Example: Creating a Timer - Win32 Programmer's Reference

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Example: Creating a Timer

The following example uses the SetTimer function to create two timers. The first timer is set for every 10 seconds, the second for every 5 minutes.

// Set two timers.

SetTimer(hwnd, // handle of main window

IDT_TIMER1, // timer identifier

10000, // 10-second interval

(TIMERPROC) NULL); // no timer callback

SetTimer(hwnd, // handle of main window

IDT_TIMER2, // timer identifier

300000, // 5-minute interval

(TIMERPROC) NULL); // no timer callback

To process the WM_TIMER messages generated by these timers, add a WM_TIMER case statement to the window procedure for the hwnd parameter.

case WM_TIMER:

switch (wParam)

{

case IDT_TIMER1:

. // Process the 10-second timer.

return 0;

case IDT_TIMER2:

. // Process the 5-minute timer.

return 0;

}

An application can also create a timer whose WM_TIMER messages are processed not by the main window procedure but by an application-defined callback function, as in the following code sample, which creates a timer and uses the callback function MyTimerProc to process the timer's WM_TIMER messages.

// Set the timer.

SetTimer(hwnd, // handle of main window

IDT_TIMER3, // timer identifier

5000, // 5-second interval

(TIMERPROC) MyTimerProc); // timer callback

The calling convention for MyTimerProc must be based on the Microsoft® Win32® callback function, TimerProc.

If your application creates a timer without specifying a window handle, your application must monitor the message queue for WM_TIMER messages and dispatch them to the appropriate window.

HWND hwndTimer; // handle of window for timer messages

MSG msg; // message structure

while (GetMessage(&msg, // message structure

NULL, // handle of window to receive the message

NULL, // lowest message to examine

NULL)) // highest message to examine

{

// Post WM_TIMER messages to the hwndTimer procedure.

if (msg.message == WM_TIMER)

{

msg.hwnd = hwndTimer;

}

TranslateMessage(&msg); // translates virtual-key codes

DispatchMessage(&msg); // dispatches message to window

}

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