Le 12 août 09 à 17:55, Christopher Kane a écrit :
On Aug 11, 2009, at 10:28 AM, Fritz Anderson wrote:
iPhone OS 3.0
Can an NSTimer be rescheduled after firing, and after another trip
through the run loop?
I'd like to "reschedule" a NON-repeating timer in my own code. I
assume that in the simple case it would be something like:
- (void) handleTimer: (NSTimer *) aTimer
{
// ... do things ...
[aTimer setFireDate: someTimeInTheFuture];
[[NSRunLoop currentRunLoop] addTimer: aTimer forMode:
NSDefaultRunLoopMode];
}
I'm pretty sure that this is legal — am I right?
No, as you suspected farther down in your message. NSTimers which
are not repeating are one-shot -- they cannot be rescheduled.
Create a new NSTimer, when you next need it, and add it to the run
loop. [And also self.myTimerIvar = nil; in your timer handler as
you thought.]
An alternative would be to create a repeating timer with long interval
and reschedule it as necessary (as explained in the
CFRunLoopTimerSetNextFireDate() reference)
Discussion
Resetting a timer’s next firing time is a relatively expensive
operation and should not be done if it can be avoided; letting timers
autorepeat is more efficient. In some cases, however, manually-
adjusted, repeating timers are useful. For example, if you have an
action that will be performed multiple times in the future, but at
irregular time intervals, it would be very expensive to create, add to
run loop modes, and then destroy a timer for each firing event.
Instead, you can create a repeating timer with an initial firing time
in the distant future (or the initial firing time) and a very large
repeat interval—on the order of decades or more—and add it to all the
necessary run loop modes. Then, when you know when the timer should
fire next, you reset the firing time with
CFRunLoopTimerSetNextFireDate, perhaps from the timer’s own callback
function. This technique effectively produces a reusable, asynchronous
timer.
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