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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