如何更新视图状态以响应外部更改？

Question

假设我有一个具有某些可变状态的视图，但可能需要更新该状态以反映另一个对象（例如 ViewModel）中的更改。

如何在 SwiftUI 中实现它？

我尝试了以下方法，但无法获得反映来自 ViewModel:

的更新的视图

class ViewModel: ObservableObject {

    @Published var text: String = "loading"

    private var task: AnyCancellable?

    func fetch() {
        task = Just("done")
            .delay(for: 1, scheduler: RunLoop.main)
            .assign(to: \.text, on: self)
    }
}

struct ContentView: View {

    @ObservedObject var viewModel = ViewModel()

    @State var viewText = "idle"

    private var bind: AnyCancellable?

    init() {
        viewText = viewModel.text
        bind = viewModel
            .$text
            .print()
            .assign(to: \.viewText, on: self)
    }

    var body: some View {
        VStack {
            TextField(titleKey: "editable text", text: $viewText)
            Text(viewText)
            Text(viewModel.text)
        }
        .onAppear {
            self.viewModel.fetch()
        }
    }
}

TextField 和第一个 Text 元素从 ContentView.viewText 获取内容，第二个 Text 直接转到源：ViewModel.text.

正如预期的那样，第二个 Text 显示 "loading"，然后是 "done"。第一个 Text 永远不会从 "idle" 改变。

Answer 1

这是可能的方法（测试并适用于 Xcode 11.2 / iOS 13.2）- 仅修改 ContentView:

struct ContentView: View {

    @ObservedObject var viewModel = ViewModelX()
    @State private var viewText = "idle"

    init() {
        _viewText = State<String>(initialValue: viewModel.text)
    }

    var body: some View {
        VStack {
            Text(viewText)
            Text(viewModel.text)
        }
        .onReceive(viewModel.$text) { value in
            self.viewText = value
        }
        .onAppear {
            self.viewModel.fetch()
        }
    }
}

Answer 2

如果下一个屏幕录制看起来像是在回答您的问题

它是使用下一个代码记录的

import SwiftUI
import Combine

class ViewModel: ObservableObject {

    @Published var text: String = "loading"

    private var task: AnyCancellable?

    func fetch() {
        task = Just("done")
            .delay(for: 3, scheduler: RunLoop.main)
            .assign(to: \.text, on: self)
    }
}

struct ContentView: View {

    @ObservedObject var viewModel = ViewModel()
    @State var viewText = "idle"

    var body: some View {
        VStack {
            Text(viewText)
            Text(viewModel.text)
        }.onReceive(viewModel.$text.filter({ (s) -> Bool in
            s == "done"
        })) { (txt) in
                self.viewText = txt
        }.onAppear {
            self.viewModel.fetch()
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

如何更新视图状态以响应外部更改？

How can I update view state in response to external changes?

swift

swiftui

combine