protocols - 我正在尝试在协议(protocol)扩展中使用 "objectWillChange.send()"但它不起作用，知道为什么吗？

Question

我有一个显示玩家列表的 SwiftUI 导航 View 。我设计的 View 模型协议(protocol)如下。

protocol PlayerListStateProviding: ObservableObject {
    var players: [PlayerModel] { get set }
}

protocol PlayerListDeleting {
    var moc: NSManagedObjectContext { get set }
    func delete(at indexSet: IndexSet)
}

extension PlayerListDeleting where Self: PlayerListStateProviding {
    func delete(at indexSet: IndexSet) {
        moc.delete(players.remove(at: indexSet.first!))
        objectWillChange.send() // this doesn't compile with the following error "Value of type 'Self.ObjectWillChangePublisher' has no member 'send'"
    }
}

我不确定这个错误是什么以及如何避免它。但是，当我删除扩展并创建具体类时，我可以毫无问题地发送信号。

Answer 1

要在协议(protocol)中使用默认的可观察对象发布者，您应该将其限制为相应的类型(因为它在 ObservableObject 的扩展中)，如

extension PlayerListDeleting where Self: PlayerListStateProviding,  
               Self.ObjectWillChangePublisher == ObservableObjectPublisher {
    func delete(at indexSet: IndexSet) {
        moc.delete(players.remove(at: indexSet.first!))
        objectWillChange.send()
    }
}

backup