如何在Swfit 4.0中使用键值编码? [英] How do I use Key-Value Coding in Swfit 4.0?

问题描述

我以前从未使用过Swift4，也不知道如何在其中使用KVC.
我尝试用Dictionary创建模型，这里是代码:

I never used Swift4 before, and dont know how to use KVC in it.
I try to create model with Dictionary, here the code:

class Person : NSObject {
    var name: String = ""
    var age: Int = 0

    init(dict: [String : Any]) {
        super.init()
        self.setValuesForKeys(dict)
    }
}

let dict: [String : Any] = ["name" : "Leon", "age" : 18]
let p = Person(dict: dict)
print(p.name, p.age)

我有两个问题:
1.为什么不使用AnyObject? "Leon"和18推断为String和Int，是否在KVC中使用?
2. @objc var name: String = ""，这种形式有效，但是我听不懂.

感谢所有帮助.

There I get two question:
1. Why dont I using AnyObject? "Leon"and18 was infer to String and Int, does it using in KVC?
2. @objc var name: String = "" , this form is worked, but I can not understand it.

Thanks for all helps.

推荐答案

要在Swift 4中为属性实现KVC支持，您需要做两件事:

To implement KVC support for a property in Swift 4, you need two things:

1. 由于KVC的当前实现是用Objective-C编写的，因此需要在属性上使用@objc批注，以便Objective-C可以看到它.这也意味着该属性的类型需要与Objective-C兼容.

1. Since the current implementation of KVC is written in Objective-C, you need the @objc annotation on your property so that Objective-C can see it. This also means that the property's type needs to be compatible with Objective-C.

除了将属性暴露给Objective-C外，您还需要设置通知，以便在属性更改时通知观察者.有三种方法可以做到这一点:

In addition to exposing the property to Objective-C, you will need to set up your notifications in order for observers to be notified when the property changes. There are three ways to do this:

对于存储的属性，最简单的操作是添加dynamic关键字，如下所示:

For stored properties, the easiest thing to do is to add the dynamic keyword like so:

@objc dynamic var foo: String

这将使Cocoa能够使用Objective-C魔术来自动为您生成所需的通知，这通常是您想要的.但是，如果需要更好的控制，还可以手动编写通知代码:

This will allow Cocoa to use Objective-C magic to automagically generate the needed notifications for you, and is usually what you want. However, if you need finer control, you can also write the notification code manually:

@objc private static let automaticallyNotifiesObserversOfFoo = false
@objc var foo: String {
    willSet { self.willChangeValue(for: \.foo) }
    didSet { self.didChangeValue(for: \.foo) }
}

此处的automaticallyNotifiesObserversOf<property name>属性向KVC/KVO系统表示我们正在自行处理通知，可可不应该尝试为我们生成通知.

The automaticallyNotifiesObserversOf<property name> property is there to signify to the KVC/KVO system that we are handling the notifications ourselves and that Cocoa shouldn't try to generate them for us.

最后，如果您的属性未存储，而是依赖于某些其他属性，则需要实现如下的keyPathsForValuesAffecting<your property name here>方法:

Finally, if your property is not stored, but rather depends on some other property or properties, you need to implement a keyPathsForValuesAffecting<your property name here> method like so:

@objc dynamic var foo: Int
@objc dynamic var bar: Int

@objc private static let keyPathsForValuesAffectingBaz: Set<String> = [
    #keyPath(foo), #keyPath(bar)
]
@objc var baz: Int { return self.foo + self.bar }

在上面的示例中，当foo的值或bar的值更改时，将通知baz属性的观察者.

In the example above, an observer of the baz property will be notified when the value for foo or the value for bar changes.

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