How to combine ListBox and ComboBox?

Question

Why is the data not updated in the ComboBox after it is changed in the ListBox? (ListBox and ComboBox` are in different files) Оn the start window there is an empty combobox,

<ComboBox
    x:Name="cmbUser"
    ItemsSource="{Binding ElementName=usersList, Path=Text, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
    Margin="211,50,211,267"
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <StackPanel>
                <TextBlock Text="{Binding Name}" FontSize="16" />
                <TextBlock Text="{Binding Age}" FontSize="13" />
            </StackPanel>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>
ComboBox

  public partial class MainWindow : Window
    {

        ApplicationContext db = new ApplicationContext();
        
        public MainWindow()
        {
            InitializeComponent();
            Loaded += MainWindow_Loaded;
            
                Binding binding = new Binding();
                binding.ElementName = "usersList";
                binding.Path = new PropertyPath("Text"); 
                cmbFarm.SetBinding(ComboBox.TextProperty, binding); 

        }


        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            db.Database.EnsureCreated();
            db.Users.Load();
            DataContext = db.Users.Local.ToObservableCollection();
        }
        // Open
        private void Open_Click(object sender, RoutedEventArgs e)
        {
            Open Open = new Open(new User());
            if (Open.ShowDialog() == true)
            {
                User user= (User)this.Resources["cmbFarm"];
                user.Name = user.Name; // Меняем с Google на LG

                User User = Open.User;
                db.Users.Add(User);
                db.SaveChanges();
            }
        } 

when i click on "Открыть 1", opens window with listbox, in which I can delete change add entries, and when i change the record they are not saved in the combobox.

 <ListBox x:Name="usersList" ItemsSource="{Binding}" ButtonBase.Click="Edit_Click" Margin="0,0,50,0" >
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <TextBlock Text="{Binding Name, Mode=TwoWay}" FontSize="16" />
                        <TextBlock Text="{Binding Age,  Mode=TwoWay}" FontSize="13" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

public partial class Open : Window
    {
        public User User { get; private set; }

        ApplicationContext db = new ApplicationContext();
        public Open(User user)
        {
            InitializeComponent();

            Loaded += Open_Loaded;
            User = user;
            DataContext = User;

        }


        private void Open_Loaded(object sender, RoutedEventArgs e)
        {

            db.Database.EnsureCreated();
            db.Users.Load();
            DataContext = db.Users.Local.ToObservableCollection();

           
               
            
        }
        // добавление
        private void Add_Click(object sender, RoutedEventArgs e)
        {

            UserWindow UserWindow = new UserWindow(new User());
            if (UserWindow.ShowDialog() == true)
            {
                User User = UserWindow.User;
                db.Users.Add(User);
                db.SaveChanges();

                
            }
        }
        // Edit
        private void Edit_Click(object sender, RoutedEventArgs e)
        {

            User? user = usersList.SelectedItem as User;
            if (user is null) return;

            UserWindow UserWindow = new UserWindow(new User
            {
                id = user.id,
                Age = user.Age,
                Name = user.Name
            });

            if (UserWindow.ShowDialog() == true)
            {
                user = db.Users.Find(UserWindow.User.id);
                if (user != null)
                {
                    user.Age = UserWindow.User.Age;
                    user.Name = UserWindow.User.Name;
                    db.SaveChanges();
   
                }
            }
        }

        // Delete
        private void Delete_Click(object sender, RoutedEventArgs e)
        {

            User? user = usersList.SelectedItem as User;
            if (user is null) return;
            db.Users.Remove(user);
            db.SaveChanges();
          
        }

    }

when I place combobox and listbox in one .cs and .xaml file the data is instantly updated after changing the lisbox

  public class User : INotifyPropertyChanged
    {
        public int id { get; set; }
        public string? name { get; set; }
        public int age { get; set; }

       
        public string Name
        {
            get { return name; }
            set
            {
                name = value;
                OnPropertyChanged("Name");
            }
        }
        public int Age
        {
            get { return age; }
            set
            {
                age = value;
                OnPropertyChanged("Age");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] string prop = "")
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(prop));
        }

