iOS毫秒倒计时的实现

app开发中，当展示限时优惠的某些商品时，往往会加一个倒计时，提示用户该商品限时优惠所剩的时间，。那对于开发者来说，这就需要我们去实现的是一个倒计时的功能，这个倒计时根据具体需求，可以以天、小时、分、秒、毫秒作单位。

今天呢，主要说说毫秒计时器。我们知道秒和毫秒之间的进制是1000，也就是说1秒=1000毫秒，那我们做毫秒倒计时器的时候是设置一个时间间隔为1毫秒的计时器，逐一减少毫秒数。但是这样的话太耗时了，所以很多的毫秒计时器中的毫秒数只是0-9之间的数字，这就意味着，这个毫秒计时器的时间间隔是100毫秒，这样相比起1毫秒为间隔的计时器，其消耗就少了很多，同时也达到毫秒计时的效果。

那对于整个毫秒倒计时的实现思路就是：得到未来某个日期的时间戳和当前日期的时间戳，计算这两者之间的时间差，然后设置一个时间间隔为100毫秒的计时器，每隔100毫秒，更新一下倒计时器上相应的数值。

自定义一个UIview，将倒计时封装起来。
一、在MsecCountDownView.h中增加时间戳和计时器这两属性

@interface MsecCountDownView : UIView@property(nonatomic, assign)double timeInterval;//未来某个日期的时间戳@property(nonatomic, strong)NSTimer *timer ; //定时器@end

二、在MsecCountDownView.m实现相关UI及倒计时方法

@interface MsecCountDownView (){UIView *countdownBackView;CGFloat _passTime;}@property(nonatomic, strong)UILabel *tipLabel;@property(nonatomic, strong)UILabel *hoursLabel;@property(nonatomic, strong)UILabel *minutesLabel;@property(nonatomic, strong)UILabel *secondsLabel;@property(nonatomic, strong)UILabel *millionSecondsLabel;@property(nonatomic, strong)UILabel *label1;@property(nonatomic, strong)UILabel *label2;@property(nonatomic, strong)UILabel *label3;@property(nonatomic, strong)UILabel *label4;@end

创建相关UI

- (instancetype)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        countdownBackView=[[UIView alloc] initWithFrame:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];        [self addSubview:countdownBackView];        _tipLabel=[[UILabel alloc] init];        _tipLabel.frame = CGRectMake(0, 0, 40, countdownBackView.frame.size.height);        [countdownBackView addSubview:_tipLabel];        _tipLabel.font = [UIFont systemFontOfSize:12];        //小时        _hoursLabel=[[UILabel alloc] initWithFrame:CGRectMake(_tipLabel.frame.origin.x+_tipLabel.frame.size.width, 0, 35, countdownBackView.frame.size.height)];        [countdownBackView addSubview:_hoursLabel];        _hoursLabel.font = [UIFont systemFontOfSize:11];        _label1=[[UILabel alloc] initWithFrame:CGRectMake(_hoursLabel.frame.origin.x+_hoursLabel.frame.size.width, _hoursLabel.frame.origin.y, 8, countdownBackView.frame.size.height)];        [countdownBackView addSubview:_label1];        //分钟        _minutesLabel=[[UILabel alloc] initWithFrame:CGRectMake(_label1.frame.origin.x+_label1.frame.size.width,  _hoursLabel.frame.origin.y, 20, countdownBackView.frame.size.height)];        [countdownBackView addSubview:_minutesLabel];        _minutesLabel.font = [UIFont systemFontOfSize:11];        _label2=[[UILabel alloc] initWithFrame:CGRectMake(_minutesLabel.frame.origin.x+_minutesLabel.frame.size.width,  _hoursLabel.frame.origin.y, 8, countdownBackView.frame.size.height)];        [countdownBackView addSubview:_label2];      //秒        _secondsLabel=[[UILabel alloc] initWithFrame:CGRectMake(_label2.frame.origin.x+_label2.frame.size.width,  _hoursLabel.frame.origin.y, 20 , countdownBackView.frame.size.height)];        [countdownBackView addSubview:_secondsLabel];        _secondsLabel.font = [UIFont systemFontOfSize:11];        _label3=[[UILabel alloc] initWithFrame:CGRectMake(_secondsLabel.frame.origin.x+_secondsLabel.frame.size.width,  _hoursLabel.frame.origin.y, 8 , countdownBackView.frame.size.height)];        [countdownBackView addSubview:_label3];        _millionSecondsLabel=[[UILabel alloc] initWithFrame:CGRectMake(_label3.frame.origin.x+_label3.frame.size.width,  _hoursLabel.frame.origin.y, 20, countdownBackView.frame.size.height)];        [countdownBackView addSubview:_millionSecondsLabel];           //毫秒        _millionSecondsLabel.font = [UIFont systemFontOfSize:11];        _label1.textAlignment=1;        _label2.textAlignment=1;        _label3.textAlignment = 1;        _hoursLabel.textAlignment=1;        _minutesLabel.textAlignment=1;        _secondsLabel.textAlignment=1;        _millionSecondsLabel.textAlignment=1;        _passTime=0.0;    }    return self;}

