SwiftUI 【After writing a good run, the final simulator program only shows Goodone. Swift, a single module. The ContentView.swift content cannot be displayed. Unable to use the program properly. Need help】

After writing a good run, the final simulator program only shows Goodone. Swift, a single module. The ContentView.swift content cannot be displayed. Unable to use the program properly. Need help

// goodone.swift
// 
//
// Created by user on 2021/6/4.
//

import SwiftUI

struct goodone: View {
   
  let coreDM: CoreDataManager
  @State private var movieTitle: String = ""
   
  @State private var movies: [Movie] = [Movie]()
  @State private var needsRefresh: Bool = false
  private func populateMovies(){
    movies = coreDM.getAllMovie()
     
  }
  var body: some View {
    NavigationView{
       
      VStack {
        TextField("输入待办事项", text: $movieTitle)
          .textFieldStyle(RoundedBorderTextFieldStyle())
        Button("保存"){
          coreDM.saveMovie(title: movieTitle)
          populateMovies()
        }
         
        List {
        
          ForEach(movies, id:\.self) { movie in
             
            NavigationLink(
              destination: MovieDetail(movie: movie, coreDM: coreDM, needsRefresh: $needsRefresh),
              label: {
                Text(movie.title ?? "")
              })
             
          }.onDelete(perform: { indexSet in
            indexSet.forEach{ index in
              let movie = movies[index]
              //delete it using Core Data Manager
              coreDM.deleteMovie(movie: movie)
              populateMovies()
               
            }
            
          })
           
        }.listStyle(PlainListStyle())
        .accentColor(needsRefresh ?.white:.black)
         
         
        Spacer()
        }.padding()
      .navigationTitle("待办事项")
       
      .onAppear(perform: {
        populateMovies()
      })
      }
    }
  }
struct goodone_Previews: PreviewProvider {
  static var previews: some View {
     
    goodone(coreDM: CoreDataManager())
  }
}

// Main.swift
// 
//
// Created by user on 2021/5/27.
//

import SwiftUI

struct Main: View {
  var body: some View {
    TabView{
      goodone(coreDM: CoreDataManager())
        .tabItem {
          Image(systemName: "bolt.car")
          Text("待办事项")
        }.tag(1)
      Text("车主信息")
        .tabItem {
          Image(systemName: "car.fill")
          Text("车主信息")
        }.tag(2)
      Text("车主需求")
        .tabItem {
          Image(systemName: "person")
          Text("车主需求")
        }.tag(3)
      Text("信息检索")
        .tabItem {
          Image(systemName: "simcard.2")
          Text("信息检索")
        }.tag(4)
    }.accentColor(.red)
    .font(.title3)
  }
}

struct Main_Previews: PreviewProvider {
  static var previews: some View {
    
    Main()
  }
}


// ContentView.swift
// 
//
// Created by user on 2021/5/27.
//

import SwiftUI

struct ContentView: View {
   
   
  var body: some View {
     
    Main()
     
     
  }


struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}
}

I wrote a separate agent module and it works fine. The combination is normal. It's normal in Xcode. Run the program to the simulator, or the real machine. There is only one agent module. The entire program cannot be displayed.

SwiftUI 【After writing a good run, the final simulator program only shows Goodone. Swift, a single module. The ContentView.swift content cannot be displayed. Unable to use the program properly. Need help】
 
 
Q