ios - 类型 "ViewController"的 Swift 值没有名为 "Self"的成员错误

Question

我试图理解 Swift 中的后沿闭包，这段代码在 promptForAnswer() 中给了我一个错误。具体来说，我收到一个 Xcode 错误，其中显示:

Value of type "ViewController" has no member named "Self"

...尽管我已经在代码中声明了它。

有人可以解释一下哪里出了问题吗？

import UIKit
import GameplayKit

var allWords = [String]()
var usedWords = [String]()

class ViewController: UITableViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(promptForAnswer))

        if let startWordsPath = Bundle.main.path(forResource: "start", ofType: "txt") {
            if let startWords = try? String(contentsOfFile: startWordsPath) {
                allWords = startWords.components(separatedBy: "\n")
            }
        } else {
            allWords = ["silkworm"]
        }
        startGame()
    }

    @objc func promptForAnswer() {
        let ac = UIAlertController(title: "Enter answer", message: nil, preferredStyle: .alert)
        ac.addTextField()

        let submitAction = UIAlertAction(title: "Submit", style: .default) {
            [unowned self, ac] (action: UIAlertAction) in
            let answer = ac.textFields![0]
            self.submit(answer: answer.text!) // Value of type "ViewController" has no member type "self"
        }

        ac.addAction(submitAction)
        present(ac, animated: true)
    }

    func startGame() {
        allWords = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: allWords) as! [String]
        title = allWords[0]
        usedWords.removeAll(keepingCapacity: true)
        tableView.reloadData()
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return usedWords.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Word", for: indexPath)
        cell.textLabel?.text = usedWords[indexPath.row]
        return cell
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Answer 1

当我使用默认工具链 (Swift 4.0) 将您的代码粘贴到 Xcode 9.2 中的 Playground 时，我在您指示的行上收到此错误:

Value of type 'ViewController' has no member 'submit'

您可以通过向 Controller 添加如下所示的方法来解决此错误:

func submit(answer: String) {
  // ...
}

也许您使用的任何编译器版本都存在错误。或者也许只是度过了糟糕的一天。有时会发生奇怪的事情。 ́\_(ツ)_/́

即使是 Swift 的小版本，情况也可能发生很大变化，因此请确保包含 Xcode 的版本和您正在使用的工具链。它使重现您的体验变得更加容易。