swift - 在 observeValueForKeyPath 中使用开关

Question

我试图通过用单个 switch 语句替换典型的长字符串嵌套 if/else 语句来提高我的 KVO observeValueForKeyPath 实现的易读性。

到目前为止，唯一真正起作用的是:

private let application = UIApplication.sharedApplication()

    switch (object!, keyPath!) {

    case let (object, "delegate") where object as? UIApplication === application:
        appDelegate = application.delegate
        break

    ...

    default:
        super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
    }

如果有的话，它比以下内容更难阅读:

    if object as? UIApplication === application && keyPath! == "delegate" {

    }
    else {

    }

有人有在observeValueForKeyPath(和类似方法)中使用 switch 的好模型吗

编辑:与下面@critik 的问题相关，这里有更多代码来演示仅使用 switch (object as! NSObject, keyPath!){ 的问题:

private let application = UIApplication.sharedApplication()
private var appDelegate : UIApplicationDelegate?
private var rootWindow : UIWindow?

public override func observeValueForKeyPath(
    keyPath: String?,
    ofObject object: AnyObject?,
    change: [String : AnyObject]?,
    context: UnsafeMutablePointer<Void>) {

    switch (object as! NSObject, keyPath!) {
    case (application, "delegate"):
        appDelegate = application.delegate
        (appDelegate as? NSObject)?.addObserver(self, forKeyPath: "window", options: [.Initial], context: nil)
        break

    case (appDelegate, "window"):
        rootWindow = appDelegate?.window?.flatMap { $0 }
        break

    case (rootWindow, "rootViewController"):
        rebuildViewControllerList(rootWindow?.rootViewController)
        break

    default:
        super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
    }
}            

Answer 1

元组上的开关怎么样:

switch (object as! NSObject, keyPath!) {

case (application, "delegate"):
    appDelegate = application.delegate

...

default:
    super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
}

注意 1. 虽然我再次反对 Swift 中的强制转换(向下转换、解包等)，但您可以安全地强制向下转换为 NSObject 而不会发生崩溃，因为每this SO question , KVO 仅适用于 NSObject 子类。

注意 2. 在 Swift 中您也不需要 break，这也会将您的代码至少缩短一行 :)