Volume 6A: Motif Programming Manual

Output of arrow_timer.c

The program creates up and down ArrowButtons and attaches arm and disarm callbacks that start and stop an internal

timer. Each time the timer expires, the value displayed by the Label changes incrementally by one. The timer remains

on as long as the button is down. We know that the button has been released when the disarm event occurs.

The function responsible for this behavior is start_stop(); it is installed for both the arm and disarm callback.

When the button is pressed, the reason is XmCR_ARM, and the timer starts. When the button is released, the disarm

callback is invoked, the reason is XmCR_DISARM, and the timer is disabled. The start_stop() routine initiates

the timer by calling change_value(). Each time the timer expires, change_value() is also called, which

means that the function is called repeatedly while the button is pressed. The id represents the ID of the timer that

recently expired from the last call to XtAppAddTimeOut(). If the value is one, the function was called from

start_stop(), not as a timeout. We don't restart the timer if the value has reached its maximum or minimum

value. If id is one, we know that this is the initiating call, so we make the first timeout last longer to allow the user to

release the button before getting into the "speedy" timeouts. Otherwise, the time out occurs every 100 milliseconds.

If you experiment with the program, ...