IOS development code sharing with Nstimer to achieve the countdown function _ios

With Nstimer implementation countdown function, nonsense not much said, directly on the code, detailed explanation please refer to comments

[Nstimer scheduledtimerwithtimeinterval:1.0 target:self selector: @selector (timerfiremethod:) Userinfo:nil Repeats 
: YES]; 
 /-(void) Timerfiremethod: (Nstimer *) Thetimer {    bool Timestart = YES;     nscalendar *cal = [Nscalendar currentcalendar];//defines a Nscalendar object      Nsdatecomponents *endtime = [[Nsdatecomponents alloc] init];   //initialization target time ...      NSDate *today = [nsdate date];   //Get current time            
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) {//from the NSDate to take out the month, time seconds, but only once         
 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 (one, 2)] intValue];         minute = [[Overdate substringwithrange:nsmakerange (2)] IntValue 
];         second = [[Overdate substringwithrange:nsmakerange (2)] IntValue 
];    &nbsP;    timestart= NO; 
   &NBSP}           [endtime setyear:year]; 
    [endtime Setmonth:month]; 
    [endtime Setday:day]; 
    [endtime Sethour:hour]; 
    [endtime Setminute:minute]; 
    [endtime Setsecond:second];     nsdate *overtime = [cal Datefromcomponents:endtime]; The target time is loaded into date     //is used to get the specific time difference, which is to unify into the Beijing times     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] <) {        fen = [NSString 
stringwithformat:@ "0%d", [D minute]]; 
&NBSP;&NBSP;&NBSP;&NBSP}     nsstring *miao = [NSString stringwithformat:@ "%d", [d second]];     if ([D Second] <) {        miao = [NSString 
stringwithformat:@ "0%d", [d second]]; 
&NBSP;&NBSP;&NBSP;&NBSP}//    NSLog (@ "===%@ day%@:%@:%@", T,h,fen,miao); 
    [_longtime settext:[nsstring stringwithformat:@ "%@ Day%@:%@:%@", T,h,fen,miao];     if ([D second] > 0) {        //Timing is not yet over, Do_ Something//        [_longtime settext:[nsstring stringWithFormat:@ "%@:%@:%@", D 
, Fen,miao]]; &NBSP;&NBSP;&NBSP;&NBSP} else if ([d second] = = 0) {        //Timing End Do_something            &NBSP;&NBSP;&NBSP;&NBSP} else{//timer failure         [thetimer invalidate 
]; &NBSP;&NBSP;&NBSP;&NBSP}      }