Drag and Drop within ListBox with databound SelectedItem causes null set

[Steve]

Hello,

I am trying to get Drag and Drop to work within a single RadListBox.  I have the ItemsSource and SelectedItem bound (TwoWay).  Whenever I drop an item within the listbox, the SelectedItem setter gets called with a value of null.  I was able to reproduce this by updating the SDK sample "CustomListBoxDragDropBehavior_WPF" with the following:

<telerik:RadListBox ItemContainerStyle="{StaticResource DraggableListBoxItem}"
                            ItemsSource="{Binding Customers1}"
                            SelectedItem="{Binding SelectedCustomer1, Mode=TwoWay}"

private Customer selectedCustomer1;
        public Customer SelectedCustomer1
        {
            get { return selectedCustomer1; }
            set
            {
                selectedCustomer1 = value;
                this.OnPropertyChanged(() => this.SelectedCustomer1);
            }
        }

How do I prevent the selected item to be called with null?

Thanks,
Steve

[Kalin]

Hi Steve,

The SelectedItem is being set to null because of the ListBox DradDragBehavior implementation. Whenever the dragged ListItem is dropped it has been removed from the ItemsSource of the first ListBox and added to the ItemsSource of the second ListBox. So in order to achieve the desired scenario in a single ListBox I would suggest a quick solution. Just use our CustomListBoxDragDropBehavior SDK example as a base and add the code snippet below:

public MainWindow()
{
    InitializeComponent();
    DragDropManager.AddDropHandler(this.lb1, OnDrop, true);
}

private void OnDrop(object sender, Telerik.Windows.DragDrop.DragEventArgs e)
{
    var data = ((DataObject)e.Data).GetData(typeof(Customer));
    this.lb1.SelectedItem = ((IList)data)[0];
}

This will extend the Drop handler of the DragDropManager in order to set the dropped ListItem as the SelectedItem (you would only need to set the name of the first ListBox to "lb1").

Hope this helps.

Regards,
Kalin
Telerik