代码之家 › 专栏 › 技术社区 › Mitchell

xcode9 swift4致命错误:在展开可选值时意外发现零

swift iphone ios

Mitchell · 技术社区 · 8 年前

当应用程序启动时,我正在尝试播放mp3文件(5秒),我不断收到错误:

线程1:致命错误:在展开可选值时意外发现nil

import UIKit
import AudioToolbox

class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    //create SystemSoundID
    var soundID:SystemSoundID = 0
    let path = Bundle.main.path(forResource: "iPhone100Voice", ofType: "mp3")
    let baseURL = NSURL(fileURLWithPath: path!)
    AudioServicesCreateSystemSoundID(baseURL, &soundID)
    //play
    AudioServicesPlaySystemSound(soundID)

    }

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

}

有人能解释一下我为什么以及如何解决这个问题吗?

4 回复 | 直到 8 年前

vadian 8 年前

检查这些点,所有条件必须为真:

文件是否在项目导航器中?
是 Target Membership 选中文件检查器中的复选框(要获取它,请选择文件并按 1. )
文件名拼写是否正确( iPhone100Voice.mp3 )?

Jogendar Choudhary 8 年前

请检查您的文件名,可能文件名不正确或不在捆绑包中

所以请检查文件名和扩展名。

使用 if let 或 guard 到 unwrap 路径:

override func viewDidLoad() {

    super.viewDidLoad()
    var soundID:SystemSoundID = 0

    if let path = Bundle.main.path(forResource: "iPhone100Voice", ofType: "mp3") {
       let baseURL = NSURL(fileURLWithPath: path)
       AudioServicesCreateSystemSoundID(baseURL, &soundID)
       AudioServicesPlaySystemSound(soundID)
    } else {
        let alert = UIAlertController(title: "Alert", message: "File not found in your bundle", preferredStyle: UIAlertControllerStyle.alert)
        alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.cancel, handler: nil))
        self.present(alert, animated: true, completion: nil)

   }
}

Malleswari 8 年前

播放视频可能对你有帮助。将视频文件添加到项目中时,请确保在文件检查器中选中或未选中目标复选框。

override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(true)


        if  let path = Bundle.main.path(forResource: "video_1523966087401 (1)", ofType: ".mp4"){
            let player = AVPlayer(url: URL(fileURLWithPath: path))
            let playerController = AVPlayerViewController()
            playerController.player = player
            present(playerController, animated: true) {
                player.play()
            }
        }else{
            //show dialog to user

            print("Error: File not found")
        }
    }

-1

Ankur Lahiry 8 年前

! 表示崩溃运算符,它展开可选值。例如,Value there的作用类似于Optional(53)。因此,变量应包含除nil以外的值 path! 尝试展开可选项并在path变量中附加值53。

要解决这个问题,我们可以使用两种方法

使用防护装置,

guard let pathValue = path else {
        return
}

let baseURL = NSURL(fileURLWithPath: pathValue) //no need to use pathValue, if you use then you have to use path!, although it makes no crash now.  
AudioServicesCreateSystemSoundID(baseURL, &soundID)
//play
AudioServicesPlaySystemSound(soundID)

如果path为nil,则它进入块并返回,如果它有值,则继续到下一行。

使用if let,了解 optional binding

if let pathValue = path {
    let baseURL = NSURL(fileURLWithPath: pathValue) //same comment
    AudioServicesCreateSystemSoundID(baseURL, &soundID)
    //play
    AudioServicesPlaySystemSound(soundID)
}

现在,如果路径是可选的,则无法到达块并传递到下一行