我的问题是通过NSDateComponents解决的，但是我想了解为什么这个方法如此有效NSDate*today=[NSDatedate];NSLog(@"todayis:%@",today);NSDate*dayChanged=[calendardateBySettingUnit:(NSCalendarUnitDay)value:10ofDate:todayoptions:0];NSLog(@"dayChangedis:%@",dayChanged);NSDate*monthChanged=[calendardateBySettingUnit:(NSCalendarUnitMonth