ios - 将 swift 2.3 转换为 swift 3 错误

Question

我在 xcode 8.2 中将 swift 2.3 转换为 swift 3

swift 2.3:有代码吗，有代码吗，有代码吗，有代码吗，有代码吗

func playAudio() {
    self.stopAudio()
    let lessonObject:LessonObject = self.lessonArray[self.selectedIndex] as! LessonObject
    let fullPath:String! = Constants.URL_HOST + "\(lessonObject.lessonPath)"
    let soundURL:NSURL! = NSURL.init(string:fullPath)
    let documentsDirectoryURL =  NSFileManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first!
    let destinationUrl = documentsDirectoryURL.URLByAppendingPathComponent(soundURL.lastPathComponent!)
    if NSFileManager().fileExistsAtPath(destinationUrl!.path!) {
        if let soundData = NSData(contentsOfFile: destinationUrl!.path!) {
            self.initAudioWithData(soundData)
        }
        else {
            self.audioErrorAction()
        }
        return
    }
    
    if let soundData = NSData(contentsOfURL:NSURL(string:fullPath)!) {
        self.initAudioWithData(soundData)
    }
    else {
        self.audioErrorAction()
    }
}

swift 3:代码有没有错误？

        func playAudio() {
        self.stopAudio()
        let lessonObject:LessonObject = self.lessonArray[self.selectedIndex] as! LessonObject
        let fullPath:String! = Constants.URL_HOST + "\(lessonObject.lessonPath)"
let soundURL:URL! = URL.init(fileURLWithPath: fullPath)
        let documentsDirectoryURL =  FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
let destinationUrl = documentsDirectoryURL.appendingPathComponent(soundURL.lastPathComponent)
        if FileManager().fileExists(atPath: destinationUrl.path){
            if let soundData = try? Data(contentsOf: URL(fileURLWithPath: destinationUrl.path))
            {
                self.initAudioWithData(soundData)
            }
            else {
                self.audioErrorAction()
            }
            return
        }
if let soundData = try? Data(contentsOf: URL(string:fullPath)!)
        {
            self.initAudioWithData(soundData)
        }
        else {
            self.audioErrorAction()
        }
    }

转换后我的错误:

found nil while unwrapping an Optional value.

I build swift 2.3: destinationUrl = "file:///Users/admin/Library/.../Documents/test.mp3" 0x00006080002a73e0

I build swift 3: destinationUrl = "file:///Users/admin/Library/.../Documents/Optional(%22test.mp3%22)"

Answer 1

错误的根源在这一行

let fullPath:String! = Constants.URL_HOST + "\(lessonObject.lessonPath)"

首先——尽管与问题无关——不要注释编译器可以推断的类型。您将一个好的非可选字符串变成了一个较差的隐式解包可选字符串。

属性 lessonPath 显然也是一个(隐式解包)可选的。使用 String Interpolation 你会得到文字 "Optional(foo)"。如果属性可能为 nil，则需要解包可选或使用可选绑定(bind)。如果值永远不能为 nil

，请考虑非可选属性

let fullPath = Constants.URL_HOST + "\(lessonObject.lessonPath!)"

有关更多信息，请阅读 Swift 3 incorrect string interpolation with implicitly unwrapped Optionals

永远不要将属性声明为隐式展开的可选值 避免编写初始化程序。