ListBox SelectedItems Binding

Question

I want to bind Listbox selectedItems to array. But .NET throw exceprion in runtime.

            d.SetBinding(ListBox.SelectedItemsProperty, new Binding { Source = SomeArray });

Where "d" some ListBox from XAML.

Exception: Selected Item cannot be bound. Why?

Answer 1

ListBox.SelectedItems is read-only. Did you mean to bind to ListBox.SelectedItem instead?

Answer 2

Hi Polaris...

I am not sure if I understand your question correctly or the exact scenario - but assuming you wanted to have one listbox "d" show the items that were selected in another listbox "MyOtherListbox" then you just need to set the binding mode to 'one way' else it will bring up an error.

You could do something like

d.SetBinding(ListBox.ItemsSourceProperty, new Binding { Source = MyOtherListbox.SelectedItems, Mode = BindingMode.OneWay});

Answer 3

You can subscribe to the SelectionChanged event of the ListBox, and in the handler sync a collection of selected items.

In this example the Windows DataContext was set to itself (this) in its constructor. You could also easily call into a logic layer (ViewModel if you're using MVVM) from the event handler.

In Xaml:

<StackPanel>

    <ListBox
        ItemsSource="{Binding ListBoxItems}"
        SelectionMode="Multiple"
        SelectionChanged="ListBox_SelectionChanged">
    </ListBox>

    <ItemsControl
        ItemsSource="{Binding SelectedItems}">
    </ItemsControl>

</StackPanel>

And in the code-behind:

private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    foreach (string item in e.RemovedItems)
    {
        SelectedItems.Remove(item);
    }

    foreach (string item in e.AddedItems)
    {
        SelectedItems.Add(item);
    }
}

Answer 4

Mark Pearl comment help me undesrtand this issue. I just need listbox.selectedItmes.add method. Thank everybody for help.

Answer 5

This is the working solution, however when selection changes SelectedItemsProperty does not refresh bindings...

you can create a custom control as follow

public class MyListBox: ListBox{

    public MyListBox()
    { 
         this.SelectionChanged += (s,e)=>{ RefreshBindings(); };
    }

    private void RefreshBindings()
    {
         BindingExpression be = 
             (BindingExpression) GetBindingExpression(
                                      SelectedItemsProperty);
         if(be!=null){
               bd.UpdateTarget();
         }
    }

}

or in your app you can define event in every listbox as shown below ..

myListBox.SelectionChanged += (s,e) => {
    BindingExpression be = 
         (BindingExpression) myListBox.GetBindingExpression(
                                      ListBox.SelectedItemsProperty);
    if(be!=null){
        bd.UpdateTarget();
    }
};