使用GCD实现倒计时效果

1 #import <UIKit/UIKit.h>2 3 @interface ViewController : UIViewController4 @PRoperty (assign, nonatomic) NSInteger surplusSecond;5 6 @property (strong, nonatomic) IBOutlet UILabel *lblMessage;7 @property (strong, nonatomic) IBOutlet UIButton *btnSendCAPTCHA;8 9 @end

 1 #import "ViewController.h" 2  3 @interface ViewController () 4 - (void)layoutUI; 5 - (void)countDown; 6 @end 7  8 @implementation ViewController 9 #define kSurplusSecond 510 11 - (void)viewDidLoad {12     [super viewDidLoad];13     14     [self layoutUI];15 }16 17 - (void)didReceiveMemoryWarning {18     [super didReceiveMemoryWarning];19     // Dispose of any resources that can be recreated.20 }21 22 - (void)layoutUI {23     _surplusSecond = kSurplusSecond; //剩余秒数；这里指验证码发送完，间隔多少秒才能再次点击「验证」按钮进行发送验证码24     25     _btnSendCAPTCHA.tintColor = [UIColor darkGrayColor];26     _btnSendCAPTCHA.layer.masksToBounds = YES;27     _btnSendCAPTCHA.layer.cornerRadius = 10.0;28     _btnSendCAPTCHA.layer.borderColor = [UIColor grayColor].CGColor;29     _btnSendCAPTCHA.layer.borderWidth = 1.0;30 }31 32 /**33  *  倒计时34  */35 - (void)countDown {36     //全局并发队列37     dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);38     //主队列；属于串行队列39     dispatch_queue_t mainQueue = dispatch_get_main_queue();40     41     //定时循环执行事件42     //dispatch_source_set_timer 方法值得一提的是最后一个参数（leeway），他告诉系统我们需要计时器触发的精准程度。所有的计时器都不会保证100%精准，这个参数用来告诉系统你希望系统保证精准的努力程度。如果你希望一个计时器每5秒触发一次，并且越准越好，那么你传递0为参数。另外，如果是一个周期性任务，比如检查email，那么你会希望每10分钟检查一次，但是不用那么精准。所以你可以传入60，告诉系统60秒的误差是可接受的。他的意义在于降低资源消耗。43     dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, globalQueue);44     dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC, 0.0 * NSEC_PER_SEC);45     dispatch_source_set_event_handler(timer, ^{ //计时器事件处理器46         NSLog(@"Event Handler");47         if (_surplusSecond <= 0) {48             dispatch_source_cancel(timer); //取消定时循环计时器；使得句柄被调用，即事件被执行49             dispatch_async(mainQueue, ^{50                 _btnSendCAPTCHA.enabled = YES;51                 [_btnSendCAPTCHA setTitle:@"验证" forState:UIControlStateNormal];52                 53                 _lblMessage.text = @"使用 GCD 实现倒计时效果";54                 _surplusSecond = kSurplusSecond;55             });56         } else {57             _surplusSecond--;58             dispatch_async(mainQueue, ^{59                 NSString *btnInfo = [NSString stringWithFormat:@"%ld秒", (long)(_surplusSecond + 1)];60                 _btnSendCAPTCHA.enabled = NO;61                 [_btnSendCAPTCHA setTitle:btnInfo forState:UIControlStateDisabled];62             });63         }64     });65     dispatch_source_set_cancel_handler(timer, ^{ //计时器取消处理器；调用 dispatch_source_cancel 时执行66         NSLog(@"Cancel Handler");67     });68     dispatch_resume(timer);  //恢复定时循环计时器；Dispatch Source 创建完后默认状态是挂起的，需要主动恢复，否则事件不会被传递，也不会被执行69 }70 71 - (IBAction)sendCAPTCHA:(id)sender {72     _lblMessage.text = [NSString stringWithFormat:@"验证码发送成功，%d秒后可重新发送", kSurplusSecond];73     74     [self countDown];75 }76 77 @end

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1 2015-08-31 14:40:02.083 KMCountDown[5102:103949] Event Handler2 2015-08-31 14:40:03.087 KMCountDown[5102:103949] Event Handler3 2015-08-31 14:40:04.084 KMCountDown[5102:103949] Event Handler4 2015-08-31 14:40:05.086 KMCountDown[5102:103971] Event Handler5 2015-08-31 14:40:06.085 KMCountDown[5102:103949] Event Handler6 2015-08-31 14:40:07.085 KMCountDown[5102:103949] Event Handler7 2015-08-31 14:40:07.085 KMCountDown[5102:103949] Cancel Handler