.Map 从 Swift 2 转换后在 Swift 3 中生成 [T] [英] .Map producing [T] in Swift 3 after Converting from Swift 2

问题描述

我刚刚将一个项目从 Swift 2 转换为 Swift 3 并且出现错误，但我不明白为什么代码有问题:

I just converted a project from Swift 2 to Swift 3 and am getting an error, but I do not understand why the code is a problem:

var imagesInProject : NSArray?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        let paths = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
        print(paths[0])

        if let urls = Bundle.main.urls(forResourcesWithExtension: "png", subdirectory: nil) {
            imagesInProject = urls.filter {$0.lastPathComponent.hasPrefix("AppIcon") == false} .map {$0.lastPathComponent!}
        }

        return true

    }

错误是:'map'产生'[T]'，而不是预期的上下文结果类型'NSArray?'"

The error is: "'map' produces '[T]', not the expected contextual result type 'NSArray?'"

我该如何解决这个问题?我熟悉 .map 但我不完全理解错误或代码是如何错误的(现在)

How do I fix this? I'm familiar with .map but I don't totally understand the error or how the code is wrong (now)

谢谢！

推荐答案

隐式桥接到 Foundation 类型已经从 Swift 3 中删除.您最好为变量使用原生 Swift 类型:

Implicit bridging to Foundation types has been removed from Swift 3. You are better off using native Swift types for your variables:

var imagesInProject : [URL]?

或者如果你不能/不想这样做，无论出于何种原因，添加一个明确的演员:

Or if you can't/don't want to do that for whatever reason, add an explicit cast:

imagesInProject = urls
                    .filter {$0.lastPathComponent.hasPrefix("AppIcon") == false}
                    .map {$0.lastPathComponent} as NSArray

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