Question

我正在寻找一种方法来获得一个月的第一天（在Swift中）。我想知道它是星期一，星期二等......通过返回相应的数字。

我尝试了许多解决方案，例如获取NSCalendar组件.weekDay但没有人工作。

Example :

print(getTheFirstDate("2016-2-18"))

// Should return : 0 (because the first day of February 2016 is Monday).

任何帮助都会受到赞赏。

Answer 1

您需要首先将字符串转换为日期，然后您可以从该日期获得月份和年份组件，并使用NSCalendar方法dateFromComponents查找该月的第一天/日期。找到该日期后，您可以从中提取工作日日期组件。试试这样：

Xcode 8.2.1•Swift 3.0.2

extension Date {
    var weekday: Int {
        return Calendar.current.component(.weekday, from: self)
    }
    var firstDayOfTheMonth: Date {
        return Calendar.current.date(from: Calendar.current.dateComponents([.year,.month], from: self))!
    }
}
extension String {
    static var dateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"
        return formatter
    }()

    var date: Date? {
        return String.dateFormatter.date(from: self)
    }
}

"2016-2-18".date?.firstDayOfTheMonth.weekday   // 2 = Monday (Sunday-Saturday 1-7)

extension NSDate {
    var weekday: Int {
        return NSCalendar.currentCalendar().component(.Weekday, fromDate: self)
    }
    var firstDayOfTheMonth: NSDate! {
       return  NSCalendar.currentCalendar().dateFromComponents(NSCalendar.currentCalendar().components([.Year,.Month], fromDate: self))
    }
}
extension String {
    var date: NSDate? {
        struct Date {
            static var formatter: NSDateFormatter = {
                let formatter = NSDateFormatter()
                formatter.dateFormat = "yyyy-MM-dd"
                return formatter
            }()
        }
        return Date.formatter.dateFromString(self)
    }
}

"2016-2-18".date?.firstDayOfTheMonth.weekday   // 2 = Monday (Sunday-Saturday 1-7)

Answer 2

您可以使用相应的星期几编号：

var weekday = calendar!.component(NSCalendarUnit.Weekday, fromDate: yourNSDate)
var weekdayName = self.getDayOfWeek(weekday)

然后你可以调用我创建的这个函数，根据传入 getDayOfWeek（）

的数字得到星期几的相应名称。

func getDayOfWeek(weekday:Int) -> String {
        if(weekday == 1) {
            return "Sunday"
        }
        else if(weekday == 2) {
            return "Monday"
        }
        else if(weekday == 3) {
            return "Tuesday"
        }
        else if(weekday == 4) {
            return "Wednesday"
        }
        else if(weekday == 5) {
            return "Thursday"
        }
        else if(weekday == 6) {
            return "Friday"
        }
        else {
            return "Saturday"
        }

    }

如果您使用String作为日期开始，可以将其更改为NSDate，如下所示：

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = /*place date format here*/
let date = dateFormatter.dateFromString(/*your_date_string*/)

Answer 3

我喜欢Leo的答案，但是如果您想将逻辑封装到单个函数中或者不想使用扩展。

编辑：调整代码以利用Leo的伟大建议，并借用他更简洁的创建月份对象的第一个。谢谢，狮子座！

Answer 4

extension Date {
   var startOfWeek: Date {
      let gregorian = Calendar(identifier: .gregorian)
      let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
      return gregorian.date(byAdding: .day, value: 1, to: sunday!)!
   }

   var endOfWeek: Date {
      let gregorian = Calendar(identifier: .gregorian)
      let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
      return gregorian.date(byAdding: .day, value: 7, to: sunday!)!
   }

   var startOfPreviousWeek: Date {
      let gregorian = Calendar(identifier: .gregorian)
      let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
      return gregorian.date(byAdding: .day, value: -6, to: sunday!)!
   }

   var endOfPreviousWeek: Date {
      let gregorian = Calendar(identifier: .gregorian)
      let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
      return gregorian.date(byAdding: .day, value: 0, to: sunday!)!
   }

   var startDateOfMonth: Date {
      return Calendar.current.date(from: Calendar.current.dateComponents([.year, .month], from: Calendar.current.startOfDay(for: self)))!
   }

   var endDateOfMonth: Date {
      return Calendar.current.date(byAdding: DateComponents(month: 1, day: -1), to: self.startDateOfMonth)!
   }

   var getPreviousMonthDate: Date {
      return Calendar.current.date(byAdding: .month, value: -1, to: self)!
   }

   var startDateOfPreviousMonth: Date {
      return getPreviousMonthDate.startDateOfMonth
   }

   var endOfPreviousMonth: Date {
      return getPreviousMonthDate.endDateOfMonth
   }
}

快速获取一个月的第一天

4 个答案: