在 Swift 中迭代日期范围的最有效方法是什么？

Question

我正在构建一个 Swift 习惯养成应用程序。在某个时刻，用户选择他们想要养成的习惯的持续时间（以天为单位）。用户还可以选择他们想在一周中的哪几天练习它（周日、周一、周二等）。开始日期是他们养成习惯的那一天。

我目前有开始日期和结束日期（基于用户选择的天数）。但是，在该日期范围内，我需要提取用户选择的特定日期的日期。

我的想法是，对于时间间隔（startDate、endDate）内的每个工作日值“x”，返回日历日期。但是，我尝试创建一个 DateInterval，但我无法对其进行迭代，因为它不符合协议“序列”。

有没有一种有效的方法来迭代这个日期范围并提取这些其他日期？有没有更好的方法我还没有想到？

下面是我当前的日期起始代码：

var date = Date()
var duration = 10
let calendar = Calendar.current

let dateEnding = Calendar.current.date(byAdding: .day, value: duration, to: date as Date)!

//Returns a number representing day of the week.  i.e. 1 = Sunday
let weekDay = calendar.component(.weekday, from: date)


//Initializing a time interval, based on user selected duration and start date
let timeInterval = DateInterval.init(start: date, end: dateEnding)

感谢您的帮助...

Answer 1

我们可以利用Strideable协议的力量：

extension Date: Strideable {
    public func distance(to other: Date) -> TimeInterval {
        return other.timeIntervalSinceReferenceDate - self.timeIntervalSinceReferenceDate
    }

    public func advanced(by n: TimeInterval) -> Date {
        return self + n
    }
}

然后在你的函数中：

// Iterate by 1 day
// Feel free to change this variable to iterate by week, month etc.
let dayDurationInSeconds: TimeInterval = 60*60*24
for date in stride(from: startDate, to: endDate, by: dayDurationInSeconds) {
    print(date)
}

输出：

2018-07-19 12:18:07 +0000
2018-07-20 12:18:07 +0000
2018-07-21 12:18:07 +0000
2018-07-22 12:18:07 +0000
2018-07-23 12:18:07 +0000
....

代码取自this proposal

Answer 2

如果我正确理解您的问题，用户将在某些工作日检查并提供持续时间（天数）。

假设你有一个数组中选择的工作日和持续时间，你可以得到匹配日期的列表，如下所示：

// User selected weekdays (1 = Sunday, 7 = Saturday)
var selectedWeekdays = [2, 4, 6] // Example - Mon, Wed, Fri
var duration = 10 // Example - 10 days

let calendar = Calendar.current
var today = Date()
let dateEnding = calendar.date(byAdding: .day, value: duration, to: today)!

var matchingDates = [Date]()
// Finding matching dates at midnight - adjust as needed
let components = DateComponents(hour: 0, minute: 0, second: 0) // midnight
calendar.enumerateDates(startingAfter: today, matching: components, matchingPolicy: .nextTime) { (date, strict, stop) in
    if let date = date {
        if date <= dateEnding {
            let weekDay = calendar.component(.weekday, from: date)
            print(date, weekDay)
            if selectedWeekdays.contains(weekDay) {
                matchingDates.append(date)
            }
        } else {
            stop = true
        }
    }
}

print("Matching dates = \(matchingDates)")

Answer 3

试试这个

let calendar = NSCalendar.currentCalendar()
let startDate = ...
let endDate = ...
let dateRange = calendar.dateRange(startDate: startDate,
                                     endDate: endDate,
                                   stepUnits: .Day,
                                   stepValue: 1)

for date in dateRange {
    print("It's \(date)!")
}