Hoping somebody may be able to explain why the following doesn't stop the Form closing.

Button1 sets the method pointer correctly (I believe), as when closing the form the showmessage occurs as expected (and shows the correct form name).
But the form closes anyway.

procedure MyFormCloseQuery(Sender: TObject; var CanClose: boolean);
begin
   ShowMessage('MyCloseQuery:'+TControl(Sender).Name);
   CanClose := FALSE;
end;
procedure TformMain.Button1Click(Sender: TObject);
var
   OnCloseQueryMethod            :TCloseQueryEvent;
begin
   TMethod(OnCloseQueryMethod).Code := @MyFormCloseQuery;
   TMethod(OnCloseQueryMethod).Data := formMain;
   TForm(formMain).OnCloseQuery     := OnCloseQueryMethod;
end;

Thanks - SteveG

Methods have a hidden Self parameter:

procedure MyFormCloseQuery(Self: TObject; Sender: TObject; var
CanClose: boolean);

Keep in mind that this is an implementation detail of the compiler, which may be different on other platforms, may not work with special compiler flags and may change in future.

Mattias

Here formMain.OnCloseQuery := @MyFormCloseQuery should be sufficient, unless the OnCloseQuery handler deals with data in the form. But in this case the handler should be made part of the formMain code, so that it can access the form's fields and methods.

When your formMain closes anyway, I'd suggest to write an OnClose handler and set CloseAction to caNone there.

AFAIR OnCloseQuery is intended for ending an application, where the application denies ending when any form reports CanClose=False. Closing individual forms instead should be handled in OnClose.

DoDi

Ah, I missed *that* essential detail in my answer :-(

Thanks
DoDi

[...] Here formMain.OnCloseQuery := @MyFormCloseQuery should be sufficient,

Compiler will refuse that.

OnCloseQuery defines if to close or not, OnClose defines how to close.

Mattias

would there be any way to accomplish what I'm after then ? I am trying to indirectly prevent the form closing (by passing the Form to a Method / Proc)
So with no additions to the original forms class or instance.

Thanks

You can add your handler to the form containing Button1. Then the handler is a method, ready for assignment to the OnFormClose of any form in your project.

DoDi

Thanks Hans, will try that out

Steve