IOS开发中延迟执行和取消

self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(delay) userInfo:nil repeats:NO];

[self.timer invalidate];
GCD

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    // ...
});

typedef void (^Task)(BOOL cancel);
Task delay(NSTimeInterval time,void (^task)()) {
  __block void (^closure)() = task;
  __block Task result;
  Task delayedClosure = ^(BOOL cancel){
    if (closure) {
      void (^internalClosure)() = closure;
      if (!cancel) {
        dispatch_async(dispatch_get_main_queue(), internalClosure);
      }
    }
    closure = nil;
    result = nil;
  };
  
  result = delayedClosure;
  
  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(time * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    if (delayedClosure) {
      delayedClosure(NO);
    }
  });
  return result;
}
使用的话可以这样：

delay(60, ^{
  // ...
});

@property (copy, nonatomic) Task task;
self.task = delay(60, ^{
  // ...
});

@property (strong, nonatomic) dispatch_source_t timer;
// 队列
dispatch_queue_t queue = dispatch_get_main_queue();
// 创建 dispatch_source
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
// 声明成员变量
self.timer = timer;
// 设置两秒后触发
dispatch_time_t startTime = dispatch_time(DISPATCH_TIME_NOW, 3.0 * NSEC_PER_SEC);
// 设置下次触发事件为 DISPATCH_TIME_FOREVER
dispatch_time_t nextTime = DISPATCH_TIME_FOREVER;
// 设置精确度
dispatch_time_t leeway = 0.1 * NSEC_PER_SEC;
// 配置时间
dispatch_source_set_timer(timer, startTime, nextTime, leeway);
// 回调
dispatch_source_set_event_handler(timer, ^{
  // ...
});
// 激活
dispatch_resume(timer);