使用 Cocoa 确定两个日期之间的月数

Question

如何使用 Cocoa 计算两个日期之间的月数？

谢谢， 斯坦

Answer 1

查看 NSCalendars

Answer 2

要获得包含一个月的一部分的答案，可以使用以下命令：

- (NSNumber *)numberOfMonthsBetweenFirstDate:(NSDate *)firstDate secondDate:(NSDate *)secondDate {

if ([firstDate compare:secondDate] == NSOrderedDescending) {
    return nil;
}

NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateComponents *firstDateComponents = [calendar components:NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit
                                                    fromDate:firstDate];

NSInteger firstDay = [firstDateComponents day];

NSRange rangeOfFirstMonth = [calendar rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:firstDate];
NSUInteger numberOfDaysInFirstMonth = rangeOfFirstMonth.length;
CGFloat firstMonthFraction = (CGFloat)(numberOfDaysInFirstMonth - firstDay) / (CGFloat)numberOfDaysInFirstMonth;

// last month component
NSDateComponents *lastDateComponents = [calendar components:NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit
                                                              fromDate:secondDate];
NSInteger lastDay = [lastDateComponents day];
NSRange rangeOfLastMonth = [calendar rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:secondDate];
NSUInteger numberOfDaysInLastMonth = rangeOfLastMonth.length;
CGFloat lastMonthFraction = (CGFloat)(lastDay) / (CGFloat)numberOfDaysInLastMonth;

// Check if the two dates are within the same month
if (firstDateComponents.month == lastDateComponents.month
        && firstDateComponents.year == lastDateComponents.year) {
    NSDateComponents *dayComponents = [calendar components:NSDayCalendarUnit
                                                           fromDate:firstDate
                                                             toDate:secondDate
                                                            options:0];

    NSRange rangeOfMonth = [calendar rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:firstDate];
    NSUInteger numberOfDaysInMonth = rangeOfMonth.length;
    return [NSNumber numberWithFloat:(CGFloat)dayComponents.day / (CGFloat)numberOfDaysInMonth];
}

//  Start date of the first complete month
NSDateComponents *firstDateFirstDayOfNextMonth = firstDateComponents;
firstDateFirstDayOfNextMonth.month +=1;
firstDateFirstDayOfNextMonth.day = 1;

// First day of the last month
NSDateComponents *secondDateFirstDayOfMonth = lastDateComponents;
secondDateFirstDayOfMonth.day = 1;

NSInteger numberOfMonths = secondDateFirstDayOfMonth.month - firstDateFirstDayOfNextMonth.month
        + (secondDateFirstDayOfMonth.year - firstDateFirstDayOfNextMonth.year) * 12;

return [NSNumber numberWithFloat:(firstMonthFraction + numberOfMonths + lastMonthFraction)]; 
}

Answer 3

我必须计算两个日期之间的月份变化。这意味着从 1 月 31 日到 2 月 1 日已经过去了 1 个月，NSCalendar.components 将返回 0。

import UIKit

func monthsSince(from: NSDate, to: NSDate) -> Int {
    let fromComponents = NSCalendar.currentCalendar().components([.Month, .Year], fromDate: from)
    let toComponents = NSCalendar.currentCalendar().components([.Month, .Year], fromDate: to)

    return ((toComponents.year - fromComponents.year) * 12) + (toComponents.month - fromComponents.month)
}

let tests = [
    (from: (day: 1, month: 1, year: 2016), to: (day: 31, month: 1, year: 2016), result: 0),
    (from: (day: 22, month: 1, year: 2016), to: (day: 5, month: 2, year: 2016), result: 1),
    (from: (day: 22, month: 12, year: 2015), to: (day: 1, month: 1, year: 2016), result: 1),
    (from: (day: 1, month: 1, year: 2016), to: (day: 1, month: 2, year: 2016), result: 1),
    (from: (day: 1, month: 1, year: 2016), to: (day: 1, month: 3, year: 2016), result: 2)
]

for test in tests {
    let from = NSCalendar.currentCalendar().dateWithEra(1, year: test.from.year, month: test.from.month, day: test.from.day, hour: 0, minute: 0, second: 0, nanosecond: 0)!
    let to = NSCalendar.currentCalendar().dateWithEra(1, year: test.to.year, month: test.to.month, day: test.to.day, hour: 0, minute: 0, second: 0, nanosecond: 0)!

    if monthsSince(from, to: to) == test.result {
        print("Test \(test), Passed!")
    } else {
        print("Test \(test), Failed!")
    }
}

Answer 4

对于以下示例，组件：fromDate：toDate：选项无法正常工作：

开始日期：2012 年 1 月 1 日
结束日期：2012 年 3 月 31 日。

使用上述方法的月份数 = 2

正确答案应该是 3 个月。

我使用长计算方式如下：
1. 找出起始月份的天数。将其添加到月份的小数部分。如果第一个日期是月初，则将其计为整月。
2. 求最后一个月的天数。将其添加到月份的小数部分如果日期是该月的最后一天，则将其视为完整月份。
3. 找到 2 个日期之间的整个/完整月份并添加到月份的整数部分。
4. 添加整数 &月份的小数部分以获得正确的值。

Answer 5

这是针对 iOS11 更新的 @eliocs 答案的 Objective-C 版本：

- (NSInteger)monthsSince:(NSDate *)from to:(NSDate *)to {
    NSDateComponents *fromComponents = [[NSCalendar currentCalendar] components:NSCalendarUnitMonth | NSCalendarUnitYear fromDate:from];
    NSDateComponents *toComponents = [[NSCalendar currentCalendar] components:NSCalendarUnitMonth | NSCalendarUnitYear fromDate:to];

    return ((toComponents.year - fromComponents.year) * 12) + (toComponents.month - fromComponents.month);
}

Answer 6

NSInteger month = [[[NSCalendar currentCalendar] components: NSCalendarUnitMonth
                                                   fromDate: yourFirstDate
                                                     toDate: yourSecondDate
                                                    options: 0] month];