实现 KVO 投诉属性的协议扩展

Question

public class EntityA: NSManagedObject {
  @NSManaged public private(set) var identifier: String
  @NSManaged public private(set) var name: String
}

public class EntityB: NSManagedObject {
  @NSManaged public private(set) var identifier: String
  @NSManaged public private(set) var name: String
}

protocol NodeRepresentable {
    var children: NSArray { get }
    static var childrenKeyPaths: [String] { get }
}


extension NodeRepresentable where Self: NSManagedObject {
    var children: NSArray { //swift compiler doesn't see this as KVC complaint
        return Self.childrenKeyPaths.flatMap { keyPath in
            return self.mutableSetValueForKey(keyPath)
        }
    } 
}

extension EntityA: NodeRepresentable {
    static var childrenKeyPaths: [String] {
        return ["events", "groups", "races"]
    }

    var _children: NSArray { //this is KVC complaint
        return self.children
    }
}

extension EntityB: NodeRepresentable {

    static var childrenKeyPaths: [String] {
        return ["events", "groups", "markets"]
    }

    var _children: NSArray { //this is KVC complaint
        return self.children
    }
}

Compiler doesn't find valueForKey for children on EntityA and EntityB. Protocol extensions don't seem to implement KVO complaint properties. I've tried declaring dynamic properties on protocol but that doesn't work.

Is somehow possible to avoid declaring computed var on each Entity using some type of language feature?

Answer 1

The Swift property extension aren't visible to Objective-C.

Try adding @objc to the declaration. ie @objc var children: ...

see also https://developer.apple.com/forums/thread/122181