延時執行的三種方式，延時執行三種方式

延時執行的三種方式，延時執行三種方式

 1 - (void)viewDidLoad 2 { 3     [super viewDidLoad]; 4     // Do any additional setup after loading the view, typically from a nib. 5 } 6  7 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 8 { 9     NSLog(@"-----touchesBegan1-----");10     11 12 13     NSLog(@"-----touchesBegan2-----");14 }15 16 - (void)download:(NSString *)url17 {18     NSLog(@"download------%@---%@", url, [NSThread currentThread]);19 }20 21 - (void)delay322 {23     // 3秒後回到主線程執行block中的代碼24 //    dispatch_queue_t queue = dispatch_get_main_queue();25 //    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{26 //        NSLog(@"------task------%@", [NSThread currentThread]);27 //    });28     29     // 3秒後自動開啟新線程 執行block中的代碼30     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);31     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{32         NSLog(@"------task------%@", [NSThread currentThread]);33     });34 }35 36 - (void)delay237 {38     // 一旦定製好延遲任務後，不會卡主當前線程39     [self performSelector:@selector(download:) withObject:@"http://555.jpg" afterDelay:3];40 }41 42 - (void)delay143 {44     // 順延強制不要用sleep，壞處：卡住當前線程45     [NSThread sleepForTimeInterval:3];46     NSLog(@"-----下載圖片-----");47 }