Swift 不支持用作符合协议 AnyObject 的具体类型

发布于11月14日

我使用Swift 2和WeakContainer来存储一组弱对象，就像NSHashTable.weakObjectsHashTable()个

struct WeakContainer<T: AnyObject> {
    weak var value: T?
}

public protocol MyDelegate : AnyObject {

}

然后在我的ViewController中，我声明

public var delegates = [WeakContainer<MyDelegate>]

但这是错误的

不支持将MyDelegate用作符合协议AnyObject的具体类型

我看到错误是WeakContainer将value个成员声明为weak，所以T应该是object.但我也宣布MyDelegate为AnyObject.怎么避开这个？

推荐答案

我也有同样的 idea ，用泛型创建弱容器

class WeakSet<ObjectType>: SequenceType {

    var count: Int {
        return weakStorage.count
    }

    private let weakStorage = NSHashTable.weakObjectsHashTable()

    func addObject(object: ObjectType) {
        guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
        weakStorage.addObject(object as? AnyObject)
    }

    func removeObject(object: ObjectType) {
        guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
        weakStorage.removeObject(object as? AnyObject)
    }

    func removeAllObjects() {
        weakStorage.removeAllObjects()
    }

    func containsObject(object: ObjectType) -> Bool {
        guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
        return weakStorage.containsObject(object as? AnyObject)
    }

    func generate() -> AnyGenerator<ObjectType> {
        let enumerator = weakStorage.objectEnumerator()
        return anyGenerator {
            return enumerator.nextObject() as! ObjectType?
        }
    }
}

用法:

protocol MyDelegate : AnyObject {
    func doWork()
}

class MyClass: AnyObject, MyDelegate {
    fun doWork() {
        // Do delegated work.
    }
}

var delegates = WeakSet<MyDelegate>()
delegates.addObject(MyClass())

for delegate in delegates {
    delegate.doWork()
}

这不是最好的解决方案，因为WeakSet可以用任何类型初始化，如果这种类型不符合AnyObject协议，那么应用程序将崩溃.但我现在看不到更好的解决方案.