Objective C equivalent to javascripts setTimeout?

问题:

I was wondering whether there is a solution to raise an event once after 30 seconds or every 30 seconds in CocoaTouch ObjectiveC.

回答1:

There are a number of options.

The quickest to use is in NSObject:

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

(There are a few others with slight variations.)

If you want more control or to be able to say send this message every thirty seconds you probably need NSTimer.

回答2:

The performSelector: family has its limitations. Here is the closest setTimeout equivalent:

dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC * 0.5);
dispatch_after(delay, dispatch_get_main_queue(), ^(void){
    // do work in the UI thread here
});

EDIT: A couple of projects that provide syntactic sugar and the ability to cancel execution (clearTimeout):

• https://github.com/Spaceman-Labs/Dispatch-Cancel
• https://gist.github.com/zwaldowski/955123

回答3:

Take a look at the NSTimer class:

NSTimer *timer;
...
timer = [[NSTimer scheduledTimerWithTimeInterval:30.0 target:self selector:@selector(thisMethodGetsFiredOnceEveryThirtySeconds:) userInfo:nil repeats:YES] retain];
[timer fire];

Somewhere else you have the actual method that handles the event:

- (void) thisMethodGetsFiredOnceEveryThirtySeconds:(id)sender {
   NSLog(@"fired!");
}

回答4:

+[NSTimer scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:]

Documentation

You may also want to look at the other NSTimer methods