SwiftDate 和日期计算

Question

我正在尝试计算宠物存活的周数和天数。我正在为此使用 SwiftDate。所以我让用户 select 一个生日并将其与当前日期进行比较。

我不想比较时间...所以生日和当前日期应该是同一时间。

我的代码是：

let greg = Calendar(identifier: .gregorian)
var date1 = birthday // from datepicker
var date2 = Date()
var components1 = greg.dateComponents([.year, .month, .day, .hour, .minute, .second], from: date1)
var components2 = greg.dateComponents([.year, .month, .day, .hour, .minute, .second], from: date2)
components1.hour = 15
components1.minute = 0
components1.second = 0
components2.hour = 15
components2.minute = 0
components2.second = 0
date1 = greg.date(from: components1)!
date2 = greg.date(from: components2)!

let daysAlive = (date2 - date1).in(.day)
let weeksAlive = Int(weeksAlive! / 7)
let restDays = daysAlive! - (weeksAlive * 7)
let aLive = "Age: \(weeksAlive) wk, \(restDays) d (\(daysAlive!) d)"

输出为"Age: 28 wk, 3 d (199 d)"

代码有效...但我该如何重构它？有没有更简单的方法来为两个给定日期设置 'same time'？

Answer 1

如果你不在乎时差，为什么不把时间完全去掉呢？它会给你相同的输出，并且只会让你免于输入默认时间值，然后在你的函数的其余部分忽略它们：

let greg = Calendar(identifier: .gregorian)
var date1 = birthday // from datepicker
var date2 = Date()
var components1 = greg.dateComponents([.year, .month, .day], from: date1)
var components2 = greg.dateComponents([.year, .month, .day], from: date2)
date1 = greg.date(from: components1)!
date2 = greg.date(from: components2)!

let daysAlive = (date2 - date1).in(.day)
let weeksAlive = Int(weeksAlive! / 7)
let restDays = daysAlive! - (weeksAlive * 7)
let aLive = "Age: \(weeksAlive) wk, \(restDays) d (\(daysAlive!) d)"

Answer 2

要忽略时间，只需省略 .hour、.minute 和 .second

的组成部分

let components1 = greg.dateComponents([.year, .month, .day], from: date1)
let components2 = greg.dateComponents([.year, .month, .day], from: date2)

date1 = greg.date(from: components1)!
date2 = greg.date(from: components2)!

这是一个没有任何第三方库的更简单的解决方案。它使用 Calendar 方法 dateComponents(:from:to: 为 weekOfMonth 和 day 计算一次差值，为 day 计算一次差值。不需要额外的数学运算。

let greg = Calendar(identifier: .gregorian)
var date1 = greg.date(from: DateComponents(year: 2017, month: 6, day: 25))!
var date2 = Date()
var components1 = greg.dateComponents([.year, .month, .day], from: date1)
var components2 = greg.dateComponents([.year, .month, .day], from: date2)

let weeksAndDays = greg.dateComponents([.weekOfMonth, .day], from: components1, to: components2)
let justDays = greg.dateComponents([.day], from: components1, to: components2)

let aLive = "Age: \(weeksAndDays.weekOfMonth!) wk, \(weeksAndDays.day!) d (\(justDays.day!) d)"
// "Age: 28 wk, 3 d (199 d)"

Answer 3

正如其他人所指出的，您只需从日历中获取 .year、.month、.day。您可能还会看到 DateComponentsFormatter 是否可以实现您想要的：

let formatter: DateComponentsFormatter = {
    let _formatter = DateComponentsFormatter()
    _formatter.allowedUnits = [.day, .weekOfMonth]
    _formatter.unitsStyle = .full
    return _formatter
}()

@IBAction func didValueChange(_ picker: UIDatePicker) {
    let calendar = Calendar.current

    let birthDate = calendar.date(from: calendar.dateComponents([.year, .month, .day], from: picker.date))!
    let now = calendar.date(from: calendar.dateComponents([.year, .month, .day], from: Date()))!
    label.text = formatter.string(from: birthDate, to: now)
}

虽然 DateComponentsFormatter 在结果方面有些局限，但它是本地化的，因此在美国语言环境中会出现以下结果：

28 weeks, 3 days

但是，如果您的应用配置为支持其他语言环境，例如德语，则会导致：

28 Wochen und 3 Tage

SwiftDate 和日期计算

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