前言
大家应该都知道在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。
实现方法
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
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@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
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@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
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- (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
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//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
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// 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
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- (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。
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-(void)viewWillAppear:(BOOL)animated{// 页面出现时，开启计时器 [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，可通过下面两种方法下载demo
总结
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助，如果有疑问大家可以留言交流，谢谢大家对服务器之家的支持。
