On Mon, 21 Aug 2006 19:52:34 +0000
Albert Zeyer <[EMAIL PROTECTED]> wrote:
> Am Montag, den 21.08.2006, 19:17 +0200 schrieb Mattias Gaertner:
>
> > On Mon, 21 Aug 2006 14:30:06 +0000
> > Albert Zeyer <[EMAIL PROTECTED]> wrote:
> > > > With TPersistent it would work like this
> > > > TMyBase = class(TPersistent)
> > > > public
> > > > function CreateCopy: TMyBase;
> > > > procedure Assign(Source: TPersistent); override;
> > > > end;
> > > >
> > > > it would be
> > > > function TMyBase.CreateCopy: TMyBase;
> > > > begin
> > > > Result := TMyBaseClass(Self.ClassType).Create;
> > > > Result.Assign(Self);
> > > > end;
> > > >
> > > > Every class must override the Assign method to copy all added
> > > > values.
> > > >
> > >
> > > But in this case, it would also not call the constructor of my
> > > inherited classes.
> >
> > Why not? Did you test it?
>
>
> Yes, I tested the following code:
>
> // ------------------------------------
> ...
> type
> TBaseTestObject = class(TPersistent)
> constructor Create();
> procedure DoSomething(); virtual; abstract;
> end;
>
> TBaseTestClass = class of TBaseTestObject;
>
> TTestObject = class(TBaseTestObject)
> public
> constructor Create();
> destructor Destroy(); override;
> procedure DoSomething(); override;
> end;
>
> TSkriptTestForm = class(TForm)
> Button1: TButton;
> procedure Button1Click(Sender: TObject);
> mTest: TTestObject;
> end;
>
> var
> SkriptTestForm: TSkriptTestForm;
>
> implementation
>
> procedure TSkriptTestForm.Button1Click(Sender: TObject);
> var
> cls: TBaseTestClass;
> begin
> cls := TTestObject;
> mTest := cls.Create() as TTestObject;
> mTest.DoSomething();
> end;
>
> constructor TBaseTestObject.Create();
> begin
> inherited Create();
> WriteLn('TBaseTestObject Create');
> end;
>
> constructor TTestObject.Create();
> begin
> inherited Create();
> WriteLn('TTestObject Create');
> end;
>
> destructor TTestObject.Destroy();
> begin
> WriteLn('TTestObject Destroy');
> inherited Destroy();
> end;
>
> procedure TTestObject.DoSomething();
> begin
> WriteLn('TTestObject DoSomething');
> end;
>
> // ------------------------------------
>
> TTestObject.Create won't ever be called (only TBaseTestObject.Create
> will be, but if I use TClass instead of TBaseTestClass, it also won't
> be). It also makes no difference if I use TPersistent as base or
> simply TObject. But the DoSomething call works nevertheless,
> therefore it seems, that the VMT (and other stuff) is initialized
> correctly, but my own constructor won't ever be called.
Make 'Create' virtual.
Mattias
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