title: Default text for checkable combobox
body: <p>I'm using the <strong><a href="https://wpftoolkit.codeplex.com/wikipage?title=CheckComboBox" rel="nofollow noreferrer">Xceed checkable combobox</a></strong>. Now I want to display a default text depending on the selected checkboxes in the combobox but I don't know how to do that.</p>
  
  <p><strong>For example:</strong></p>
  
  <p><img src="https://i.stack.imgur.com/GSLRV.jpg" alt="enter image description here"></p>
  
  <p><strong>The content (red arrow) of the textbox should be:</strong></p>
  
  <ul>
  <li>If nothing is selected: "Please select"</li>
  <li>If everything is selected: "All People"</li>
  <li>If one or more are selected: "Specific selection"</li>
  </ul>
  
  <p><strong>Like:</strong></p>
  
  <p><img src="https://i.stack.imgur.com/yBQyJ.jpg" alt="enter image description here"></p>
  
  <hr>
  
  <p><strong>Example-Code:</strong></p>
  
  <p><strong>XAML:</strong></p>
  
  <pre><code>&lt;Window x:Class="WpfApplication1.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
          Title="MainWindow" Height="350" Width="525"&gt;
      &lt;Grid&gt;
          &lt;xctk:CheckComboBox x:Name="_checkComboBox"
                            Height="22"
                            VerticalAlignment="Stretch"
                            ItemsSource="{Binding Names}"
                            SelectedItemsOverride="{Binding SelectedNames}"
                            DisplayMemberPath="Title"
                            Delimiter=", "
                            Width="100"/&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p><strong>CS:</strong></p>
  
  <pre><code>using System.Windows;
  
  namespace WpfApplication1
  {
      using System.Collections.ObjectModel;
  
      public partial class MainWindow
      {
          public MainWindow()
          {
              InitializeComponent();
              _checkComboBox.DataContext = this;
  
              Names = new ObservableCollection&lt;People&gt;()
                {
                  new People() { Title = "Mikel" },
                  new People() { Title = "Tom" },
                  new People() { Title = "Jennifer" },
                  new People() { Title = "Megan" },
                };
  
              SelectedNames = new ObservableCollection&lt;People&gt;();
          }
  
          public ObservableCollection&lt;People&gt; Names
          {
              get;
              set;
          }
  
          public ObservableCollection&lt;People&gt; SelectedNames
          {
              get;
              set;
          }
      }
  
      public class People
      {
          public string Title
          {
              get;
              set;
          }
      }
  }
  </code></pre>