Question

以下代码会从日期中添加或减去一个月。在那次操作之后，我想明确地将当月的日期设置为15.我怎样才能实现这一目标？

NSDateComponents* offsetComponents = [[NSDateComponents alloc]init];
int magnitude = isLeft ? 1 : -1;
[offsetComponents setMonth:magnitude];
NSCalendar* calendar1 = [NSCalendar currentCalendar];
updatedDate = [calendar1 dateByAddingComponents:offsetComponents toDate:dateRef options:0];

Answer 1

月份的设置无关紧要且是单独的操作。获取日期的组成部分，更改日期，然后重新组合日期。您可以在更改月份之前或之后执行此操作。

NSDate * today = [NSDate date];
NSCalendar * cal = [NSCalendar currentCalendar];

NSDateComponents * offsetComponents = [NSDateComponents new];
[offsetComponents setMonth:-1];

// Either

NSDate * sameDayLastMonth = [cal dateByAddingComponents:offsetComponents
                                                 toDate:today
                                                options:0];

NSDateComponents * lastMonthComps = [cal components:NSUIntegerMax
                                           fromDate:sameDayLastMonth];
[lastMonthComps setDay:15];

NSDate * fifteenthOfLastMonth = [cal dateFromComponents:lastMonthComps];

// or

NSDateComponents * todayComps = [cal components:NSUIntegerMax
                                       fromDate:today];
[todayComps setDay:15];

NSDate * fifteenth = [cal dateFromComponents:todayComps];

NSDate * fifteenthOfLastMonth = [cal dateByAddingComponents:offsetComponents
                                                     toDate:fifteenth
                                                    options:0];

或者，甚至更容易（呃，我应该首先做到这一点）：

NSDate * today = [NSDate date];
NSCalendar * cal = [NSCalendar currentCalendar];

NSInteger offset = arc4random_uniform(2) ? -1 : 1;

NSDateComponents * comps = [cal components:NSUIntegerMax
                                  fromDate:today];
[comps setDay:15];
[comps setMonth:[comps month] + offset];

NSDate * newDate = [cal dateFromComponents:comps];

在NSDate上更改月中的日期

1 个答案: