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Overriding Private methods

Posted on 1997-12-15
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Last Modified: 2010-04-04
I have to override a private method :

TTrackBar
Priate
  procedure SetPosition(Value: Integer) of TTrackBar

How ?
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Question by:Matvey
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3 Comments
 
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Accepted Solution

by:
julio011597 earned 0 total points
ID: 1353696
You cannot override a private method.
To override a method, the method must be, at least, protected (so that your inherited component can see it), and virtual (so that it may be overriden).

Anyway you can _hide_ it, i.e. redeclare it in your inherited component.
Consider, anyway, that you'll lose the chance to call the inherited method by the 'inherited' keyword.

HTH, julio
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Expert Comment

by:ra_tim
ID: 1353697
Maybe it is possible to hack in the RTTI, the Delphi Runtime information.

To access a local variable is simple:

// TClass1 contains a private variable
TClass1 = class
  private
    FSecret : integer;
end;

// TClass2 is a has the same structure (and byte organisation)
// as TClass1 only that members are public.

TClass2 = class
  public
     FSecret : integer;
end;

procedure Hack;
var a : TClass1;
begin
  a := TClass1.Create;
  TClass2(a).FSecret := 100;
  // This cast makes it possible to access a private variable
end;


 
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LVL 3

Author Comment

by:Matvey
ID: 1353698
Thank you ra_tim, but what I need is to add some code to a private method after I call the Inherited method (or get the method do whatever it has to do any other way).
But anyway, I can copy the source code of that private method, rewrite it in my control and do the thing you say.
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