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                            Using Window Timers
 
You can start a timer with the WinStartTimer function. You supply the window
handle and a time-out value. The function associates the timer with the
specified window. The new timer starts counting down as soon as it is
created. The following code fragment demonstrates starting a timer and
setting it for every half second (500 milliseconds):
 
WinStartTimer(hab,    /* anchor-block handle */
    hwnd,             /* window handle       */
    0,                /* timer ID (not used) */
    500);             /* 500 milliseconds    */
 
You can set the timer anywhere in your application as long as you have a
valid window handle. To process the timer message, you need to add a
WM_TIMER case to the window procedure for the given window. You can use the
case to carry out any actions related to the timer. If the timer is no
longer needed, you can stop it by using the WinStopTimer function. The
following code fragment shows a typical case statement:
 
case WM_TIMER:
        .
        . /* Carry out timer-related tasks. */
        .
 
    WinStopTimer(hab, hwnd, 0);   /* stops the timer for this window */
    return (0L);
 
You can reset the time-out value for the timer for a given window by calling
the WinStartTimer function again. You can reset the timer without stopping
it.
 
If you supply a window handle, you can start only one timer for that window.
If you attempt to create another timer using the same window handle, the
system just resets the time-out for the previous timer. If you need more
than one timer for a window or application, you can create multiple timers
by using a NULL window handle. The WinStartTimer function creates a timer
and returns a timer identifier that uniquely identifies it. The following
code fragment creates two timers:
 
USHORT idTimer1, idTimer2;
 
idTimer1 = WinStartTimer(hab, NULL, 0, 500);
idTimer2 = WinStartTimer(hab, NULL, 0, 1000);
 
Since there is no window associated with these timers, the application must
process the timer messages once they are retrieved from the message queue;
since the timer messages have no window handles, the WinDispatchMsg function
in the message loop cannot dispatch them. The following code fragment shows
a message loop that handles the window timers:
 
HWND hwndTimerHandler; /* handle of window for timer messages */
QMSG qmsg;             /* queue-message structure             */
 
while (WinGetMsg(hab, &qmsg, NULL, 0, 0)) {
    switch(qmsg.msg) {
        case WM_TIMER:
            qmsg.hwnd = hwndTimerHandler;
 
        default:
           WinDispatchMsg(hab, &qmsg);
    }
}
 
If a window receives multiple timer messages, it can use the first message
parameter of the message to identify the timer, because the system copies
the timer identifier to this parameter.
 
If you need to change the time-out value for a timer, you must specify the
timer identifier with the new time-out value. The following code fragment
sets the second timer to 2 seconds:
 
idTimer2 = WinStartTimer(hab, NULL, idTimer2, 2000);
 
When you first start a timer that has no associated window, the
WinStartTimer function creates an arbitrary timer identifier unless you
explicitly provide one. You can request your own timer identifier when you
first start a timer, but you must make sure it is not one of the reserved
system timers.
 
 
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