将 Listbox 的 Itemsource 绑定到 Code behind 中的方法

Question

I have a Database and a XAML File an in there I have two Listboxes, the first one ( lbAg ) to list the topics ( ag_name , like finances, HR, etc.) and the second one ( liAn ) to list the tasks in that field which have to be done ( an_anligen , like paying the accountant etc..). The thing is, I want the Items of liAn to be the tasks of the selected Item from liAg , but only if the attribute an_fertig (an_done) to be false. This I want to achieve by binding it to a method in the code behind.

Please help, Thanks in advance. XAML:

<ListBox Grid.Column="0" 
         Grid.RowSpan="2"
         x:Name="liAg" 
         Loaded="liAg_Loaded" 
         DisplayMemberPath="ag_name"  />

<ListBox Grid.Column="1" 
         Grid.RowSpan="2"
         x:Name="liAn"  
          ItemsSource="{Binding liAn_Items}"
         DisplayMemberPath="an_titel" />

Code-behind:

public partial class Main : UserControl
{
    public Main()
    {
        InitializeComponent();
    }

    DbEntities db = new DbEntities();

    private void liAg_Loaded(object sender, RoutedEventArgs e)
    {
        liAg.ItemsSource = db.ag_arbeitsgemeinschaft.ToList();
    }

    private void liAn_Items(object sender, RoutedEventArgs e)
    {
        string liag = liAg.SelectedItem.ToString();
        Console.WriteLine(liag);

        var erg = from a in db.an_anliegen
            where a.an_ag == liag && a.an_fertig != true
            select a;

        liAn.ItemsSource = erg.ToList();
    }
}

Answer 1

If you really want to bind to a method, you can use the ObjectDataProvider : Microsoft Docs: How to: Bind to a Method .

You have many options. You can make use of the ListBox.SelectionChanged event to trigger the database query.

I highly recommend not to mix XAML data binding and direct property assignment using C#. You should use data binding when possible.

I have created some DependencyProperty data source properties for the ListBox.ItemsSource properties to bind to. Since you didn't supplied any details about your data item type, I bound the ListBox to a collection of the fictional DataItem type:

MainWindow.xaml.cs

partial class MainWindow : Window
{
  public static readonly DependencyProperty DataItemsProperty = DependencyProperty.Register(
    "DataItems",
    typeof(IEnumerable),
    typeof(MainWindow),
    new PropertyMetadata(default(IEnumerable)));

  public IEnumerable DataItems
  {
    get => (IEnumerable) GetValue(MainWindow.DataItemsProperty);
    set => SetValue(MainWindow.DataItemsProperty, value);
  }

  public static readonly DependencyProperty TasksProperty = DependencyProperty.Register(
    "Tasks",
    typeof(IEnumerable),
    typeof(MainWindow),
    new PropertyMetadata(default(IEnumerable)));

  public IEnumerable Tasks
  {
    get => (IEnumerable) GetValue(MainWindow.TasksProperty);
    set => SetValue(MainWindow.TasksProperty, value);
  }

  public MainWindow()
  {
    this.DataItems = db.ag_arbeitsgemeinschaft.ToList();
  }

  private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
  {
    // Cast the ListBox.SelectedItem from object to the data type
    DataItem selectedItem = e.AddedItems.OfType<DataItem>().FirstOrDefault();
    if (selectedItem == null)
    {
      return;
    }

    // Access the selected item's members
    string displayedValue = selectedItem.ag_name;

    // Execute query
    var erg = from a in db.an_anliegen
            where a.an_ag == displayedValue && !a.an_fertig
            select a;

    // Update binding source of the ListBox named 'liAn'
    this.Tasks = erg.ToList();
  }
}

MainWindow.xaml

<Window>
  <ListBox x:Name="liAg" 
           ItemsSource="{Binding RelativeSource={RelativeSource AncestorType=MainWindow}, 
                         Path=DataItems}"
           DisplayMemberPath="ag_name"
           SelectionChanged="OnSelectionChanged" />

  <ListBox x:Name="liAn"  
           ItemsSource="{Binding RelativeSource={RelativeSource AncestorType=MainWindow}, 
                         Path=Tasks}"
           DisplayMemberPath="an_titel" />
</Window>