iOS --倒计时

#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=5;
//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