I was wondering why when you create a repeating timer in a GCD block it doesen't work?
This works fine:
-(void)viewDidLoad{
[super viewDidLoad];
[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(runTimer) userInfo:nil repeats:YES];
}
-(void)runTimer{
NSLog(@"hi");
}
But this doesent work:
dispatch_queue_t myQueue;
-(void)viewDidLoad{
[super viewDidLoad];
myQueue = dispatch_queue_create("someDescription", NULL);
dispatch_async(myQueue, ^{
[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(runTimer) userInfo:nil repeats:YES];
});
}
-(void)runTimer{
NSLog(@"hi");
}
NSTimers are scheduled on the current thread's run loop. However, GCD dispatch threads don't have run loops, so scheduling timers in a GCD block isn't going to do anything.
There's three reasonable alternatives:
+[NSTimer timerWithTimeInterval:target:selector:userInfo:repeats:]
to create the timer and then -[NSRunLoop addTimer:forMode:]
to actually schedule it on the run loop you want to use. This requires having a handle on the run loop in question, but you may just use +[NSRunLoop mainRunLoop]
if you want to do it on the main thread.dispatch_async()
back to the main queue before creating the timer. This is equivalent to option #1 using the main run loop (since it will also create the timer on the main thread).Of course, the real question here is, why are you creating a timer from a GCD queue to begin with?