为什么我无法在 SwiftUI 的视图结构内收到有关观察者 class 的通知？

Question

我有以下代码，我在其中创建了一个 class 作为默认通知的观察者。但通知从未到达：

struct NotificationCenterExampleView: View {
    
    let observerA = ObserverClassA()
    
    init() {
        print("NotificationCenterExampleView init")
        
        
        NotificationCenter.default.addObserver(observerA, selector: #selector(ObserverClassA.receivedNotification(notification:)), name: Notification.Name("CustomNotification"), object: "This is the message")
        let notificationToPost = Notification(name: Notification.Name("CustomNotification"), object: "Message being sent", userInfo: nil)
        NotificationCenter.default.post(notificationToPost)
    }
    
    var body: some View {
        Text("Notification Center Example")
            .frame(minWidth: 250, maxWidth: 500, minHeight: 250, maxHeight: 500)
    }
}

class ObserverClassA: NSObject {
    
    @objc func receivedNotification(notification: Notification) {
        let message = notification.object as! String
        print("Message received: \(message)")
    }
}

我知道使用 .publisher 和 onReceive 这将在 View 结构中工作，但这段代码不起作用的真正原因是什么？

Answer 1

通知与对象匹配，因此如果您订阅一个对象但 post 订阅另一个对象，则不会触发订阅者。

这里是固定变体。使用 Xcode 12.1.

进行测试

    NotificationCenter.default.addObserver(observerA, 
       selector: #selector(ObserverClassA.receivedNotification(notification:)), 
       name: Notification.Name("CustomNotification"), 
       object: nil)   // << subscribe for all

    let notificationToPost = Notification(name: Notification.Name("CustomNotification"), object: "This is the message", userInfo: nil)
    NotificationCenter.default.post(notificationToPost)

为什么我无法在 SwiftUI 的视图结构内收到有关观察者 class 的通知？

Why I can't receive a notification on an observer class inside a View struct in SwiftUI?

swift

swiftui

nsnotificationcenter