多线程

OC中创建线程的方法
如果指定在主线程中执行代码，如何延时执行代码

• 1.创建线程的方法

  • NSThread
  • NSOperationQueue、NSOperation
  • GCD

• 2.在主线程中执行代码

[self performSelector: onThread:[NSThread mainThread] withObject: waitUntilDone:];
dispatch_async(dispatch_get_main_queue(), ^{});

• 3.延时执行

double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 
(int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){        
});

[self performSelector: withObject: afterDelay:];
[NSTimer scheduledTimerWithTimeInterval: target: selector: userInfo: repeats:];