SwiftUI：如何在父視圖中初始化一個新的 StateObject？

Question

我有一個類似於以下（簡化）代碼的應用程序架構。 我使用在設置視圖中初始化的WorkoutManager StateObject ，然后通過EnvironmentObject傳遞給它的子項。 問題是，在解除.sheet ，沒有任何生命周期事件會初始化一個新的WorkoutManager ，我需要它才能連續開始新的鍛煉。 在下面的這個例子中，我如何讓WorkoutView能夠重新初始化 WorkoutManager 使其成為一個干凈的對象？

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

正如評論中已經提到的，您可能想要采取的路線是在同一個WorkoutManager狀態。 無論如何，您都無法將新對象分配給@StateObject - 由於View的不可變self最終會出現編譯器錯誤。

其次，我建議您可能不想依賴WorkoutView的Button來執行此操作。 例如，如果用戶通過滑動關閉工作sheet ，則不會調用。 相反，您可以在onChange監聽sheet的狀態（另一種方法是使用sheet的onDismiss參數）：

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")
        }

    }
}