Get selected item count from ListBox

   
  
<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        x:Class="AboutDialog" ListBox.SelectionChanged="ListBox_SelectionChanged"
        Button.Click="Button_Click"
        Title="About WPF Unleashed" SizeToContent="WidthAndHeight"
        Background="OrangeRed">
  <StackPanel>
    <Label FontWeight="Bold" FontSize="20" Foreground="White">
      WPF
    </Label>
    <Label>License</Label>
    <Label>Installed Dll:</Label>
    <ListBox>
      <ListBoxItem>1</ListBoxItem>
      <ListBoxItem>2</ListBoxItem>
      <ListBoxItem>3</ListBoxItem>
      <ListBoxItem>4</ListBoxItem>
      <ListBoxItem>5</ListBoxItem>
      <ListBoxItem>6</ListBoxItem>
      <ListBoxItem>7</ListBoxItem>
      <ListBoxItem>8</ListBoxItem>
      <ListBoxItem>9</ListBoxItem>
    </ListBox>
    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
      <Button MinWidth="75" Margin="10">Help</Button>
      <Button MinWidth="75" Margin="10">OK</Button>
    </StackPanel>
    <StatusBar>test</StatusBar>
  </StackPanel>
</Window>
//File:Window.xaml.cs
using System.Windows;
using System.Windows.Controls;

public partial class AboutDialog : Window
{
    public AboutDialog()
    {
        InitializeComponent();
    }

    void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (e.AddedItems.Count > 0)
            MessageBox.Show("You just selected " + e.AddedItems[0]);
    }

    void Button_Click(object sender, RoutedEventArgs e)
    {
        MessageBox.Show("You just clicked " + e.Source);
    }
}