问题“尝试？”和AVAudioPlayer

我对AVAudioPlayer有以下问题：

import Foundation //Needed for dispatch_once_t import AVFoundation //Needed to play sounds class 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：

可选类型’AVAudioPLayer？’的值 没有打开; 你的意思是用’！’ 要么 ‘？’？

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？

Answer 1

try? 如您所愿，您的song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，您可以使用try!忽略“do catch” try! ：

 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 }