不同版本的 Swift 给我错误

Question

所以我一直在观看很多 youtube 视频，目前看来 就像一个版本的 Swift 和另一个版本之间存在巨大的脱节一样。 我从字面上看它一行一行...逐个字符和 一个完全相同的副本给了我类似

的错误

不处理从这里抛出的错误

和

在“守卫”条件下声明的变量在其主体中不可用。

我试图让一个按钮播放 MP3...找到了一个很好的教程，但我写完了代码，它给了我一堆错误...

import AVFoundation
import UIKit

class ViewController: UIViewController {

    @IBOutlet var button: UIButton!

    var player: AVAudioPlayer?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
    @IBAction func didTapButton(){
        if let player = player, player.isPlaying{
            // stop playback

            player.stop()
        }
        else{
            // set up player and play
            let urlString =  Bundle.main.path(forResource: "30 Minute Hockey Mix", ofType: ",m4a")
            do {
                try AVAudioSession.sharedInstance().setMode(.default)
                try AVAudioSession.sharedInstance().setActive(true, options: . notifyOthersOnDeactivation)


                guard let urlString = urlString else {
                    return
                }

                player = try AVAudioPlayer(contentsOf: URL(fileURLWithPath: urlString))

                guard let player = player else {
                    return


                        player.play()

                }
                catch do {
                    print("Error You dumbass")
                }
            }
        }
    }
}

Answer 1

您只是因为在返回后没有 } 而搞砸了，所以 do and try 不再匹配。我在 swift 中注意到的一件事是，当我突然出现一大堆错误时，几乎总是错过了 } 位置。它使编译器真正混淆之后的所有东西。

        do {
            try AVAudioSession.sharedInstance().setMode(.default)
            try AVAudioSession.sharedInstance().setActive(true, options: . notifyOthersOnDeactivation)


            guard let urlString = urlString else {
                return
            }

            player = try AVAudioPlayer(contentsOf: URL(fileURLWithPath: urlString))

            guard let player = player else {
                return
            }

            player.play()

        } catch {
            print("Error You dumbass")
        }

Answer 2

第一个问题是你的一个牙套放错了位置。

应该是这样的：

class ViewController: UIViewController {

    @IBOutlet var button: UIButton!

    var player: AVAudioPlayer?

    @IBAction func didTapButton() {
        if let player = player, player.isPlaying {
            // stop playback

            player.stop()
        } else {
            // set up player and play
            let urlString =  Bundle.main.path(forResource: "30 Minute Hockey Mix", ofType: "m4a")
            do {
                try AVAudioSession.sharedInstance().setMode(.default)
                try AVAudioSession.sharedInstance().setActive(true, options: .notifyOthersOnDeactivation)

                guard let urlString = urlString else {
                    return
                }

                player = try AVAudioPlayer(contentsOf: URL(fileURLWithPath: urlString))

                guard let player = player else {
                    return player.play()
                }
            } // add this
            catch {
                print("Error", error)
            }
        // } remove this
        }
    }
}

如果您选择您的代码 (command+a) 并按 control+i 或选择“Editor ” » “结构” » “重新缩进”，它会格式化你的代码，让你更容易看到错位的大括号在哪里。

无论如何，这解决了“从这里抛出的错误未处理”错误。

第二个错误，“在 'guard' 条件下声明的变量在其主体中不可用”是此代码的结果：

guard let player = player else {
    return player.play()
}

这没有意义。这就是说“如果我不能打开 player，那么 return 它”。也许你的意思是：

if let player = player {
    player.play()
}

或者，更简单地说，您可以使用可选链接，它可以更简洁地实现相同的目的：

player?.play()

因此：

class ViewController: UIViewController {

    @IBOutlet var button: UIButton!

    var player: AVAudioPlayer?

    @IBAction func didTapButton() {
        if let player = player, player.isPlaying {
            // stop playback

            player.stop()
        }
        else{
            // set up player and play
            let urlString = Bundle.main.path(forResource: "30 Minute Hockey Mix", ofType: "m4a")
            do {
                try AVAudioSession.sharedInstance().setMode(.default)
                try AVAudioSession.sharedInstance().setActive(true, options: .notifyOthersOnDeactivation)

                guard let urlString = urlString else {
                    return
                }

                player = try AVAudioPlayer(contentsOf: URL(fileURLWithPath: urlString))

                player?.play()
            } catch {
                print("Error", error)
            }
        }
    }
}

---

我可能会进一步简化：

class ViewController: UIViewController {

    @IBOutlet var button: UIButton!

    var player: AVAudioPlayer?

    @IBAction func didTapButton() {
        if let player = player, player.isPlaying {
            // stop playback

            player.stop()
            return
        }

        // set up player and play
        guard let url = Bundle.main.url(forResource: "30 Minute Hockey Mix", withExtension: "m4a") else {
            return
        }

        do {
            try AVAudioSession.sharedInstance().setMode(.default)
            try AVAudioSession.sharedInstance().setActive(true, options: .notifyOthersOnDeactivation)

            player = try AVAudioPlayer(contentsOf: url)

            player?.play()
        } catch {
            print("Error", error)
        }
    }
}