删除Swift 3中的最后一个字符 [英] Delete last character in Swift 3

问题描述

我正在创建一个简单的计算器应用程序，目前正在努力删除我的按钮被点击时的最后一个字符。我正在使用 dropLast（）方法，但我一直收到错误

I'm creating a simple calculator app and currently struggling at deleting the last character when a my button is tapped. I'm using the dropLast() method but I keep getting the error

调用参数＃1缺少参数

Missing Argument for parameter #1 in call

@IBAction func onDelPressed (button: UIButton!)  {
     runningNumber = runningNumber.characters.dropLast()
     currentLbl.text = runningNumber
}

推荐答案

Swift 4（附录）

在Swift中，您可以申请 dropLast （）直接在 String 实例上，不再调用 .characters 来访问 字符串的字符串：

Swift 4 (Addendum)

In Swift, you can apply dropLast() directectly on the String instance, no longer invoking .characters to access a CharacterView of the String:

var runningNumber = "12345"
runningNumber = String(runningNumber.dropLast())
print(runningNumber) // 1234

Swift 3（原始答案）

我假设 runningNumber 是一个 String 实例。在这种情况下， runningNumber.characters.dropLast（）的类型不是 String ，而是 CharacterView ：

Swift 3 (Original answer)

I'll assume runningNumber is a String instance. In this case, runningNumber.characters.dropLast() is not of type String, but a CharacterView:

let foo = runningNumber.characters.dropLast()
print(type(of: foo)) // CharacterView

你需要使用 CharacterView 实例化 String 实例，然后将其分配回类型 String 的属性，例如

You need to use the CharacterView to instantiate a String instance prior to assigning it back to a property of type String, e.g.

var runningNumber = "12345"
runningNumber = String(runningNumber.characters.dropLast())
print(runningNumber) // 1234

即你的情况

@IBAction func onDelPressed (button: UIButton!)  {
  runningNumber = String(runningNumber.characters.dropLast())
  currentLbl.text = runningNumber
}

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