iOS实现倒计时的两种方式

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1.使用NSTimer实现倒计时

@interface ViewController ()

//按钮
@property (nonatomic ,strong)UIButton *btn;
//倒计时的总时间
@property (nonatomic ,assign)NSInteger secondsCountDown;
//定时器
@property (nonatomic ,strong)NSTimer *countDownTimer;;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];

self.btn = [UIButton buttonWithType:UIButtonTypeCustom];

self.btn.frame = CGRectMake(100, 100, 100, 100);

self.btn.backgroundColor = [UIColor yellowColor];

[self.btn setTitle:@"获取验证码" forState:UIControlStateNormal];

//设置文字颜色
[self.btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
//添加点击事件
[self.btn addTarget:self action:@selector(startTime) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:self.btn];
}
//使用NSTimer实现倒计时功能
- (void)startTime
{
//设置倒计时总时长

self.secondsCountDown = 5;

/  *  创建一个timer ， 并将它添加到当前线程的RunLoop
   *  这是添加定时器的另一种方式,不过这个需要手动添加,而且当前线程是主线程
 */
//  self.countDownTimer = [NSTimer timerWithTimeInterval:1 target:self selector:@selector(repeat:) userInfo:@{@"key":@"value"} repeats:true];

// [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
//这种方式定义一个定时器虽然很简单,但是有很多的弊端!如果现在在界面上加入一个scrollview的话滚动scrollView时,定时器会停止;原因:因为上面这种创建的定时器默认已经添加到当前的runLoop中了,当前的runloop就是主线程,主线程的runloop默认是开启的,程序默认也只开启这一个runloop,所以会阻塞主线程,造成定时器停止
self.countDownTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(startTimeNSTimer) userInfo:nil repeats:YES];

[self.btn setTitle:[NSString stringWithFormat:@"%ld秒后重新发送",(long)self.secondsCountDown] forState:UIControlStateNormal];

}

//使用NSTimer实现倒计时

- (void)startTimeNSTimer

{

self.secondsCountDown -- ;

self.btn.userInteractionEnabled = NO;

[self.btn setTitle:[NSString stringWithFormat:@"%ld秒后重新发送",(long)self.secondsCountDown] forState:UIControlStateNormal];

if (self.secondsCountDown == 0) {

[self.countDownTimer invalidate];

self.btn.userInteractionEnabled = YES;

[self.btn setTitle:@"重新发送验证码" forState:UIControlStateNormal];

}

}

2.使用GCD实现倒计时

- (void)startTimeGCD
{
//在block内部不可以修改外部变量,需要添加__block进行修饰
//设置倒计时总时长
__block int timeout=10;
//创建队列(全局并发队列)
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);

//回到主线程更新UI

dispatch_async(dispatch_get_main_queue(), ^{

//设置界面的按钮显示 根据自己需求设置

[self.btn setTitle:@"发送验证码" forState:UIControlStateNormal];

self.btn.userInteractionEnabled = YES;

});

}else{

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);

//                [UIView beginAnimations:nil context:nil];

//                [UIView setAnimationDuration:1];

[self.btn setTitle:[NSString stringWithFormat:@"%@秒后重新发送",strTime] forState:UIControlStateNormal];

//                [UIView commitAnimations];

self.btn.userInteractionEnabled = NO;

});

timeout--;

}

});

dispatch_resume(_timer);

}