尝试在ZStack中实现NavigationView时，为什么我的应用程序崩溃？

Question

所以由于某种原因，当我尝试在ZStack中实现NavigationView时，我的应用程序崩溃了。

当我按下按钮时，我试图显示一个弹出窗口。不幸的是，它不起作用。

这是我的代码：

//  gymappswiftuivone
//
//  Created by Yonatan Bensimon on 2019-12-29.
//  Copyright © 2019 Yonatan Bensimon. All rights reserved.
//

import SwiftUI
import Combine

struct Log: View {

        @Environment(\.managedObjectContext) var managedObjectContext //The Context
        @FetchRequest(fetchRequest: ExerciseForWorkout.getAllExerciseForWorkout()) var loggedExercise: FetchedResults < ExerciseForWorkout > //The request in memory
            @EnvironmentObject
        var userData: UserData

        @State var newLoggedExercise = ""
        @State private var newReps: String = ""
        @State private var newWeight: String = ""

        @State private var isAppeared: Bool = false

        @State var float: CGFloat = 20.0

        var body: some View {
              ZStack {
                    VStack {
                        NavigationView { //ERROR
                            List {
                                Section(header: Text("Add Exercise")) {
                                        HStack {
                                            TextField("Exercise", text: $newLoggedExercise)
                                                .disabled(true)
                                                .onTapGesture {
                                                    self.isAppeared = true
                                                }
                                            TextField("Weight", text: $newWeight)
                                                .keyboardType(.numberPad)
                                                .onReceive(Just(newWeight)) {
                                                    newValue in
                                                        let filtered = newValue.filter {
                                                            "0123456789".contains($0)
                                                        }
                                                    if filtered != newValue {
                                                        self.newWeight = filtered
                                                    }
                                                }
                                            TextField("Reps", text: $newReps)
                                                .keyboardType(.numberPad)
                                                .onReceive(Just(newReps)) {
                                                    newValue in
                                                        let filtered2 = newValue.filter {
                                                            "0123456789".contains($0)
                                                        }
                                                    if filtered2 != newValue {
                                                        self.newReps = filtered2
                                                    }
                                                }
                                            Button(action: {
                                                let loggedExerciseNew = ExerciseForWorkout(context: self.managedObjectContext)
                                                loggedExerciseNew.name = self.newLoggedExercise
                                                loggedExerciseNew.reps = self.newReps
                                                loggedExerciseNew.dateCreated = Date()
                                                loggedExerciseNew.weight = self.newWeight

                                                do {
                                                    try self.managedObjectContext.save()
                                                } catch {
                                                    print("Error while saving !!!")
                                                    print(error)
                                                }

                                                self.newLoggedExercise = ""

                                            }) {
                                                Image(systemName: "plus.circle.fill")
                                                    .foregroundColor(Color.green)
                                                    .imageScale(.large)
                                            }
                                        }
                                    } //Sectio

                                Section(header: sectionHeader()) {
                                    ForEach(self.loggedExercise, id: \.self) {
                                        log in
                                            loggedExerciseTab(name: log.name, reps: log.reps, weight: log.weight)
                                    }.onDelete {
                                        indexSet in
                                            let deleteEx = self.loggedExercise[indexSet.first!]
                                        self.managedObjectContext.delete(deleteEx)

                                        do {
                                            try self.managedObjectContext.save()
                                        } catch {
                                            print("Error while saving !!!")
                                            print(error)
                                        }
                                    }
                                }
                            } //List
                            .navigationBarTitle(Text("Log"))
                                .navigationBarItems(trailing: EditButton())
                        } //Navigation View

                        Button(action: {}) {
                            completeWorkout()
                                .padding()
                        }

                }
                    //ZSTACK

                    if $isAppeared.wrappedValue {
                            ZStack {
                                Color.black.opacity(0.4)
                                    .edgesIgnoringSafeArea(.vertical)
                                VStack(spacing: 20) {
                                        Text("Choose Exercise")
                                            .bold().padding()
                                            .frame(maxWidth: .infinity)
                                            .background(Color.blue)
                                            .foregroundColor(Color.white)
                                        Spacer()
                                        Button(action: {
                                            self.isAppeared = false
                                        }) {
                                            Picker(selection: $newLoggedExercise) {
                                                ForEach(0... < exerciseData.count) {
                                                    Text(exerciseData[$0].name).tag(exerciseData)
                                                }
                                            }
                                        }.padding()
                                    }
                                    .frame(width: CGFloat(300), height: CGFloat(200))
                                    .background(Color.white)
                                    .cornerRadius(float).shadow(radius: float)
                            }
                        } //IF

                } //ZStack Doe

            } //BODY
    } //VIEW

struct Log_Previews: PreviewProvider {
    static
    var previews: some View {
        Log()
    }
}

当我声明NavigationView时，Xcode给我这个错误：

Generic parameter 'Content' could not be inferred Explicitly specify the generic arguments to fix this issue

我已经尝试了一切，但仍然想不通！ 谁能找到我的错误/错误，如果找不到，您对我应该如何实现弹出窗口有更好的想法？