<CategoryAttribute("Common Properties")>
Public Property IsSelected As Boolean

Dim instance As ISSelectionItemControl
Dim value As Boolean
 
instance.IsSelected = value
 
value = instance.IsSelected

[CategoryAttribute("Common Properties")]
public bool IsSelected {get; set;}

public read-write property IsSelected: Boolean; 

CategoryAttribute("Common Properties")
public function get,set IsSelected : boolean

[CategoryAttribute("Common Properties")]
public: __property bool get_IsSelected();
public: __property void set_IsSelected( 
   bool value
);

[CategoryAttribute("Common Properties")]
public:
property bool IsSelected {
   bool get();
   void set (    bool value);
}

<Intersoft:DockPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <Intersoft:UXListBox x:Name="ListBox1" HorizontalAlignment="Center" VerticalAlignment="Center">
                <Intersoft:UXListBoxItem Content="Item #1" IsSelected="True"/>
                <Intersoft:UXListBoxItem Content="Item #2"/>
                <Intersoft:UXListBoxItem Content="Item #3"/>
                <Intersoft:UXListBoxItem Content="Item #4"/>
        </Intersoft:UXListBox>
        <Intersoft:FieldLabel Intersoft:DockPanel.Dock="Top" Header="SelectedIndex">
                <TextBlock Text="{Binding SelectedIndex, ElementName=ListBox1}" Margin="4"/>
        </Intersoft:FieldLabel>
        <Intersoft:FieldLabel Intersoft:DockPanel.Dock="Top" Header="SelectedItem">
                <TextBlock Text="{Binding SelectedItem.Content, ElementName=ListBox1}" Margin="4"/>
        </Intersoft:FieldLabel>
        <Button Intersoft:DockPanel.Dock="Top" Content="Set Item #4.IsSelected = True" Margin="4" Click="Button_Click"/>          
</Intersoft:DockPanel>

private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
{
    ((UXListBoxItem)this.ListBox1.Items[3]).IsSelected = true;
}