SelectedItemsSource

With the Q1 2015 release version of UI for WPF, the ability to manipulate the SelectedItems collection of RadListBox through the ViewModel is now available. This is now possible with the brand new ListBoxSelectedItemsBehavior behavior and its SelectedItemsSource attached property. The SelectedItemsSource is a collection that synchronizes itself with the SelectedItems collection of RadListBox – thus if an item is added, removed or the collection is replaced/cleared those actions will be executed on the SelectedItems collection as well.

Using the SelectedItemsSource

The following example will demonstrate how to bind the SelectedItemsSource property of the ListBoxSelectedItemsBehavior to a collection of custom objects. In order the synchronization between the SelectedItemSource and the SelectedItems of RadListBox control to be possible the bound collection should implement both the IEnumerable and the INotifyCollectionChanged interfaces.

Synchronization won’t be possible if SelectedItemsSource is bound to a collection that does not implement INotifyCollectionChanged.

First, you need to create a new business object named for example Item. Its structure is shown in the code-snippet below:

Business object Item

C#

	public class Item
	{
		public Item(string name)
		{
			this.Name = name;
		}
		public string Name { get; set; }
	}

VB

	Public Class Item
	    Public Sub New(ByVal name As String)
	        Me.Name = name
	    End Sub
	    Public Property Name() As String
	End Class

Next thing you have to do is to create a new class named ViewModel that inherits the Telerik ViewModelBase abstract class – inside it initialize two collections with sample data. The first one will be for the ItemsSource of RadListBox while the second one will be the data source for the SelectedItemsSource property:

Creating the ViewModel

C#

	private ObservableCollection<Item> items;
	private ObservableCollection<Item> selectedItemsSource;
	public ViewModel()
	{
		this.Items = this.GetItems(100);
		this.SelectedItemsSource = new ObservableCollection<Item>() { this.Items[0], this.Items[2], this.Items[4], this.Items[6], this.Items[7] }; 
	}
	public ObservableCollection<Item> SelectedItemsSource
	{
		get
		{
			return this.selectedItemsSource;
		}
		set
		{
			if (this.selectedItemsSource != value)
			{
				this.selectedItemsSource = value;
				this.OnPropertyChanged(() => this.SelectedItemsSource);
			}
		}
	}
	public ObservableCollection<Item> Items
	{
		get
		{
			return this.items;
		}
		set
		{
			if (this.items != value)
			{
				this.items = value;
				this.OnPropertyChanged(() => this.Items);
			}
		}
	}
	private ObservableCollection<Item> GetItems(int size)
	{
		var result = new ObservableCollection<Item>();
		for (int i = 0; i < size; i++)
		{
			result.Add(new Item(string.Format("Item {0}", i)));
		}
		return result;
	}

VB

	Private items_Renamed As ObservableCollection(Of Item)
	Private selectedItemsSource_Renamed As ObservableCollection(Of Item)
	Public Sub New()
	    Me.Items = Me.GetItems(100)
	    Me.SelectedItemsSource = New ObservableCollection(Of Item)() From {Me.Items(0), Me.Items(2), Me.Items(4), Me.Items(6), Me.Items(7)}
	End Sub
	Public Property SelectedItemsSource() As ObservableCollection(Of Item)
	    Get
	        Return Me.selectedItemsSource_Renamed
	    End Get
	    Set(ByVal value As ObservableCollection(Of Item))
	        If Me.selectedItemsSource_Renamed IsNot value Then
	            Me.selectedItemsSource_Renamed = value
	            Me.OnPropertyChanged(Function() Me.SelectedItemsSource)
	        End If
	    End Set
	End Property
	Public Property Items() As ObservableCollection(Of Item)
	    Get
	        Return Me.items_Renamed
	    End Get
	    Set(ByVal value As ObservableCollection(Of Item))
	        If Me.items_Renamed IsNot value Then
	            Me.items_Renamed = value
	            Me.OnPropertyChanged(Function() Me.Items)
	        End If
	    End Set
	End Property
	Private Function GetItems(ByVal size As Integer) As ObservableCollection(Of Item)
	    Dim result = New ObservableCollection(Of Item)()
	    For i As Integer = 0 To size - 1
	        result.Add(New Item(String.Format("Item {0}", i)))
	    Next i
	    Return result
	End Function

The SelectedItemsSource and the ItemsSource should be bound to collections of the same type of items.

Next you should declare the ViewModel as DataContext in your XAML:

Set the ViewModel as DataContext

XAML

	>
	<UserControl.DataContext>
	    <local:ViewModel/>
	</UserControl.DataContext>

Finally, all you need to do is to set both created collection of items to the ItemsSource and ListBoxSelectedItemsBehavior. SelectedItemsSource:

Set the ItemsSource and SelectedItemsSource

XAML

	<telerik:RadListBox x:Name="radListBox" ItemsSource="{Binding Items}"
	                    DisplayMemberPath="Name"
	                    SelectionMode="Multiple"
	                    telerik:ListBoxSelectedItemsBehavior.SelectedItemsSource="{Binding SelectedItemsSource}"/>

The final result is shown on the snapshot below:

Find a runnable project of the previous example in the WPF Samples GitHub repository.

See Also

• Selection

• Binding to Object