对象在 Swift 中不符合 kvc 时的对象通信

Question

我想创建一个自定义视图，当另一个对象（UIControl 的子类）上发生操作（如更改属性）时显示它

我的方法就是这样

1. 创建一个 UIControl 对象可以遵循的协议
2. 创建我可以观察我的委托的自定义视图

不幸的是，它不起作用，更糟糕的是，它崩溃了，因为编译器说“它不符合 kvc”

贝娄，我的代码：

protocol CustomDelegate: class where Self : UIControl {
    func respondeToControl() -> Bool
}
class CustomView: UIView {
    weak var delegate: CustomDelegate? {
        didSet{
             observeIfControlIsPressed()
       }
   }

   func observeIfControlIsPressed(){
       if delegate != nil {
            let keypath = delegate! as! UIControl

            keypath.addObserver(keypath,
                            forKeyPath: "backgroundColor",
                         options: [NSKeyValueObservingOptions.new, NSKeyValueObservingOptions.old],
            context: nil)

        }
   }

   open override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
       print("background changed")
   }
}

我的问题是，我如何重新设计我的解决方案来实现它 工作吗？

Answer 1

你addObserver错了，“observer”应该是self没有“keypath”

试试这个：

keypath.addObserver(self, forKeyPath: "backgroundColor", options: [.new, .old], context: nil)

Answer 2

您没有正确阅读您的错误。例如：

protocol CustomDelegate : class where Self : UIControl {
    func respondeToControl() -> Bool
}

class CustomView: UIView {
    weak var delegate: CustomDelegate? {
        didSet{
            observeIfControlIsPressed()
        }
    }

    func observeIfControlIsPressed(){
        if delegate != nil {
            let keypath = delegate! as! UIControl

            keypath.addObserver(keypath,
                                forKeyPath: "backgroundColor",
                                options: [NSKeyValueObservingOptions.new, NSKeyValueObservingOptions.old],
                                context: nil)

        }
    }

    open override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        print("background changed")
    }
}

class Foo : UIControl, CustomDelegate {
    func respondeToControl() -> Bool {
        return true
    }
}


class ViewController: UIViewController {

    let testBlock = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()

        let view = CustomView()
        let button = Foo()

        view.delegate = button

        button.backgroundColor = UIColor.red
    }
}

抛出异常：

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '<Meh.Foo: 0x7fc977c1a0c0; baseClass = UIControl; frame = (0 0; 0 0); layer = <CALayer: 0x608000226480>>: An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: backgroundColor

这意味着Foo正在观察foo但没有实现observeValueForKeyPath函数..

现在为什么呢？嗯..这是因为你做到了：

keypath.addObserver(keypath,  //keypath is observing itself..
                    forKeyPath: "backgroundColor",
                    options: [NSKeyValueObservingOptions.new, NSKeyValueObservingOptions.old],
                    context: nil)

keypath 是您的代表......并且正在为其自身添加观察者......

应该是：

keypath.addObserver(self,  //self is observing keypath..
                        forKeyPath: "backgroundColor",
                        options: [NSKeyValueObservingOptions.new, NSKeyValueObservingOptions.old],
                        context: nil)

addObserver的第一个参数需要是要进行观察的类。

该更改将导致它打印：background changed.. 不要忘记稍后删除观察者。