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