暂停循环，直到在 Swift 中获得 UIAlertController 的响应

Question

我一直在尝试从 UIAlertController 的用户那里得到答案。问题是显示 UIAlertController 时代码仍在运行。我想显示警报，然后等到用户给出答案才能继续代码。

func showPopUp(name:String)->String{
   var gender = ""
   let alert = UIAlertController(title: "What are you "+name+"?", message: nil, preferredStyle: .alert)

   alert.addAction(UIAlertAction(title: "Boy", style: .default, handler: { action in
       gender = "Boy"
   }))

   alert.addAction(UIAlertAction(title: "Girl", style: .default, handler: { action in
       gender = "Girl"
   }))

   self.present(alert, animated: true)
   return gender
}

override func viewDidLoad() {
    super.viewDidLoad()
    print("This should appear before the alert")
    var characters: [String] = ["John", "Tom", "Martha"]
    for ch in characters{
       let a = showPopUp(name: ch)
       print(ch + " is a "+ a)
    }
}

我无法将代码放在警报的操作中，因为它在 for 循环中，因此它会在没有获取性别的情况下继续。

Answer 1

您需要使用完成处理程序，因为用户输入是异步发生的，所以您不能 return 使用同步 return。

与您的问题无关，但您应该使用字符串插值而不是 + 来连接字符串。

func showPopUp(name:String, genderCompletion: @escaping (String)->()) {
    let alert = UIAlertController(title: "What are you \(name)?", message: nil, preferredStyle: .alert)

    alert.addAction(UIAlertAction(title: "Boy", style: .default, handler: { action in
        genderCompletion("Boy")
    }))

    alert.addAction(UIAlertAction(title: "Girl", style: .default, handler: { action in
        genderCompletion("Girl")
    }))

    self.present(alert, animated: true)
}

override func viewDidLoad() {
    super.viewDidLoad()
    let characters: [String] = ["John", "Tom", "Martha"]
    for ch in characters{
        showPopUp(name: ch, genderCompletion: { gender in
            print("\(ch) is a \(gender)")
        })
    }
}

暂停循环，直到在 Swift 中获得 UIAlertController 的响应

Pause for loop until getting the response of an UIAlertController in Swift

alert

for-loop

swift

pause