在子线程中使用runloop，正确操作NSTimer计时的注意点 三种可选方法

1、第一种方法
 + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo;
2、第二种方法
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(newThread) object:nil];

     [thread start];

 - (void)newThread
{
     @autoreleasepool
     {
         [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(addTime) userInfo:nil repeats:YES];
         [[NSRunLoop currentRunLoop] run];
     }
 }
3、第三种方法
使用了GCD

dispatch_source_t _timers;

     uint64_t interval = 0.01 * NSEC_PER_SEC;
     dispatch_queue_t queue = dispatch_queue_create("my queue", 0);
     _timers = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
     dispatch_source_set_timer(_timers, dispatch_time(DISPATCH_TIME_NOW, 0), interval, 0);
     __weak ViewController *blockSelf = self;
     dispatch_source_set_event_handler(_timers, ^()
     {
         NSLog(@"Timer %@", [NSThread currentThread]);
         [blockSelf addTime];
     });
     dispatch_resume(_timers);
然后再主线程刷新

dispatch_async(dispatch_get_main_queue(), ^{
         self.label.text = [NSString stringWithFormat:@"%.2f", self.timeCount/100];
     });

(以上内容摘自http://www.faceye.net/search/120004.html)