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无效值的kvo键路径不起作用

key-value-observing swift ios

Robert · 技术社区 · 8 年前

我有问题 keyPathsForValuesAffecting<key> 方法。我想通知观察员 fullName 什么时候? name 或 surname 已经改变了。但不幸的是,观察员没有得到通知。

我的代码:

将要观察的类别:

class DependencyTest: NSObject {
    @objc dynamic var fullName: String {
        return name + " " + surname
    }
    @objc var name = ""
    @objc var surname = ""

    class func keyPathsForValuesAffectingFullName() -> Set<NSObject> {
        return ["name" as NSObject, "surname" as NSObject]
    }
}

观察者视图控制器:

let dep = DependencyTest()

    override func viewDidLoad() {
        super.viewDidLoad()

        addObserver(self, forKeyPath: "dep.fullName", options: .prior, context: nil)

        dep.name = "bob" // Im expecting that `observeValue:` method will be fired
        dep.surname = "gril"

    }

    override func observeValue(forKeyPath keyPath: String?,
                               of object: Any?,
                               change: [NSKeyValueChangeKey : Any]?,
                               context: UnsafeMutableRawPointer?) {
        print("ð¤" + keyPath!) // not called
    }

谢谢!

3 回复 | 直到 8 年前

rob mayoff 8 年前

你需要使用 @objc 在您的 keyPathsForValuesAffecting 方法,以便kvo机器可以使用Objective-C运行时找到它:

@objc class func keyPathsForValuesAffectingFullName() -> Set<NSObject> {
    return ["name, "surname"]
}

顺便说一下,您可以使用一个属性来代替,并且可以使用 #keyPath 使编译器帮助您捕获错误的特殊窗体:

@objc class var keyPathsForValuesAffectingFullName: Set<String> {
    return [#keyPath(name), #keyPath(surname)]
}

你也应该使用 dynamic 上游地产( name 和 surname ,正如肯·托马斯所建议的。

以下是完整的测试程序(作为MacOS命令行程序):

import Foundation

class DependencyTest: NSObject {
    @objc dynamic var fullName: String {
        return name + " " + surname
    }
    @objc dynamic var name = ""
    @objc dynamic var surname = ""

    @objc class var keyPathsForValuesAffectingFullName: Set<String> {
        return [#keyPath(name), #keyPath(surname)]
    }
}

class Observer: NSObject {
    @objc let dep: DependencyTest

    init(dep: DependencyTest) {
        self.dep = dep
        super.init()
        addObserver(self, forKeyPath: #keyPath(Observer.dep.fullName), options: .prior, context: nil)
    }

    deinit {
        removeObserver(self, forKeyPath: #keyPath(Observer.dep.fullName), context: nil)
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        print("kvo: \(keyPath!) \(change?[.notificationIsPriorKey] as? Bool ?? false ? "prior" : "post")")
    }
}

let d = DependencyTest()
let o = Observer(dep: d)
d.name = "Robert"

输出:

kvo: dep.fullName prior
kvo: dep.fullName post
Program ended with exit code: 0

Justin Miller 8 年前

这样可以解决您的问题。

 class ViewController: UIViewController {

    @objc let dep = DependencyTest()

    override func viewDidLoad() {
        super.viewDidLoad()
        self.addObserver(self, forKeyPath: #keyPath(dep.fullName), options: .new, context: nil)
        self.dep.name = "bob" // Im expecting that `observeValue:` method will be fired
        self.dep.surname = "gril"
    }

    override func viewWillDisappear(_ animated: Bool) {
        self.removeObserver(self, forKeyPath: #keyPath(dep.fullName))
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        print("ð¤" + keyPath!) // not called
        print("Full Name = ", dep.fullName)
    }
}

 class DependencyTest: NSObject {
    @objc dynamic var fullName: String = ""
    var name = "" {
        didSet {
            fullName = name + " " + surname
        }
    }
    var surname = "" {
        didSet {
            fullName = name + " " + surname
        }
    }
}

作为函数运行的变量是不可观测的,您必须设置一个实际值。还要记住删除观察者,因为这不是一个本地的swift函数,它不会自动定义,并且可以将您的vc保存到内存中。

Ken Thomases 8 年前

这个 name 和 surname 属性都需要 @objc dynamic 也一样。因为你的 keyPathsForValuesAffectingFullName 方法,kvo在 fullName 被观察到。 @objc 有必要观察它们。 dynamic 必须使swift在每次设置时都实际调用setter(这是kvo挂接的东西),而不是将其内联并只设置backing instance变量。