NStimer 倒计时

1、初始化

+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo;

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo;

 

注：不用scheduled方式初始化的，需要手动addTimer:forMode: 将timer添加到一个runloop中。

　　而scheduled的初始化方法将以默认mode直接添加到当前的runloop中.

 

scheduledTimerWithTimeInterval:(NSTimeInterval)seconds  

预订一个Timer,设置一个时间间隔。

表示输入一个时间间隔对象，以秒为单位，一个>0的浮点类型的值，如果该值<0,系统会默认为0.1

 target:(id)aTarget

表示发送的对象，如self

 selector:(SEL)aSelector

方法选择器，在时间间隔内，选择调用一个实例方法

userInfo:(id)userInfo

此参数可以为nil，当定时器失效时，由你指定的对象保留和释放该定时器。

repeats:(BOOL)yesOrNo

当YES时，定时器会不断循环直至失效或被释放，当NO时，定时器会循环发送一次就失效。

当定时器创建完（不用scheduled的，添加到runloop中后，该定时器将在初始化时指定的timeInterval秒后自动触发。

 

用NSTimer实现倒计时

[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerFireMethod:) userInfo:nil repeats:YES];

  

//

- (void)timerFireMethod:(NSTimer *)theTimer

{

    BOOL timeStart = YES;

    NSCalendar *cal = [NSCalendar currentCalendar];//定义一个NSCalendar对象

    NSDateComponents *endTime = [[NSDateComponents alloc] init];    //初始化目标时间...

    NSDate *today = [NSDate date];    //得到当前时间

      

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate *dateString = [dateFormatter dateFromString:todate];

    NSString *overdate = [dateFormatter stringFromDate:dateString];

//    NSLog(@"overdate=%@",overdate);

    static int year;

    static int month;

    static int day;

    static int hour;

    static int minute;

    static int second;

    if(timeStart) {//从NSDate中取出年月日，时分秒，但是只能取一次

        year = [[overdate substringWithRange:NSMakeRange(0, 4)] intValue];

        month = [[overdate substringWithRange:NSMakeRange(5, 2)] intValue];

        day = [[overdate substringWithRange:NSMakeRange(8, 2)] intValue];

        hour = [[overdate substringWithRange:NSMakeRange(11, 2)] intValue];

        minute = [[overdate substringWithRange:NSMakeRange(14, 2)] intValue];

        second = [[overdate substringWithRange:NSMakeRange(17, 2)] intValue];

        timeStart= NO;

    }

      

    [endTime setYear:year];

    [endTime setMonth:month];

    [endTime setDay:day];

    [endTime setHour:hour];

    [endTime setMinute:minute];

    [endTime setSecond:second];

    NSDate *overTime = [cal dateFromComponents:endTime]; //把目标时间装载入date

    //用来得到具体的时差，是为了统一成北京时间

    unsigned int unitFlags = NSYearCalendarUnit| NSMonthCalendarUnit| NSDayCalendarUnit| NSHourCalendarUnit| NSMinuteCalendarUnit| NSSecondCalendarUnit;

    NSDateComponents *d = [cal components:unitFlags fromDate:today toDate:overTime options:0];

    NSString *t = [NSString stringWithFormat:@"%d", [d day]];

    NSString *h = [NSString stringWithFormat:@"%d", [d hour]];

    NSString *fen = [NSString stringWithFormat:@"%d", [d minute]];

    if([d minute] < 10) {

        fen = [NSString stringWithFormat:@"0%d",[d minute]];

    }

    NSString *miao = [NSString stringWithFormat:@"%d", [d second]];

    if([d second] < 10) {

        miao = [NSString stringWithFormat:@"0%d",[d second]];

    }

//    NSLog(@"===%@天 %@:%@:%@",t,h,fen,miao);

    [_longtime setText:[NSString stringWithFormat:@"%@天 %@:%@:%@",t,h,fen,miao]];

    if([d second] > 0) {

        //计时尚未结束，do_something

//        [_longtime setText:[NSString stringWithFormat:@"%@:%@:%@",d,fen,miao]];

    } else if([d second] == 0) {

        //计时结束 do_something

          

    } else{

//计时器失效

        [theTimer invalidate];

    }

      

}