ios - 单例中的@Published 属性在第一个事件之后不发出事件

Question

我在单例类中有一个 @Published 属性，它在 View 模型类中被观察到，它只收到第一个初始值，而不是之后。为什么？

查看

import SwiftUI

struct ContentView: View {

    @ObservedObject var viewModel = ContentViewModel(singletonService: SingletonService.shared)

    var body: some View {
        NavigationView {
            Form {
                Text("Hello World")
            }.navigationBarItems(trailing: Button("Increase Number", action: {
                SingletonService.shared.increaseNumber()
            }))
        }
    }
}

View 模型

import Combine

class ContentViewModel: ObservableObject {

    init(
        singletonService: SingletonService
    ) {
        let cencellable = singletonService.$number.sink(receiveValue: { print($0) })
        // Never called after the first time
    }

}

单例

import Combine

class SingletonService {

    static let shared = SingletonService()

    @Published var number = 0

    func increaseNumber() {
        number += 1
    }

}

Answer 1

订阅一直存在，直到订阅者还活着，但在这种情况下

let cencellable = singletonService.$number.sink(receiveValue: { print($0) 

订阅者被断章取义。应该是这样的

private var cancellables = Set<AnyCancellable>()

init(singletonService: SingletonService) {
     singletonService.$number
        .sink(receiveValue: { print($0) })
        .store(in: &cancellables)
}