swift4|swift4 kvc swift4kvc

问题在swift4中使用kvc:

class Person: NSObject { var dog: Dog? } class Dog: NSObject { var name: String init(name: String) { self.name = name } }let whiteDog = Dog(name: "white") let person = Person() person.setValue(whiteDog, forKey: "dog") let myDog: Dog = person.value(forKeyPath: "dog") as! Dog print(myDog.name) 复制代码

然后会发生crash得到如下信息：

Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key dog.' 复制代码

原因 swift为了性能优化，需要标记为@objc的属性才能使用kvc，所以这样:

class Person: NSObject { @objc var dog: Dog? } 复制代码

swift4 新功能无论结构体还是类都可以使用这个方法[keyPath: ReferenceWritableKeyPath]进行取赋值。

class Person { var dog: Dog init(dog: Dog) { self.dog = dog } } class Dog { var name: String init(name: String) { self.name = name } } // let blackDog = Dog(name: "black") let whiteDog = Dog(name: "white") let person = Person(dog: blackDog) person[keyPath: \Person.dog] = whiteDoglet mydog = person[keyPath: name] print(mydog.name) // 打印white 复制代码

将person改为结构体依然可以：