IOS關於大型網站搶購、距活動結束，剩餘時間倒計時的實現程式碼，程式碼比較簡單，大家根據需求適當的新增修改刪除程式碼

1.定義4個 Label 來接收倒計時:

@property (weak, nonatomic) IBOutlet UILabel *dayLabel;
@property (weak, nonatomic) IBOutlet UILabel *hourLabel;
@property (weak, nonatomic) IBOutlet UILabel *minuteLabel;
@property (weak, nonatomic) IBOutlet UILabel
 
 *secondLabel;

2.在實現檔案中實現方法:

//時間戳轉換為日期格式(毫秒的時間戳)
- (NSString *)timeWithTimeIntervalString:(NSString *)timeString
{
    // 格式化時間
    NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
    formatter.timeZone = [NSTimeZone timeZoneWithName:@"shanghai"];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"
 
];

    // 毫秒值轉化為秒
    NSDate* date = [NSDate dateWithTimeIntervalSince1970:[timeString doubleValue]/ 1000.0];
    NSString* dateString = [formatter stringFromDate:date];
    NSLog(@"時間 === %@",dateString);
    return dateString;
}
-(void)downSecondHandle:(NSString *)aTimeString{

    NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"
 
];


    NSDate *endDate = [dateFormatter dateFromString:[self timeWithTimeIntervalString:aTimeString]]; //結束時間
    NSDate *endDate_tomorrow = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:([endDate timeIntervalSinceReferenceDate])];
    NSDate *startDate = [NSDate date];
        NSString* dateString = [dateFormatter stringFromDate:startDate];
    NSLog(@"現在的時間 === %@",dateString);
    NSTimeInterval timeInterval =[endDate_tomorrow timeIntervalSinceDate:startDate];

    if (_timer==nil) {
        __block int timeout = timeInterval; //倒計時時間

        if (timeout!=0) {
            dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
            _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
            dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒執行
            dispatch_source_set_event_handler(_timer, ^{
                if(timeout<=0){ //倒計時結束，關閉
                    dispatch_source_cancel(_timer);
                    _timer = nil;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        self.dayLabel.text = @"";
                        self.hourLabel.text = @"00";
                        self.minuteLabel.text = @"00";
                        self.secondLabel.text = @"00";
                    });
                }else{
                    int days = (int)(timeout/(3600*24));
                    if (days==0) {
                        self.dayLabel.text = @"";
                    }
                    int hours = (int)((timeout-days*24*3600)/3600);
                    int minute = (int)(timeout-days*24*3600-hours*3600)/60;
                    int second = timeout-days*24*3600-hours*3600-minute*60;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        if (days==0) {
                            self.dayLabel.text = @"0天";
                        }else{
                            self.dayLabel.text = [NSString stringWithFormat:@"%d天",days];
                        }
                        if (hours<10) {
                            self.hourLabel.text = [NSString stringWithFormat:@"0%d",hours];
                        }else{
                            self.hourLabel.text = [NSString stringWithFormat:@"%d",hours];
                        }
                        if (minute<10) {
                            self.minuteLabel.text = [NSString stringWithFormat:@"0%d",minute];
                        }else{
                            self.minuteLabel.text = [NSString stringWithFormat:@"%d",minute];
                        }
                        if (second<10) {
                            self.secondLabel.text = [NSString stringWithFormat:@"0%d",second];
                        }else{
                            self.secondLabel.text = [NSString stringWithFormat:@"%d",second];
                        }

                    });
                    timeout--;
                }
            });
            dispatch_resume(_timer);
        }
    }


}

3.在需要出使用:

 [self downSecondHandle:@"1494622800000"];