SwiftUI：视图模型内部发布的字符串更改不会更新视图

Question

我在视图模型类中有一个计时器，该计时器每秒钟更改视图模型中的两个@Published字符串。视图模型类是一个可观察的对象，可被视图观察，但是对这些字符串对象的更改不会更新我的视图。

我在许多其他视图中具有非常相似的结构（在ObservableObject内的已发布变量由视图观察），并且始终有效。我似乎找不到我在做什么错？

ViewModel

final class QWMeasurementViewModel: ObservableObject {

    @Published var measurementCountDownDetails: String = ""
    @Published var measurementCountDown: String = ""

    private var timer: Timer?
    private var scheduleTime = 0

    func setTimer() {
        timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in
            DispatchQueue.main.async {
                self.scheduleTime += 1
                if self.scheduleTime == 1 {
                    self.measurementCountDownDetails = "Get ready"
                    self.measurementCountDown = "1"
                }
                else if self.scheduleTime == 2 {
                    self.measurementCountDownDetails = "Relax your arm"
                    self.measurementCountDown = "2"
                }
                else if self.scheduleTime == 3 {
                    self.measurementCountDownDetails = "Breathe"
                    self.measurementCountDown = "3"
                }
                else if self.scheduleTime == 4 {
                    self.measurementCountDownDetails = ""
                    self.measurementCountDown = ""
                    timer.invalidate()
                }
            }
        }
    }
}

查看

struct QWMeasurementView: View {
    @ObservedObject var viewModel: QWMeasurementViewModel

    var body: some View {
        VStack {
            Text(viewModel.measurementCountDownDetails)
                .font(.body)
            Text(viewModel.measurementCountDown)
                .font(.title)
        }
        .onAppear {
            viewModel.setTimer()
        }
    }
}

编辑

经过调查，这似乎与它的呈现方式有关。因为如果是单一视图，则此代码有效，但实际上是作为表格展示的。 （仍然无法理解为什么会有所作为。）

struct QWBPDStartButtonView: View {

    @ObservedObject private var viewModel: QWBPDStartButtonViewModel
    @State private var startButtonPressed: Bool = false

    init(viewModel: QWBPDStartButtonViewModel) {
        self.viewModel = viewModel
    }

    var body: some View {
        Button(action: {
            self.startButtonPressed = true
        }) {
            ZStack {
                Circle()
                    .foregroundColor(Color("midGreen"))
                Text("Start")
                    .font(.title)
            }
        }
        .buttonStyle(PlainButtonStyle())
        .sheet(isPresented: $startButtonPressed) {
            QWMeasurementView(viewModel: QWMeasurementViewModel())
        }
    }
}

Answer 1

您正在将全新的视图模型传递到工作表视图。 尝试从第3行传入实例