swift - 如何在单个函数中执行两个完成 block 并将完成 block 的数据传递给下一个 View Controller ？

Question

这是我的数据库结构:

我正在使用一个带闭包的函数，执行两个完成 block 并将数据存储在两个单独的数组中。获得数据后，我想将数据传递到下一个 View Controller 到不同的变量中，但我得到的是两个数组的相同值。

@IBAction func GoToAnswerPage(_ sender: Any) {

    self.getData(refe:JoinCodeTextField.text!) { (array) in
        self.performSegue(withIdentifier:"JoinToAnswerPage",sender:array)
    }

}

func getData(refe: String, completion: @escaping (([Any]) -> ())) {
    var questionArray = [Any]()
    var answerArray = [Any]()
    let ref = Database.database().reference(fromURL: "https://pollapp-30419.firebaseio.com/").child("Questions/\(refe)/")
    ref.child("Question_And_Options").observeSingleEvent(of: .value,with: { snapshot in
        let enumerator = snapshot.children
        while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
            questionArray.append(value)
        }
        completion(questionArray)
    })
    ref.child("Answer_Key").observeSingleEvent(of: .value,with: { snapshot in
        let enumerator = snapshot.children
        while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
            answerArray.append(value)
        }
        completion(answerArray)
    })
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    guard let joinViewController = segue.destination as? JoinAnswerViewController
        else {
            return
    }
    joinViewController.answers = sender as! [String]
    joinViewController.options = sender as! [String]
}

在下一个 View Controller 上。

var options = [Any]()
var answers = [Any]()

这是我得到的输出:

answers-["Test Q-1", "Test A-1", "Test A-2"]

questions-["Test Q-1", "Test A-1", "Test A-2"]

answers-["Test A-1"]

questions-["Test A-1"]

相反，我应该得到:

questions-["Test Q-1", "Test A-1", "Test A-2"]

answers-["Test A-1"]

Answer 1

您的完成处理程序将被调用两次，一次用于“答案”，一次用于“问题”。它们可以以任意顺序出现，因此您应该在完成时传递一个额外的 type 以了解您收到了哪个。使用 [String : [Any]] 字典收集两个数组，并在收到两个数组并存储后调用 self.performSegue(withIdentifier:sender:)它们在字典 arrays 中。

在 prepare(for:sender:) 中解压 sender 字典并赋值:

@IBAction func GoToAnswerPage(_ sender: Any) {

    var arrays = [String : [Any]]()

    self.getData(refe: JoinCodeTextField.text!) { (array, type) in

        arrays[type] = array

        if arrays.count == 2 {
            self.performSegue(withIdentifier:"JoinToAnswerPage",sender: arrays)
        }
    }

}

func getData(refe: String, completion: @escaping (([Any], String) -> ())) {
    var questionArray = [Any]()
    var answerArray = [Any]()
    let ref = Database.database().reference(fromURL: "https://pollapp-30419.firebaseio.com/").child("Questions/\(refe)/")
    ref.child("Question_And_Options").observeSingleEvent(of: .value,with: { snapshot in
        let enumerator = snapshot.children
        while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
            questionArray.append(value)
        }
        completion(questionArray, "question")
    })
    ref.child("Answer_Key").observeSingleEvent(of: .value,with: { snapshot in
        let enumerator = snapshot.children
        while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
            answerArray.append(value)
        }
        completion(answerArray, "answer")
    })
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    guard let joinViewController = segue.destination as? JoinAnswerViewController
        else {
            return
    }

    guard let arrays = sender as? [String : [Any]],
          let answers = arrays["answer"] as? [String],
          let questions = arrays["question"] as? [String]
        else { return }

    joinViewController.answers = answers
    joinViewController.options = questions
}

---

注意:当用户按下按钮时，他们应该立即得到响应。由于您是从网络加载数据，因此可能会有延迟，使用户怀疑是否发生了什么。最好将 JoinCodeTextField.text! 传递给 JoinAnswerViewController 并让它加载问题/答案数据。 JoinAnswerViewController 可以在数据加载时显示一个 UIActivityIndi​​catorView(微调器)，让用户知道数据即将到来。拥有两个数组后，您可以设置 JoinAnswerViewController。