IOS开发代码分享之用nstimer实现倒计时功能

用nstimer实现倒计时功能，废话不多说，直接上代码，详细解释请参照注释

// 
[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]; 
    } 
     
}