iOS 本地时间、UTC时间、时间戳等操作、获取当前年月日

//获得当前时间并且转为字符串

- (NSString *)dateTransformToTimeString
{
    NSDate *currentDate = [NSDate date];//获得当前时间为UTC时间 2014-07-16 07:54:36 UTC  (UTC时间比标准时间差8小时)
    //转为字符串
    NSDateFormatter*df = [[NSDateFormatter alloc]init];//实例化时间格式类
    [df setDateFormat:@"yyyy-MM-dd HH:mm:ss"];//格式化
    //2014-07-16 07:54:36(NSString类)
    NSString *timeString = [df stringFromDate:currentDate];
    return timeString;
}

//获取当前时间转为时间戳

- (NSString *)dateTransformToTimeSp
{
    UInt64 recordTime = [[NSDate date] timeIntervalSince1970]*;//客户端当前13位毫秒级时间戳
    NSString *timeSp = [NSString stringWithFormat:@"%llu",recordTime];//时间戳转字符串(13位毫秒级时间戳字符串)
    return timeSp;
}

 //时间戳字符串1469193006001（毫秒）1469193006.001（毫秒，1469193006001234（微秒）1469193006.001234（微秒）转 UTC时间2016-08-11T07:00:55.611Z
 - (NSString *)timespToUTCFormat:(NSString *)timesp
 {
     NSString *timeString = [timesp stringByReplacingOccurrencesOfString:@"." withString:@""];
     if (timeString.length >= ) {
         NSString *second = [timeString substringToIndex:];
         NSString *milliscond = [timeString substringFromIndex:];
         NSString * timeStampString = [NSString stringWithFormat:@"%@.%@",second,milliscond];
         NSTimeInterval _interval=[timeStampString doubleValue];
         NSDate *date = [NSDate dateWithTimeIntervalSince1970:_interval];

         NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
         NSTimeZone *timeZone = [NSTimeZone timeZoneWithName:@"UTC"];
         [dateFormatter setTimeZone:timeZone];
         [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
         NSString *dateString = [dateFormatter stringFromDate:date];

         return dateString;
     }
     return @"";
 }

//13位时间戳1469193006001（毫秒）转 系统时间2016-08-11 08:55:36

 + (NSString *)timespToYMDFormat:(NSNumber *)timesp
 {
     NSString *stime = [timesp stringValue];
     NSTimeInterval time = [[stime substringToIndex:] doubleValue];
     NSDate *detaildate=[NSDate dateWithTimeIntervalSince1970:time];
     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
     [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

     return [dateFormatter stringFromDate: detaildate];
 }

//            时间转时间戳的方法:sendDate为NSDate类

NSString *timeSp = [NSString stringWithFormat:@"%ld", (long)[sendDate timeIntervalSince1970]];

//12-5-11添加

如果只获取当前的年月日，用NSDate 直接截取是不对的，以下方法提供了获取当前的年月日等等

 // 获取代表公历的NSCalendar对象
    NSCalendar *gregorian = [[NSCalendar alloc]
                             initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    // 获取当前日期
    // 定义一个时间字段的旗标，指定将会获取指定年、月、日、时、分、秒的信息
    unsigned unitFlags = NSCalendarUnitYear |
    NSCalendarUnitMonth |  NSCalendarUnitDay |
    NSCalendarUnitHour |  NSCalendarUnitMinute |
    NSCalendarUnitSecond | NSCalendarUnitWeekday;
    // 获取不同时间字段的信息
    NSDateComponents* comp = [gregorian components: unitFlags
                                          fromDate:localeDate];
    NSInteger year = comp.year;

//下面是可以获取的内容 //
@property NSInteger era;
@property NSInteger year;
@property NSInteger month;
@property NSInteger day;
@property NSInteger hour;
@property NSInteger minute;
@property NSInteger second;
@property NSInteger nanosecond NS_AVAILABLE(10_7, 5_0);
@property NSInteger weekday;
@property NSInteger weekdayOrdinal;
@property NSInteger quarter NS_AVAILABLE(10_6, 4_0);
@property NSInteger weekOfMonth NS_AVAILABLE(10_7, 5_0);
@property NSInteger weekOfYear NS_AVAILABLE(10_7, 5_0);
@property NSInteger yearForWeekOfYear NS_AVAILABLE(10_7, 5_0);