Binding doesn't show ObservableCollection

Why is my listview, empty, while ‘Klanten’ has objects?
I have removed the toString in the object class also.

c# constructor

    public partial class Klantbeheerder: Window {
        public ObservableCollection < Klant > Klanten;
        private KlantManager _manager;
        public Klantbeheerder() {
          InitializeComponent();
          _manager = new(new KlantRepo(ConfigurationManager.ConnectionStrings["connStr"].ToString()));
          Klanten = _manager.GeefKlanten();
          DataContext = Klanten;
        }

Window

    d:DataContext="{d:DesignInstance local:Klantbeheerder, IsDesignTimeCreatable=True}"

Inside Grid

<ListView
   x:Name="lstvKlanten"
   Height="270"
   Margin="0,15,15,15"
   HorizontalAlignment="Left"
   ItemsSource="{Binding Klanten}"
   SelectionMode="Single">
   <ListView.View>
      <GridView>
         <GridViewColumn
            Width="50"
            DisplayMemberBinding="{Binding Id}"
            Header="Id" />
         <GridViewColumn
            Width="150"
            DisplayMemberBinding="{Binding Naam}"
            Header="Naam" />
         <GridViewColumn
            Width="100"
            DisplayMemberBinding="{Binding Adres}"
            Header="Adres" />
      </GridView>
   </ListView.View>
</ListView>

>Solution :

Why you use ListView for translate grid? Use DataGrid, it’s simple:

MainWindow.xaml:

<DataGrid ItemsSource="{Binding Products}" AutoGenerateColumns="False">
   <DataGrid.Columns>
      <DataGridTextColumn Header="Product"  Binding="{Binding Name}" />
      <DataGridTextColumn Header="Price" Binding="{Binding Price}" />
   </DataGrid.Columns>
</DataGrid>

MainWindow.xaml.cs:

//LOOK, THIS IS PROPERTY!!
public ObservableCollection<Product> Products { get; set; }
public MainWindow()
{
    InitializeComponent();
    Products = new ObservableCollection<Product>();
    Products.Add(new Product { Name = "Apple", Price = 1 });
    Products.Add(new Product { Name = "Banana", Price = 2 });

    DataContext = this;
}