Question

我试图每天从午夜开始尝试从阵列中选择一个新元素，然后一旦使用了所有元素，就跳回到数组的开头。最好的方法是什么？这是我到目前为止所拥有的。

import UIKit

var wordsArray = [String] ()

wordsArray = ["Hallo","Apfel","Geburtstag","Pherd","Angst"]

let date = NSDate ()
let calendar:NSCalendar! = NSCalendar(calendarIdentifier: NSCalendar.Identifier.gregorian)
var dateComponents = DateComponents()
dateComponents.day = 1

while wordsArray (0..<2) {
  gregorian.date(byAdding: NSCalendar.Unit.day, value: $0, to: now, options: NSCalendar.Options(rawValue: 0))
}

Answer 1

要使用模运算符包围数组，它会分配index / number of items in the array并返回除法的其余部分 - 在这种情况下始终为0...4

let wordsArray = ["Hallo","Apfel","Geburtstag","Pferd","Angst"]

for i in 0..<10 {
   print(wordsArray[i % wordsArray.count])
}

在代码中创建索引变量

var index = 0

以这种方式递增

index = (index + 1) % wordsArray.count

Answer 2

如果我理解你，你想每天使用某个数组元素，这些元素应该循环选择。
所以主要问题是如何在午夜每天做点什么这可以使用Timer：

来实现

// First determine coming midnight
let calendar = NSCalendar.current
let nextDay = calendar.date(byAdding: .day, value: 1, to: Date())
let comingMidnight = calendar.startOfDay(for: nextDay!)

// Then start a time coming midnight, and repeat it every day
// Please note that 24 * 60 * 60 is not completely correct considering daylight saving times
// Sometimes days have 23 hours and sometimes 25 hours!
_ = Timer.init(fireAt: comingMidnight, interval: 24 * 60 * 60, target: self, selector: Selector(("timerFired")), userInfo: nil, repeats: true)

// And this is the timer callback:
func timerFired(timer: Timer) {
    // Here you can select the next element in your array, any do what is required
    // For selecting the elements cyclically, see the other answers!
}

此代码尚未经过测试，但它应该让您知道如何继续。

Answer 3

这是我能想到的最简单的方法。

    var wordsArray = [String] ()
    wordsArray = ["Hallo","Apfel","Geburtstag","Pherd","Angst"]
    let secondsInDay = (60 * 60 * 24)
    let dayNumber = Int(NSDate().timeIntervalSince1970 / Double(secondsInDay))
    let selectedNumber = dayNumber % wordsArray.count
    let chosenWord = wordsArray[selectedNumber]
    print(chosenWord)

编辑：希望满足投诉的另一种方法

    var wordsArray = [String] ()
    wordsArray = ["Hallo","Apfel","Geburtstag","Pherd","Angst"]

    let calendar = Calendar(identifier: .gregorian)
    let date = Date()
    let yearNumber = calendar.component(.year, from: date)
    let monthNumber = calendar.component(.month, from: date)
    let dayNumber = calendar.component(.day, from: date)

    let daysInYear = Double(yearNumber) * 12.0 * 365.25
    let daysInMonth = Double(monthNumber) * 30.42
    let totalNumber = daysInYear + daysInMonth + Double(dayNumber)

    let selectedNumber = Int(totalNumber) % wordsArray.count
    let chosenWord = wordsArray[selectedNumber]

    print(chosenWord)

我怎样才能每天打印一个新的数组元素？

3 个答案: