关于倒计时

1，设定一个时间，当前时间与设定时间进行比较，1秒执行一次；

2，设定起始时间和结束时间，把当前时间和起始时间比较，当当前时间大于等于起始时间开始1步骤

self.timer = [NSTimer
timerWithTimeInterval:1
target:self
selector:@selector(timerFireMethod:)
userInfo:nil
repeats:YES];

    [[NSRunLoop
mainRunLoop] addTimer:self.timer
forMode:NSDefaultRunLoopMode];

- (void)timerFireMethod:(NSTimer*)theTimer {

    if (self.startTime &&
self.endTime) {
       
NSDateFormatter *dateFormatter = [[NSDateFormatter
alloc] init];
        dateFormatter.dateFormat =
@"yyyy-MM-dd HH:mm:ss";

        [dateFormatter setTimeZone:[NSTimeZone
timeZoneWithAbbreviation:@"GMT"]];
       
NSDate *startDate = [dateFormatter
dateFromString:self.startTime];
       
NSDate *endDate = [dateFormatter
dateFromString:self.endTime];

       
if ([startDate compare:[self
getNowDateFromatAnDate]] ==
NSOrderedAscending &&
            [endDate
compare:[self
getNowDateFromatAnDate]] ==
NSOrderedDescending) {
           
NSArray *date = [self.endTime
componentsSeparatedByString:@" "];
           
if ([date count] >
1) {
               
NSCalendar *cal = [NSCalendar
currentCalendar];
               
NSDateComponents *time = [[NSDateComponents
alloc] init];

                
               
NSArray *yearArr = [[date
objectAtIndex:0]
componentsSeparatedByString:@"-"];
               
if ([yearArr count] ==
3) {
                    [time
setYear:[[yearArr
objectAtIndex:0]intValue]];
                    [time
setMonth:[[yearArr
objectAtIndex:1]intValue]];
                    [time
setDay:[[yearArr objectAtIndex:2]intValue]];
                }

                
               
NSArray *timeArr = [[date
objectAtIndex:1]
componentsSeparatedByString:@":"];
               
if ([timeArr count] ==
3) {
                    [time
setHour:[[timeArr
objectAtIndex:0]intValue]];
                    [time
setMinute:[[timeArr
objectAtIndex:1]intValue]];
                    [time
setSecond:[[timeArr
objectAtIndex:2]intValue]];
                }
               
NSDate *todate = [cal
dateFromComponents:time];
               
NSDate *today = [NSDate
date];

                

                unsigned
int unitFlags =
NSYearCalendarUnit | NSMonthCalendarUnit |
NSDayCalendarUnit | NSHourCalendarUnit |
NSMinuteCalendarUnit | NSSecondCalendarUnit;
               
NSDateComponents *d = [cal
components:unitFlags fromDate:today
toDate:todate options:0];
               
int hour =[d hour];
               
int minute = [d minute];
               
int second = [d second];
               
if (hour<=0 && minute<=0 && second<=0) {
                   
self.timeLab.text =
@"施工完成";
                    [self
stop];
                }else {
                   
NSString *h =[NSString
stringWithFormat:@"%d",[d
hour]];
                   
NSString *m =[NSString
stringWithFormat:@"%d",[d
minute]];
                   
NSString *s =[NSString
stringWithFormat:@"%d",[d
second]];

                    self.timeLab.text=
[NSString
stringWithFormat:@"%@:%@:%@",h.length!=1?h:[NSString
stringWithFormat:@"0%@",h],m.length!=1?m:[NSString
stringWithFormat:@"0%@",m],s.length!=1?s:[NSString
stringWithFormat:@"0%@",s]];
                }
            }
        }
       
if ([endDate compare:[self
getNowDateFromatAnDate]] ==
NSOrderedAscending) {
           
self.timeLab.text =
@"施工完成";
            [self
stop];
        }
       
if ([startDate compare:[self
getNowDateFromatAnDate]] ==
NSOrderedDescending) {
           
self.timeLab.text =
@"等待施工";
        }
    }
}

- (void)stop
{
   
self.timeLab =
nil;

    [self.timer
invalidate];
   
self.timer =
nil;
}

- (NSDate *)getNowDateFromatAnDate
{
   
NSDate *anyDate = [NSDate
date];

    //设置源日期时区
   
NSTimeZone* sourceTimeZone = [NSTimeZone
timeZoneWithAbbreviation:@"GMT"];

    //设置转换后的目标日期时区
   
NSTimeZone* destinationTimeZone = [NSTimeZone
localTimeZone];

    //得到源日期与世界标准时间的偏移量
   
NSInteger sourceGMTOffset = [sourceTimeZone
secondsFromGMTForDate:anyDate];

    //目标日期与本地时区的偏移量
   
NSInteger destinationGMTOffset = [destinationTimeZone
secondsFromGMTForDate:anyDate];

    //得到时间偏移量的差值
   
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;

    //转为现在时间
   
NSDate* destinationDateNow = [[NSDate
alloc] initWithTimeInterval:interval
sinceDate:anyDate];
   
return destinationDateNow;
}