Question

I want to be able to limit where a component is created.

Like for instance, TMyChild could be a TButton, and TMyParent could be a TPanel,
and when I drop MyChild onto some other component I want MyChild to check if
it is being created in a TMyParent/TPanel or not.

If it is, then fine lets do it, if it is NOT created in a TMyParent/TPanel then cancel
the TMyChild creation and show a message that says something like: “Sorry, MyChild needs to be created in MyParent!”.

Thank you!

Answer 1

You must override the Controls.TControl.SetParent method.

  TMyChild = class(TControl)
  protected
    procedure SetParent(AParent: TWinControl); override;
  end;


procedure TMyChild.SetParent(AParent: TWinControl);
begin
  if (AParent <> nil) then
  begin
    if not (AParent is TMyParent) then
      raise Exception.CreateFmt('Sorry, MyChild needs to be created in MyParent!', [ClassName]);
  end;
  inherited;
end;