NSDate 表示该月的第一天

Question

这是一个非常简单的概念，但到目前为止我还无法找到一个优雅的（与日历区域设置无关的）解决方案。我需要找到任意 NSDate 的该月的第一天。例如，给定一个任意 NSDate (任意日期)，将返回另一个 NSDate 对象（我们称之为 firstDayOfMonthDate），它表示该日期的第一天任意日期中的月份。时间部分并不重要，因为我只需要该月第一天的 NSDate 对象（尽管为了整洁起见，如果时间被清零的话会很有用）。

预先感谢您的任何帮助。

Answer 1

一个可能的解决方案：

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *arbitraryDate = [NSDate date];
NSDateComponents *comp = [gregorian components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate:arbitraryDate];
[comp setDay:1];
NSDate *firstDayOfMonthDate = [gregorian dateFromComponents:comp];

Answer 2

NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear 
                                                               fromDate:[NSDate date]];
components.day = 1;
NSDate *firstDayOfMonthDate = [[NSCalendar currentCalendar] dateFromComponents: components];
NSLog(@"First day of month: %@", [firstDayOfMonthDate descriptionWithLocale:[NSLocale currentLocale]]);

Answer 3

Swift 3

我已经包含了获取该月的最后一天的信息，以防它对任何人有用。

extension Date {
    func lastDayOfMonth() -> Date {
        let calendar = Calendar.current
        let dayRange = calendar.range(of: .day, in: .month, for: self)
        let dayCount = dayRange!.count
        var comp = calendar.dateComponents([.year, .month, .day], from: self)

        comp.day = dayCount

        return calendar.date(from: comp)!
    }

    func firstDayOfMonth() -> Date {
        let calendar: Calendar = Calendar.current
        var components: DateComponents = calendar.dateComponents([.year, .month, .day], from: self)
        components.setValue(1, for: .day)
        return calendar.date(from: components)!
    }
}

Answer 4

迅捷版

let arbitraryDate:NSDate = NSDate()
let calendar:NSCalendar = NSCalendar.currentCalendar()
let components:NSDateComponents = calendar.components([.Year, .Month, .Day], fromDate: arbitraryDate)
components.setValue(1, forComponent: .Day)
let firstDayOfMonthDate = calendar.dateFromComponents(components)

Answer 5

斯威夫特3：

let calendar = Calendar.current
var comps = calendar.dateComponents([.year, .month], from: date)
comps.setValue(1, for: .day)
let firstDayOfMonth = calendar.date(from: comps)!

// I tried this, but it doesn't work, why?
// let firstDayOfMonth = calendar.date(bySetting: .day, value: 1, of: date)!