OC中几种延时操作的比较

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1. sleepForTimeInterval,此函数会卡住当前线程,一般不用

<span style="font-size:18px;">[NSThread sleepForTimeInterval:3];</span>

2. performSelector,定制好延迟任务后，不会卡主"当前线程"(3秒后执行download:方法)

<span style="font-size:18px;">[self performSelector:@selector(download:) withObject:@"http://555.jpg" afterDelay:3];</span>

3.3秒后回到"主线程"执行block中的代码

<span style="font-size:18px;">dispatch_queue_t queue = dispatch_get_main_queue();</span>

<span style="font-size:18px;"><span style="font-size:18px;">dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{    NSLog(@"------task------%@", [NSThread currentThread]);});    dispatch_queue_t queue = dispatch_get_main_queue();dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{    NSLog(@"------task------%@", [NSThread currentThread]);})</span>

4.3秒后自动开启"新线程"执行block中的代码

<span style="font-size:18px;">dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);</span>

<span style="font-size:18px;"><span style="font-size:18px;">dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{    NSLog(@"------task------%@", [NSThread currentThread]);});</span>

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