Answer 1

Hi,@Максимилиан Янулевич. For combining ListBox and ComboBox, you could refer to the following code. MainWindow.xaml:

<Grid>

        <ComboBox  x:Name="cmbUser"  ItemsSource="{Binding Users ,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"
    Margin="211,50,211,267">
            <ComboBox.ItemTemplate>
            <DataTemplate>
                <StackPanel>
                    <TextBlock Text="{Binding Name}" FontSize="16" />
                    <TextBlock Text="{Binding Age}" FontSize="13" />
                </StackPanel>
            </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
        <Button Content="Open" Click="Open_Click" Width="100" Height="50" Margin="650,0,0,320"/>
    </Grid>

MainWindow.xaml.cs:

  public partial class MainWindow : Window, INotifyPropertyChanged
    {
        Open open;
        public MainWindow()
        {
            InitializeComponent();
            DataContext= this;
        }
        private ObservableCollection<User> users = new ObservableCollection<User>();
        public ObservableCollection<User> Users
        {
            get { return users; }
            set
            {
                if (users != value)
                {
                    users = value;
                    OnPropertyChanged("Users");
                }
            }
        }
        private void Open_Click(object sender, RoutedEventArgs e)
        {
            open = new Open(new User());
            if (open.ShowDialog() == true)
            {
                open.db.Users.Load();
                Users = open.db.Users.Local.ToObservableCollection();
                cmbUser.Items.Refresh();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string name = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }
    public class ApplicationContext : DbContext
    {
        public DbSet<User> Users { get; set; }
        protected override void OnConfiguring(
            DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlite(
                "Data Source=uses.db");
            optionsBuilder.UseLazyLoadingProxies();
        }
    }

    public class User 
    {
        private int id { get; set; }
        private string? name { get; set; }
        private int age { get; set; }

        public int Id
        {
            get { return id; }
            set
            {
                id = value;
                OnPropertyChanged("Id");
            }
        }
        public string? Name
        {
            get { return name; }
            set
            {
                name = value;
                OnPropertyChanged("Name");
            }
        }
        public int Age
        {
            get { return age; }
            set
            {
                age = value;
                OnPropertyChanged("Age");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] string prop = "")
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(prop));
        }
    }

Open.xaml.cs:

  public partial class Open : Window
    {
        public User User { get; private set; }

        public ApplicationContext db { get;set; } = new ApplicationContext();
      
        public Open(User user )
        {
            InitializeComponent();

            Loaded += Open_Loaded ;
            User = user;
            DataContext = User;
        }

        private void Open_Loaded(object sender, RoutedEventArgs e)
        {
            db.Database.EnsureCreated();
            db.Users.Load();
            DataContext = db.Users.Local.ToObservableCollection();
        }
        
        private void Add_Click(object sender, RoutedEventArgs e)
        {

            UserWindow UserWindow = new UserWindow(new User());
            if (UserWindow.ShowDialog() == true)
            {
                User User = UserWindow.User;
                
                db.Users.Add(User);
                db.SaveChanges();
                DialogResult = true;
            }
        }
        private void Edit_Click(object sender, RoutedEventArgs e)
        {
            User? user = usersList.SelectedItem as User;
            if (user is null) return;

            UserWindow UserWindow = new UserWindow(new User
            {
                Id = user.Id,
                Age = user.Age,
                Name = user.Name
            });

            if (UserWindow.ShowDialog() == true)
            {
                user = db.Users.Find(UserWindow.User.Id);
                if (user != null)
                {
                    user.Age = UserWindow.User.Age;
                    user.Name = UserWindow.User.Name;
                    db.SaveChanges();

                }
            }
        }
        private void Delete_Click(object sender, RoutedEventArgs e)
        {

            User? user = usersList.SelectedItem as User;
            if (user is null) return;
            db.Users.Remove(user);
            db.SaveChanges();

        }


    }

The result:

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