斯威夫特-NSURL fileURLWithPath没有打开? [英] Swift - NSURL fileURLWithPath not unwrapped?

问题描述

非常简单的一个:我在这两行中都得到了"Value of optional type 'NSURL?' not unwrapped."，我正试图从现有的Objective-C应用程序之一中进行翻译:

Pretty simple one: I'm getting "Value of optional type 'NSURL?' not unwrapped." on these two lines, which I'm trying to translate from one of my existing Objective-C apps:

func urlForScene(sceneID:Scene) -> NSURL {
    var filename:NSString = "Whatever"
    let path = NSBundle.mainBundle().pathForResource(filename, ofType: "m4a")
    return NSURL.fileURLWithPath(path)
} 

我认为这很容易做到，而path可能为nil，但是我还没有找到其他让我知道我应该在这里做什么的问题.抱歉，这是一个愚蠢的问题.

I assume this is probably something blindingly simple to do with the possibility of the path being nil, but I've not found any other questions which let me know what I should be doing here. Apologies if it's a stupid question.

如果未打开NSURL，我应该打开它吗?我需要以不同的方式拨打fileURLWithPath:吗?

If the NSURL isn't unwrapped, should I unwrap it? Do I need to call fileURLWithPath: differently?

谢谢.

推荐答案

这是问题所在:urlForScene返回NSURL，而fileURLWithPath:返回可选的NSURL?，(按照文档).

Here's the issue : urlForScene returns a NSURL, whereas fileURLWithPath: returns an optional : NSURL?, (as per the doc).

因此，问题在于，fileURLWithPath:可能返回nil(这就是为什么它返回NSURL?的原因)，并且您返回了非null对象(a NSURL).

So, the issue is, fileURLWithPath: might return nil (this is why it returns a NSURL?), and you return a non-nil object (a NSURL).

编译器告诉您解开它，但我想您最好返回NSURL?并稍后在代码中进行检查.

The compiler tells you to unwrap it, but I'd say you'd better return a NSURL? and check it later on in your code.

此外，您不应使用NSObject.someInitializer(anObject)，而应使用NSObject(initializer:anObject).根据您的情况，将NSURL.fileURLWithPath(path)替换为NSURL(fileURLWithPath:path).

Plus, you shouldn't use NSObject.someInitializer(anObject), but NSObject(initializer:anObject). In your case, replace NSURL.fileURLWithPath(path)by NSURL(fileURLWithPath:path).

总而言之，这是工作代码:

To summarize, here's the working code :

func urlForScene(sceneID:Scene) -> NSURL? {
    let filename = "Whatever"

    let path = NSBundle.mainBundle().pathForResource(filename, ofType: "m4a")
    if let path = path {
        return NSURL(fileURLWithPath:path)
    } else {
        return nil
    }

/* this would also work, it's a matter of taste :
if let path = NSBundle.mainBundle().pathForResource(filename, ofType: "m4a") {
    return NSURL(fileURLWithPath:path)
}
return nil
*/

} 

let mySceneURL = urlForScene(someScene)
if let mySceneURL = mySceneURL {
    /* use the scene */
} else {
    /* the scene couldn't be intialized */
}

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