生成一个计时器

//得到未来某个日期的时间戳，与当前时间戳相比，得到两者的时间差，生成定时器- (void)setTimeInterval:(double)timeInterval{    _timeInterval = timeInterval ;    NSDateFormatter *dataFormatter = [[NSDateFormatter alloc] init];    dataFormatter.dateFormat = @"MM/dd/yyyy HH:mm:ss.SSS";    //获取当前系统的时间，并用相应的格式转换    [dataFormatter stringFromDate:[NSDate date]];    NSString *currentDayStr = [dataFormatter stringFromDate:[NSDate date]];    NSDate *currentDate = [dataFormatter dateFromString:currentDayStr];    //优惠结束的时间，也用相同的格式去转换    NSDate *date = [NSDate dateWithTimeIntervalSince1970:timeInterval/1000.0];    NSString *deadlineStr = [dataFormatter stringFromDate:date];    NSDate *deadlineDate = [dataFormatter dateFromString:deadlineStr];    _timeInterval=[deadlineDate timeIntervalSinceDate:currentDate]*1000;    if (_timeInterval!=0)    {        //时间间隔是100毫秒，也就是0.1秒        _timer = [NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(timerAction) userInfo:nil repeats:YES];        [[NSRunLoop currentRunLoop] addTimer:_timer forMode:UITrackingRunLoopMode];    }else{        [countdownBackView removeFromSuperview];    }}

实现每隔100毫秒执行的方法，更新倒计时器上面相应的数值

// 每间隔100毫秒定时器触发执行该方法- (void)timerAction{    [self getTimeFromTimeInterval:_timeInterval] ;    // 当时间间隔为0时干掉定时器    if (_timeInterval-_passTime == 0)    {        [_timer invalidate] ;        _timer = nil ;    }}// 通过时间间隔计算具体时间(小时,分,秒,毫秒)- (void)getTimeFromTimeInterval : (double)timeInterval{    //1s=1000毫秒    _passTime += 100.f;//毫秒数从0-9，所以每次过去100毫秒    _tipLabel.text=@"还剩：";    _label3.text=@".";    _label2.text=@":";    _label1.text=@":";    //小时数    NSString *hours = [NSString stringWithFormat:@"%ld", (NSInteger)((timeInterval-_passTime)/1000/60/60)];    //分钟数    NSString *minute = [NSString stringWithFormat:@"%ld", (NSInteger)((timeInterval-_passTime)/1000/60)%60];    //秒数    NSString *second = [NSString stringWithFormat:@"%ld", ((NSInteger)(timeInterval-_passTime))/1000%60];    //毫秒数    CGFloat sss = ((NSInteger)((timeInterval - _passTime)))%1000/100;    NSString *ss = [NSString stringWithFormat:@"%.lf", sss];    if (minute.integerValue < 10) {        minute = [NSString stringWithFormat:@"0%@", minute];    }    self.hoursLabel.text = [NSString stringWithFormat:@"%@",hours];    self.minutesLabel.text = [NSString stringWithFormat:@"%@",minute];    self.secondsLabel.text = [NSString stringWithFormat:@"%@",second];    self.millionSecondsLabel.text = [NSString stringWithFormat:@"%@",ss];    if (timeInterval - _passTime <= 0) {        [countdownBackView removeFromSuperview];        [self removeFromSuperview];    }}

三、在ViewController.m给倒计时器赋值，实现自己想要的倒计时

- (void)viewDidLoad {    [super viewDidLoad];    msecView=[[MsecCountDownView alloc] initWithFrame:CGRectMake(50, 100, self.view.frame.size.width-100, 16)];    [self.view addSubview:msecView];    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];    [formatter setDateStyle:NSDateFormatterMediumStyle];    [formatter setTimeStyle:NSDateFormatterShortStyle];    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss.SSS"];    NSDate* date = [formatter dateFromString:@"2017-04-11 15:10:00.000"];    //将日期转换成时间戳    NSInteger timeSp = [[NSNumber numberWithDouble:[date timeIntervalSince1970]] integerValue]*1000;    msecView.timeInterval=timeSp;}

这样就实现倒计时的功能了。但是使用倒计时还需要注意一点，当离开该页面的时候，记得把定时器暂停，等回到该页面的时候再启动倒计时。 这个可以通过以下两方法实现。

-(void)viewWillAppear:(BOOL)animated{//    页面出现时，计时器开始    [msecView.timer setFireDate:[NSDate distantPast]];}-(void)viewWillDisappear:(BOOL)animated{//    页面消失时，暂停提示器    [msecView.timer setFireDate:[NSDate distantFuture]];}

如有需要，可点击demo到github上下载

demo