iOS获取NSDate的年月日

开发中我们有的时候会对日期时间进行大小比较，时间格式化，时间的年份，月份，天进行处理，关于获取NSDate的的年月日目前有两种解决方式:
1.NSDateFormat获取

    NSDate *date =[NSDate date];// FlyElephant
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];

    [formatter setDateFormat:@"yyyy"];
    NSInteger currentYear=[[formatter stringFromDate:date] integerValue];
    [formatter setDateFormat:@"MM"];
    NSInteger currentMonth=[[formatter stringFromDate:date]integerValue];
    [formatter setDateFormat:@"dd"];
    NSInteger currentDay=[[formatter stringFromDate:date] integerValue];
    
    NSLog(@"currentDate = %@ ,year = %ld ,month=%ld, day=%ld",date,currentYear,currentMonth,currentDay);

2.NSDateComponents获取

    NSDate  *currentDate = [NSDate date];
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *components = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:currentDate];
    
    NSInteger year=[components year];
    NSInteger month=[components month];
    NSInteger day=[components day];
    NSLog(@"currentDate = %@ ,year = %ld ,month=%ld, day=%ld",currentDate,year,month,day);

以上两种方式都能轻松获取年月日，iOS默认的NSDate是格林尼治时间，比中国时区的时间少8个小时，处理过日期的都知道8个小时的误差存在，我们在获取年月日的时候不要加上8个小时，iOS系统会自动帮我们自动加上八个小时，以下是个人测试代码:

    // FlyElephant
    NSString *dateString = @"2016-03-31 23:59:00";
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    
    NSDate *mydate=[formatter dateFromString:dateString];
    [formatter setDateFormat:@"yyyy"];
    NSInteger currentYear=[[formatter stringFromDate:mydate] integerValue];
    [formatter setDateFormat:@"MM"];
    NSInteger currentMonth=[[formatter stringFromDate:mydate]integerValue];
    [formatter setDateFormat:@"dd"];
    NSInteger currentDay=[[formatter stringFromDate:mydate] integerValue];
    
    NSLog(@"currentDate = %@ ,year = %ld ,month=%ld, day=%ld",mydate,currentYear,currentMonth,currentDay);
    
    
    NSString *dateStr= @"2016-04-01 00:01:00";
    NSDateFormatter *nextformatter = [[NSDateFormatter alloc] init] ;
    [nextformatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    
    NSDate *date=[nextformatter dateFromString:dateStr];
    [nextformatter setDateFormat:@"yyyy"];
    NSInteger year=[[nextformatter stringFromDate:date] integerValue];
    [nextformatter setDateFormat:@"MM"];
    NSInteger month=[[nextformatter stringFromDate:date]integerValue];
    [nextformatter setDateFormat:@"dd"];
    NSInteger day=[[nextformatter stringFromDate:date] integerValue];
    
    NSLog(@"currentDate = %@ ,year = %ld ,month=%ld, day=%ld",date,year,month,day);

最终输出的结果:

currentDate = 2016-03-31 15:59:00 +0000 ,year = 2016 ,month=3, day=31

currentDate = 2016-03-31 16:01:00 +0000 ,year = 2016 ,month=4, day=1

NSDate对象存放的日期始终是UTC的标准时间，如果想获取本地时间可以根据时间偏移量计算，不过最终的时区还是GMT时区.

- (NSDate *)getCurrentLocalDate:(NSDate *)date {
    NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"];//或GMT
    NSTimeZone *destinationTimeZone = [NSTimeZone localTimeZone];

    NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:date];

    NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:date];
    NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
    
    NSDate *destinationDateNow = [[NSDate alloc] initWithTimeInterval:interval sinceDate:date];
    
    return destinationDateNow;
}