MVC Lazarus Wrong number of parameters

Question

I'm trying to implement MVC pattern in lazarus, I've created the model and the view (directly from the designer). Now, I'm writing the "controller", but when I try to re-assign the auto-generated method "Button.OnClick", I've a compilation error :

controller.pas(31,44) Error: Wrong number of parameters specified for call to "QuitBtn"

The constructor of the controller :

constructor TController.Create(AModel : TGame ; AView : TFArena);
begin
  Model := AModel;
  FView := AView;

  {Compilation Error}
  FView.Quit.OnClick := TController.QuitBtn;
end;

And the procedure :

procedure TController.QuitBtn(Sender : TObject);
begin
  ShowMessage('MVC READY');
end;

Method auto-generated from lazarus

procedure TFArena.QuitClick(Sender: TObject);
begin
  {Nothing because she's gonna be over assigned}
end;

So, the both avec the same parameter "Sender : TObject"

Thanks for reading

David Heffernan · Accepted Answer · 2013-09-19T19:30:27.867

3

The OnClick event must be implemented a method of an instance. You've passed the code part of the method, but are missing the data, the instance.

You must get hold of an instance of TController. Now, you have one of those at hand since your code runs in the constructor of TController. So just write it like this:

FView.Quit.OnClick := Self.QuitBtn;

Of course, you can always omit Self which is idiomatic.

FView.Quit.OnClick := QuitBtn;

I'm also not sure that QuitBtn is a great name for an event handler. It sounds more like the name of a UI widget.

And perhaps you are using a compiler mode that requires the @ operator to generate method references:

FView.Quit.OnClick := @QuitBtn;

edited Sep 19 '13 at 19:30

answered Sep 19 '13 at 19:04

David Heffernan

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Thanks for answer, I try the 2 part of code, but, the same error – Titouan56 Sep 19 '13 at 19:15
1

You quite sure of that? Would work in Delphi. Are you in different mode? Perhaps an @ is needed. – David Heffernan Sep 19 '13 at 19:22
it Works with @, thanks, I haven't thought to a low-level implementation (Throught is it implicit), Thanks ! PS : If you could edit your answer for the other :) – Titouan56 Sep 19 '13 at 19:29
So, which compiler mode are you using anyway? – David Heffernan Sep 19 '13 at 19:31
default mode when you create a new project with Lazarus – Titouan56 Sep 19 '13 at 19:33
That's objfpc, not Delphi, and objfpc indeed needs an @. It makes some cases less ambiguous. – Marco van de Voort Sep 24 '13 at 11:28
@marco Does that mode retain type safety for procedural variables. Bug bear of mine with delphi is the default untyped @ operator – David Heffernan Sep 24 '13 at 11:30
This @ isn't the normal @. Yes, it will on the full prototype, including calling convention. (and error on mismatch, not hint). – Marco van de Voort Sep 24 '13 at 11:38

MVC Lazarus Wrong number of parameters

1 Answers1