SwiftUI：如何在父视图中初始化一个新的 StateObject？

Question

我有一个类似于以下（简化）代码的应用程序架构。 我使用在设置视图中初始化的WorkoutManager StateObject ，然后通过EnvironmentObject传递给它的子项。 问题是，在解除.sheet ，没有任何生命周期事件会初始化一个新的WorkoutManager ，我需要它才能连续开始新的锻炼。 在下面的这个例子中，我如何让WorkoutView能够重新初始化 WorkoutManager 使其成为一个干净的对象？

import SwiftUI
import HealthKit

class WorkoutManager: ObservableObject {
    
    var workout: HKWorkout?
}

struct ContentView: View {
    
    @StateObject var workoutManager = WorkoutManager()
    
    @State var showingWorkoutView = false
    
    var body: some View {
      
        Button {
            showingWorkoutView.toggle()
        } label: {
            Text("Start Workout")
        }
        .sheet(isPresented: $showingWorkoutView) {
            WorkoutView(showingWorkoutView: $showingWorkoutView)
        }
        
    }
}

struct WorkoutView: View {
    
    @EnvironmentObject var workoutManager:  WorkoutManager
    @Binding var showingWorkoutView: Bool
    
    var body: some View {
        Text("Workout Started")
            .padding()
        Button {
            showingWorkoutView.toggle()
            //Here I want to initialize a new WorkoutManager to clear out the previous workout's state, how? 
        } label: {
            Text("End Workout")
        }

    }
}

Answer 1

正如评论中已经提到的，您可能想要采取的路线是在同一个WorkoutManager状态。 无论如何，您都无法将新对象分配给@StateObject - 由于View的不可变self最终会出现编译器错误。

其次，我建议您可能不想依赖WorkoutView的Button来执行此操作。 例如，如果用户通过滑动关闭工作sheet ，则不会调用。 相反，您可以在onChange监听sheet的状态（另一种方法是使用sheet的onDismiss参数）：

class WorkoutManager: ObservableObject {
    var workout: HKWorkout?
    
    func resetState() {
        //do whatever you need to do to reset the state
        print("Reset state")
    }
}

struct ContentView: View {
    
    @StateObject var workoutManager = WorkoutManager()
    
    @State var showingWorkoutView = false
    
    var body: some View {
      
        Button {
            showingWorkoutView.toggle()
        } label: {
            Text("Start Workout")
        }
        .sheet(isPresented: $showingWorkoutView) {
            WorkoutView(showingWorkoutView: $showingWorkoutView)
        }
        .onChange(of: showingWorkoutView) { newValue in
            if !newValue {
                workoutManager.resetState()
            }
        }
    }
}

struct WorkoutView: View {
    
    @EnvironmentObject var workoutManager:  WorkoutManager
    @Binding var showingWorkoutView: Bool
    
    var body: some View {
        Text("Workout Started")
            .padding()
        Button {
            showingWorkoutView.toggle()
        } label: {
            Text("End Workout")
        }

    }
}