NSDate NSDateFormatter

1.0 获取系统时间和年月日 计算年龄

//获得系统时间

NSDate *  senddate=[NSDate date];

NSDateFormatter  *dateformatter=[[NSDateFormatter alloc] init];

[dateformatter setDateFormat:@"HH:mm"];

NSString *  locationString=[dateformatter stringFromDate:senddate];

//[dateformatter setDateFormat:@"YYYY-MM-dd-HH-mm-ss"];

//NSString *  morelocationString=[dateformatter stringFromDate:senddate];

//获得系统日期

NSCalendar  * cal=[NSCalendar  currentCalendar];

NSUInteger  unitFlags=NSDayCalendarUnit|NSMonthCalendarUnit|NSYearCalendarUnit;

NSDateComponents * conponent= [cal components:unitFlags fromDate:senddate];

NSInteger year=[conponent year];

NSInteger month=[conponent month];

NSInteger day=[conponent day];

NSString *  nsDateString= [NSString  stringWithFormat:@"%4d年%2d月%2d日",year,month,day];

[dateformatter release];

NSDate *senddate=[NSDate date];
        NSCalendar *cal=[NSCalendar currentCalendar];
        NSUInteger unitFlags=NSCalendarUnitDay|NSCalendarUnitMonth|NSCalendarUnitYear;
        NSDateComponents * conponent= [cal components:unitFlags fromDate:senddate];
        NSInteger year=[conponent year];
       
        NSInteger birthYear = [[baseInforModel.birthday substringWithRange:NSMakeRange(0, 4)] integerValue];
       
        NSInteger age = year - birthYear;

NSString *ageStr = [NSString stringWithFormat:@"%tu",age];

2.0 讲一个带时区的时间字符串转换格式成普通时间// 2016-03-04T08:26:33.831Z

// 好使

- (NSString *)htcTimeToLocationStr:(NSString*)strM
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    //输入格式
    [dateFormatter setDateFormat:@"yyyy-MM-dd‘T‘HH:mm:ss.SSSZ"];
    dateFormatter.timeZone = [NSTimeZone timeZoneWithName:@"Asia/Shanghai"];
    NSDate *dateFormatted = [dateFormatter dateFromString:strM];
    [dateFormatter setDateFormat:@"yyyy年MM月dd日 HH:mm:ss"];
    NSString *locationTimeString=[dateFormatter stringFromDate:dateFormatted];
    return locationTimeString;

}

// 没试过这个

NSDateFormatter *format = [NSDateFormatter new];

[format setDateFormat:@"yyyyMMddHHmmss"];

[format setTimeZone:[NSTimeZone timeZoneWithName:@"Asia/Shanghai"]];

NSString *time = [format stringFromDate:[NSDate date]];

return time;

format 用你的字符串的format ，类似 yyyyMMddTHHmmss，记住你中间有个T，

然后再按时时区转下，上面代码是转成中国时区的，你换成GMT，应该就可以了