>>>begin
>>> Graphic := TJpegGraphic.Create;
>>> Graphic.LoadFromFile('mypicture.abc');
>>>end;
>>>
>>>all work correctly, Can anyone tell me what wrong
>with
>>>the first code sippet.

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