ios – “尝试？”和AVAudioPlayer的问题

概述我对AVAudioPlayer有以下问题： import Foundation //Needed for dispatch_once_timport AVFoundation //Needed to play soundsclass PlayStartSong { var song: AVAudioPlayer = AVAudioPlayer() var songSta 我对AVAudioPlayer有以下问题：

import Foundation   //Needed for dispatch_once_timport AVFoundation //Needed to play soundsclass PlayStartSong {    var song: AVAudioPlayer = AVAudioPlayer()    var songStarted: Bool = false    class var sharedInstance: PlayStartSong {        struct Static {            static var oncetoken: dispatch_once_t = 0            static var instance: PlayStartSong? = nil        }        dispatch_once(&Static.oncetoken) {            Static.instance = PlayStartSong()        }        return Static.instance!    }    func prepareAudios() {        var path = NSBundle.mainBundle().pathForResource("start-2.0",ofType: "mp3")        song = try? AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: path!))    //Error Here        song.preparetoPlay()        song.numberOfLoops = -1 //Makes the song play repeatedly    }}

在“prepareAudios”函数中指定变量“song”的值的行上,转换为Swift 2.0后出现以下错误：

Value of optional type ‘AVAudioPLayer?’ not unwrapped; dID you mean to use ‘!’ or ‘?’?

但是,在使用建议的修复程序时,它告诉我删除刚刚添加的感叹号.这里的确切问题是什么？

解决方法 试试用？如您所愿,您的歌曲变量必须是可选的：

class PlayStartSong {    var song: AVAudioPlayer?    var songStarted: Bool = false    class var sharedInstance: PlayStartSong {        struct Static {            static var oncetoken: dispatch_once_t = 0            static var instance: PlayStartSong? = nil        }        dispatch_once(&Static.oncetoken) {            Static.instance = PlayStartSong()        }        return Static.instance!    }    func prepareAudios() {        let path = NSBundle.mainBundle().pathForResource("start-2.0",ofType: "mp3")        song = try? AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: path!))        song?.preparetoPlay()        song?.numberOfLoops = -1 //Makes the song play repeatedly    }}

要不使它成为Optional,你可以使用try insIDe do catch：

func prepareAudios() {    do {        let path = NSBundle.mainBundle().pathForResource("start-2.0",ofType: "mp3")        song = try AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: path!))        song.preparetoPlay()        song.numberOfLoops = -1 //Makes the song play repeatedly    } catch {        print(error)    }}

此外,如果您完全确定创建AVAudioPlayer实例将始终成功,则可以使用try！忽略“do catch”：

func prepareAudios() {    let path = NSBundle.mainBundle().pathForResource("start-2.0",ofType: "mp3")    song = try! AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: path!))    song.preparetoPlay()    song.numberOfLoops = -1 //Makes the song play repeatedly}

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