Dear Dennis,
I read the help of Delphi, it says :
A protected member is visible anywhere in the module where its class is
declared
and from any descendant class, regardless of the module where the descendant
class appears.
Now I purposely make my constructor to be Protected member, then step into
myPic.Graphic := nGra;
in the unit of graphics.pas,
the call
NewGraphic := TGraphicClass(Value.ClassType).Create;
of Tpicture class still call my protected construstor correctly.
But nGra := gCls.Create won't. Why?
//----------------------------------------
Type TMyGraphic = class(TGraphic)
Protected
constructor Create; override;
public
procedure Assign(Source: TPersistent); override;
end;
procedure TMyGraphic.Assign(Source: TPersistent);
begin
//
end;
constructor TMyGraphic.Create;
begin
inherited;
CallNo := CallNo + 1;
end;
var CallNo : Integer;
//------------------------------------------------------------------------
procedure TryIt;
var gCls : TGraphicClass;
nGra : TGraphic;
myPic : TPicture;
begin
CallNo := 0;
gCls := TGraphicClass(TMyGraphic);
nGra := gCls.Create;
ShowMessage(IntToStr(CallNo)); // 0
myPic := TPicture.Create;
myPic.Graphic := nGra;
ShowMessage(IntToStr(CallNo)); // 1
end;
-----Original Message-----
From: Jianming Lin (ASL) [mailto:JianmingL@;aslnz.co.nz]
Sent: Friday, 18 October 2002 11:20 a.m.
To: Multiple recipients of list delphi
Subject: RE: [DUG]: polymorphism problem
Dear Dennis,
YOU are right, TGraphic's constructor in D5 IS INDEED protected.
Thanks everyone who has replied to this thread
Jianming
-----Original Message-----
From: Dennis Chuah [mailto:dennis_cs_chuah@;hotmail.com]
Sent: Friday, 18 October 2002 11:02 a.m.
To: Multiple recipients of list delphi
Subject: Re: [DUG]: polymorphism problem
I stepped through your code in D6 (don't have D5 installed on this
machine) - but perhaps there is something wrong in D5? I am wondering in D5
whether TGraphic's constructor is protected?
Dennis.
----- Original Message -----
From: "Jianming Lin (ASL)" <[EMAIL PROTECTED]>
To: "Multiple recipients of list delphi" <[EMAIL PROTECTED]>
Sent: Friday, October 18, 2002 9:10 AM
Subject: RE: [DUG]: polymorphism problem
>
>
> -----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.
>
> Checked
>
> 2. What if you replaced your code with:
> NGraphic := TMetadata.Create;
>
> Step through the code - does it call TMetadata.Create?
>
> Yes it does
>
> 3. Check the class type of NGraphic and compare
Pointer(NGraphic.ClassType)
> against Pointer(TMetadata). Are they the same pointer values?
>
> Checked. still not get called.
>
> What version of Delphi are you using?
>
> D5 Ent
>
>
> 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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