Replacing a component class in delphi

by

In your form you can override the ReadState method like so:

type
  TMyForm = class(TForm)
  protected
    procedure ReadState(Reader: TReader); override;
  end;

procedure TMyForm.ReadState(Reader: TReader);
begin
  Reader.OnFindComponentClass := FindComponentClass;
  inherited;
end;

procedure TMyForm.FindComponentClass(Reader: TReader; const ClassName: string;
  var ComponentClass: TComponentClass);
begin
  if ComponentClass=TButton then begin
    ComponentClass := TMySuperDuperButton;
  end else if ComponentClass=TEdit then begin
    ComponentClass := TMyTotallyAwesomeEdit;
  end;
end;

There are likely numerous other ways to do this, but this is how I do it!

EDIT: Inspecting TReader.GetFieldClass(Instance: TObject; const ClassName: string) suggests the hack that Mason recalls. The first line sets ClassType := Instance.ClassType. So I suspect that by changing the declaration in the pas file from Button1: TButton to Button1: MyUnit.TButton will result in your button being created. Or perhaps the hack was to add MyUnit to the uses clause right at the end so that your version of TButton is the one that is in scope. However, none of this sounds very practical.

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