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03.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];