TGraphicClass is defined in Graphics.pas as :
TGraphicClass = class of TGraphic;
Anothe bizarre problem is:
procedure TryId;
var gCls : TGraphicClass;
nGra : TGraphic;
myPic : TPicture;
begin
gCls := TGraphicClass(TMetafile);
nGra := gCls.Create;
myPic := TPicture.Create;
myPic.Graphic := nGra;
end;
Press F7, trace into gCls.Create, TMetaFile constructor is not called.
While I trace into myPic.Graphic, it goes into:
TPicture.SetGraphic(Value: TGraphic);
...
NewGraphic := TGraphicClass(Value.ClassType).Create;
then TMetafile constructor is called correctly.
So my environment setting is not wrong.
But why gCls.Create won't call TMetafile constructor?
-----Original Message-----
From: Chris Reynolds [mailto:chrisr@;instantObjects.com]
Sent: Friday, 18 October 2002 9:27 a.m.
To: Multiple recipients of list delphi
Subject: Re: RE: [DUG]: polymorphism problem
Only just focussed on this thread after deleting several previous.
Maybe I missed that message but how is TGraphicClass?
>More Examples of my problem:
>
>//------------------------------------------------------------------------
>Type TMyGraphic = class(TGraphic)
> public
> constructor Create; override;
> end;
>
>
>constructor TMyGraphic.Create;
>begin
> inherited;
> ShowMessage('kk');
>end;
>
>//------------------------------------------------------------------------
>
>procedure TryIt;
>var gCls : TGraphicClass;
> nGra : TGraphic;
>begin
> gCls := TGraphicClass(TMyGraphic);
> nGra := gcls.Create; // TMyGraphic costructor won't
be
>called, Why?
> nGra := TMyGraphic.Create; // called successfully
>end;
>
>
>
>
>
>
>-----Original Message-----
>From: Dennis Chuah [mailto:dennis_cs_chuah@;hotmail.com]
>Sent: Friday, 18 October 2002 7:14 a.m.
>To: Multiple recipients of list delphi
>Subject: Re: [DUG]: polymorphism problem
>
>
>
>I stepped through your code and it *DEFINITELY* calls TMetadata.Create.
>What you have done looks correct and this is certainly not a polymorphism
>pproblem. Few suggestions:
>
>1. Check that you do not have $(DELPHI)\Lib in your project path - it
>should only be in the global library path.
>2. What if you replaced your code with:
> NGraphic := TMetadata.Create;
>
>Step through the code - does it call TMetadata.Create?
>
>3. Check the class type of NGraphic and compare
Pointer(NGraphic.ClassType)
>against Pointer(TMetadata). Are they the same pointer values?
>
>What version of Delphi are you using?
>
>Dennis.
>
>----- Original Message -----
>From: Jianming Lin (ASL)
>To: Multiple recipients of list delphi
>Sent: Thursday, October 17, 2002 4:35 PM
>Subject: [DUG]: polymorphism problem
>
>
>
>
>G'Day, guys,
>
>procedure TryMetadata(ImgType : Integer);
>var NGraphic: TGraphic;
> GraphicClass: TGraphicClass;
>begin
> ImgType := 1;
> case ImgType of
> 1 : GraphicClass := TMetaFile;
> 2 : GraphicClass := TBitmap;
> end;
> NGraphic := GraphicClass.Create;
>end;
>
>
>Why constructor of TMetafile.Create is not called instead only
>TObject.Create is called?
>
>
>
>
>
>[Jianming Lin (ASL)]
>
>
>
>
>
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