删除视图中的绑定对象时出现“致命错误：索引超出范围”

Question

在修改子视图依赖于绑定对象的数组时，我在避免索引超出范围错误时遇到了一些麻烦。

我有一个名为 WorkoutList 的父视图。 WorkoutList 有一个 ActiveWorkoutStore 的 EnvironmentObject。 ActiveWorkoutStore 是一个 ObservableObject，它有一个 Workout 对象数组。我有一个从 ActiveWorkoutStore 中检索到的活动锻炼列表。我正在使用 ForEach 循环来处理这些活动锻炼的索引，并将对象绑定传递给名为 EditWorkout 的子视图作为 NavigationLink 的目标。 EditWorkout 有一个完成锻炼的按钮，该按钮将其从 ActiveWorkoutStore 的锻炼数组中删除并将其添加到 WorkoutHistoryStore。当我从 ActiveWorkoutStore 的 activeWorkouts 数组中删除这个对象时，我遇到了麻烦，立即导致索引超出范围错误。我怀疑这是因为活动视图依赖于我刚刚删除的绑定对象。我已经尝试了几种排列方式，包括将锻炼传递给 EditWorkout，然后使用它的 id 来引用 ActiveWorkoutStore 中的锻炼来执行我的操作，但遇到了类似的麻烦。我在网上看到了很多遵循这种利用 ForEach 迭代索引的模式的示例，并且我已经尽我所能地对其进行了镜像，但我怀疑我可能遗漏了该方法的细微差别。

我在下面附上了代码示例。让我知道您是否有任何问题或是否还有其他我应该包括的内容！提前感谢您的帮助！

锻炼列表（父视图）

import SwiftUI

struct WorkoutList: View {
    @EnvironmentObject var activeWorkoutsStore: ActiveWorkoutStore
    @State private var addExercise = false
    @State private var workoutInProgress = false

    var newWorkoutButton: some View {
        Button(action: {
            self.activeWorkoutsStore.newActiveWorkout()
        }) {
            Text("New Workout")
            Image(systemName: "plus.circle")
        }
    }

    var body: some View {
        NavigationView {
            Group {
                if activeWorkoutsStore.activeWorkouts.isEmpty {
                    Text("No active workouts")
                } else {
                    List {
                        ForEach(activeWorkoutsStore.activeWorkouts.indices.reversed(), id: \.self) { activeWorkoutIndex in
                            NavigationLink(destination: EditWorkout(activeWorkout: self.$activeWorkoutsStore.activeWorkouts[activeWorkoutIndex])) {
                                Text(self.activeWorkoutsStore.activeWorkouts[activeWorkoutIndex].id.uuidString)
                            }
                        }
                    }
                }
            }
            .navigationBarTitle(Text("Active Workouts"))
            .navigationBarItems(trailing: newWorkoutButton)
        }
    }
}

EditWorkout（子视图）

//
//  EditWorkout.swift
//  workout-planner
//
//  Created by Dominic Minischetti III on 11/2/19.
//  Copyright © 2019 Dominic Minischetti. All rights reserved.
//

import SwiftUI

struct EditWorkout: View {
    @EnvironmentObject var workoutHistoryStore: WorkoutHistoryStore
    @EnvironmentObject var activeWorkoutStore: ActiveWorkoutStore
    @EnvironmentObject var exerciseStore: ExerciseStore
    @Environment(\.presentationMode) var presentationMode
    @State private var addExercise = false
    @Binding var activeWorkout: Workout
    
    var currentDayOfWeek: String {
        let weekdayIndex = Calendar.current.component(.weekday, from: Date())
        return Calendar.current.weekdaySymbols[weekdayIndex - 1]
    }

    var chooseExercisesButton: some View {
        Button (action: {
            self.addExercise = true
        }) {
            HStack {
                Image(systemName: "plus.square")
                Text("Choose Exercises")
            }
        }
        .sheet(isPresented: self.$addExercise) {
            AddWorkoutExercise(exercises: self.$activeWorkout.exercises)
                .environmentObject(self.exerciseStore)

        }
    }
    
    var saveButton: some View {
        Button(action: {
            self.workoutHistoryStore.addWorkout(workout: self.$activeWorkout.wrappedValue)
            self.activeWorkoutStore.removeActiveWorkout(workout: self.$activeWorkout.wrappedValue)
            self.presentationMode.wrappedValue.dismiss()
        }) {
            Text("Finish Workout")
        }
        .disabled(self.$activeWorkout.wrappedValue.exercises.isEmpty)
    }

    var body: some View {
        Form {
            Section(footer: Text("Choose which exercises are part of this workout")) {
                chooseExercisesButton
            }
            Section(header: Text("Exercises")) {
                if $activeWorkout.wrappedValue.exercises.isEmpty {
                    Text("No exercises")
                } else {
                    ForEach(activeWorkout.exercises.indices, id: \.self) { exerciseIndex in
                        NavigationLink(destination: EditWorkoutExercise(exercise: self.$activeWorkout.exercises[exerciseIndex])) {
                            VStack(alignment: .leading) {
                                Text(self.activeWorkout.exercises[exerciseIndex].name)
                                Text("\(self.activeWorkout.exercises[exerciseIndex].sets.count) Set\(self.activeWorkout.exercises[exerciseIndex].sets.count == 1 ? "" : "s")")
                                    .font(.footnote)
                                    .opacity(0.5)
                            }
                        }
                    }
                    saveButton
                }
            }
        }
        .navigationBarTitle(Text("Edit Workout"), displayMode: .inline )
    }
}

ActiveWorkoutStore

import Foundation
import Combine

class ActiveWorkoutStore: ObservableObject {
    @Published var activeWorkouts: [Workout] = []
    
    func newActiveWorkout() {
        activeWorkouts.append(Workout())
    }
    
    func saveActiveWorkout(workout: Workout) {
        let workoutIndex = activeWorkouts.firstIndex(where: { $0.id == workout.id })!
        
        activeWorkouts[workoutIndex] = workout
    }
    
    func removeActiveWorkout(workout: Workout) {
        if let workoutIndex = activeWorkouts.firstIndex(where: { $0.id == workout.id }) {
            activeWorkouts.remove(at: workoutIndex)
        }
    }
}

锻炼

import SwiftUI

struct Workout: Hashable, Codable, Identifiable {
    var id = UUID()
    var date = Date()
    var exercises: [WorkoutExercise] = []
}

Answer 1

ForEach<Range>是常量范围容器（注意下面构造函数的描述），构造后不允许修改。

extension ForEach where Data == Range<Int>, ID == Int, Content : View {

    /// Creates an instance that computes views on demand over a *constant*
    /// range.
    ///
    /// This instance only reads the initial value of `data` and so it does not
    /// need to identify views across updates.
    ///
    /// To compute views on demand over a dynamic range use
    /// `ForEach(_:id:content:)`.
    public init(_ data: Range<Int>, @ViewBuilder content: @escaping (Int) -> Content)
}

如果要修改容器，必须使用ForEach(activeWorkout.exercises)