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Groups > comp.lang.c++ > #87072

Re: calling a Event Handler within a class

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On 10/18/2022 10:06 AM, Jens wrote:
> Now, the question is: is it possible, to set a event handler on
> the OnClick event of a TButton object without having implicit a
> TObject inherited class ?
> 
> If the answer YES, then: How can this be done in C++ Builder ?
> 
> Under Delphi, I just assign it like:
> 
> ....
> btn := TButton.Create(AOwner);
> btn.Parent  := AOwner;
> btn.OnClick := btnOnClick;
> ....
> 
> In C++ Builder 6.0, i try the similar same procedure, but I fail
> with the code:
> 
> extern "C"
> __declspec(dllexport) void
> __stdcall foo(int owner)
> {
> ....
>    TForm *form = new TForm((HWND)owner);
> ....
>    TButton *btn = new TButton(form);
>    btn->Parent  = form;
>    btn->OnClick = btnOnClick;  // <-- this fails
> ....
> }

I am not that familiar with Borland products, but from a C++ perspective 
it would help if you could post the exact and complete error message - 
this might show which are the types of the OnClick member, and of 
btnOnClick.

You may also want to compare the following:

- declaration of the OnClick member of TButton - I guess this should be 
documented by Borland - it may be an object of some class that overloads 
the assignment operator; inspecting what is the expected argument type 
of such operator might help
- prototype of btnOnClick

In C++ an "event" is not a built-in primitive. C++ offers all the lower 
level ingredients to build an event system, so the details of events and 
event handlers are specific to your implementation (Borland), and their 
docs should tell how to use their events, rather than the language itself.

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calling a Event Handler within a class Jens <paule32.jk@gmail.com> - 2022-10-17 22:51 +0200
  Re: calling a Event Handler within a class Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-17 14:32 -0700
  Re: calling a Event Handler within a class Juha Nieminen <nospam@thanks.invalid> - 2022-10-18 07:06 +0000
    Re: calling a Event Handler within a class Jens <paule32.jk@gmail.com> - 2022-10-18 10:06 +0200
      Re: calling a Event Handler within a class Juha Nieminen <nospam@thanks.invalid> - 2022-10-18 09:27 +0000
        Re: calling a Event Handler within a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-10-20 18:36 +0300
      Re: calling a Event Handler within a class David Brown <david.brown@hesbynett.no> - 2022-10-18 11:45 +0200
      Re: calling a Event Handler within a class Manfred <noname@add.invalid> - 2022-10-19 02:43 +0200
  Re: calling a Event Handler within a class Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-18 14:21 +0200
  Re: calling a Event Handler within a class Jens <paule32.jk@gmail.com> - 2022-10-19 12:58 +0200
  Re: calling a Event Handler within a class Lynn McGuire <lynnmcguire5@gmail.com> - 2022-10-20 00:25 -0500

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