IOS倒计时

1.在.h文件定义3个变量

   UIButton *m_timeBt;//倒计时

    int secondsCountDown;//倒计时间 60秒

    NSTimer *countDownTimer;

2.在.m文件中操作,在开始的地方调用LoadTime方法。

-(void)LoadTime

{ secondsCountDown = 60;//60秒倒计时

countDownTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timeFireMethod) userInfo:nil repeats:YES];

}

-(void)timeFireMethod{

    secondsCountDown--;

    [m_timeBtsetTitle:[NSStringstringWithFormat:@"重新获取(%d)",secondsCountDown] forState:UIControlStateNormal];

    // [m_timeBt setEnabled:NO];

    if(secondsCountDown==0){

        [countDownTimer invalidate];

         [m_timeBt setEnabled:YES];

        [m_timeBtsetTitle:[NSStringstringWithFormat:@"获取验证码"] forState:UIControlStateNormal];

        [m_timeBtaddTarget:selfaction:@selector(GetAgain:)forControlEvents:UIControlEventTouchUpInside];

        

    }

}

- (IBAction)GetAgain:(id)sender

{

[self  LoadTime];

}

下面增加一个GCD的写法：

#import "ViewController.h"

@interface ViewController (){
    IBOutlet UIButton *l_timeButton;
}


@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    [l_timeButton addTarget:self action:@selector(startTime) forControlEvents:UIControlEventTouchUpInside];
}
-(void)startTime{
    __block int timeout=30; //倒计时时间
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒执行
    dispatch_source_set_event_handler(_timer, ^{
        if(timeout<=0){ //倒计时结束，关闭
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置界面的按钮显示 根据自己需求设置
                [l_timeButton setTitle:@"发送验证码" forState:UIControlStateNormal];
                l_timeButton.userInteractionEnabled = YES;
            });
        }else{
            //            int minutes = timeout / 60;
            int seconds = timeout % 60;
            NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置界面的按钮显示 根据自己需求设置
                NSLog(@"____%@",strTime);
                [l_timeButton setTitle:[NSString stringWithFormat:@"%@秒后重新发送",strTime] forState:UIControlStateNormal];
                l_timeButton.userInteractionEnabled = NO;
                
            });
            timeout--;
            
        }
    });
    dispatch_resume(_timer);
    
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

注意地方 ：button 要设置成Custom类型，不然会不停的闪动