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Alex Liu wrote:

> when i compile it shows "E2235 member function must be called or its address 
> taken"
> if i remove the TimerFcn declaration in TForm1 (i.e. TIMERPROC 
> TimerFcn(...), i can pass compilation but  cannot access the controls.

You must declare your callback function as 'static'.
Member functions and stand-alone functions are not the same. The formers 
have a 'this' pointer associated with them that do not have the seconds.

Michel
-- 
----------------------------------------
Michel Leunen
mailto: see my homepage.
C++Builder, BCC5.5.1 Web site:
http://www.leunen.com/
----------------------------------------

Michel Leunen wrote:

> You must declare your callback function as 'static'.

Besides, your callback must be declared as:

void CALLBACK TimerFcn(HWND hwnd, UINT uMsg, UINT idEvent, DWORD dwTime);

and call SetTimer() like this:

SetTimer(Handle, 1, 500, &TimerFcn);

Michel
-- 
----------------------------------------
Michel Leunen
mailto: see my homepage.
C++Builder, BCC5.5.1 Web site:
http://www.leunen.com/
----------------------------------------

"Alex Liu" <alexliu@hket.com> wrote in message
news:45c159aa@newsgroups.borland.com...

> I try to write like this but fail:

Asside from the fact that your callback is declared incorrectly to
begin with (and you should be getting additional compiler errors from
the invalid syntax), you can't use a non-static class method as an API
callback directly anyway.  The signatures do not match because of the
hidden 'this' pointer.  To do what you are asking, you shold use the
WM_TIMER message instead of a callback.  In which case, why not just
use the TTimer component instead?  It already wraps SetTimer() for
you:

    __published:
        TTimer *Timer1;
        void __fastcall Timer1Timer(TObject *Sender);


    void __fastcall TForm1::Button1Click(TObject *Sender)
    {
        Timer1->Interval = 500;
        Timer1->Enabled = true;
    }

    void __fastcall TForm1::Timer1Timer(TObject *Sender)
    {
        // update controls as needed...
    }


If you must use a callback, then you will have to declare the method
as static (otherwise, do not declare it as a class method at all) and
then access the form instance via its global pointer, ie:

    private:
        static void CALLBACK TimerFcn(HWND hwnd, UINT uMsg, UINT
idEvent, DWORD dwTime);

    extern TForm1* Form1;


    void __fastcall TForm1::Button1Click(TObject *Sender)
    {
        SetTimer(Handle, 1, 500, (TIMERPROC)TimerFcn);
    }

    void CALLBACK TForm1::TimerFcn(HWND hwnd, UINT uMsg, UINT idEvent,
DWORD dwTime)
    {
        // use global Form1 pointer to update controls as needed, ie:
        // Form1->Label1->Caption = ...;
    }


Gambit