NSDate与NSDateFormatter的相关用法

1.NSDateFormatter配合NSDate与NSString之间的转化
  NSDateFormatter有下面2个方法：
  - (NSString *)stringFromDate:(NSDate *)date;//NSDate转NSString
  - (NSDate *)dateFromString:(NSString *)string;//NSString转NSDate
e.g.
 NSString *dateString=@"1900-01-01";
 NSDateFormatter *dateFormatter=[[NSDateFormatter alloc]init];
 [dateFormatter setDateFormat:@"yyyy-MM-dd"];
 NSDate *date=[dateFormatter dateFromString:dateString];
 [dateFormatter release];
 NSString转NSDate与上面类似
 NSString *dateString=[dateFormatter dateFromString:[NSDate date]];
2.NSDateFormatter 的一些格式介绍
  [dateFormatter setDateFormat:@"yyyy年MM月dd日#EEEE"];EEEE为星期几，EEE为周几
  [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
  [dateFormatter setDateFormat:@"yyyy年MMMMd日"];//MMMM 为xx月，一个d可以省去01日前的0
3.NSString转NSDate少一天的解决办法
 用下面这种格式化方式 
  1.[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; 
  2.
   NSCalendar *calendar = [NSCalendar currentCalendar];
   NSDateComponents *components = [calendar components:(NSDayCalendarUnit | NSMonthCalendarUnit |                                  NSYearCalendarUnit) fromDate:[NSDate date]];
   NSDate *todayDate = [calendar dateFromComponents:components];