title: Binding Dictionary<string,string> to Combobox in SL3
body: <p>I'm trying to do the following. 
  I have a class:</p>
  
  <pre><code>public class TextField {
      public string TextType { get; set; }
  }
  </code></pre>
  
  <p>in my View I created a list:</p>
  
  <pre><code>public TextFieldEditControl()
      {
          InitializeComponent();
  
          Dictionary&lt;string, string&gt; lst = new Dictionary&lt;string, string&gt;();
          lst.Add("SingleLine", "Single line");
          lst.Add("MultiLine", "Multi-line");
          lst.Add("RichText", "Rich text");
          cmbTextType.ItemsSource = lst;
      }
  </code></pre>
  
  <p>in my XAML i have: </p>
  
  <pre><code>&lt;ComboBox x:Name="cmbTextType" DisplayMemberPath="Value" SelectionChanged="cmbTextType_SelectionChanged" 
              SelectedItem="{Binding Path=TextType, Mode=TwoWay}" /&gt;
  </code></pre>
  
  <p>The problem is that when I check the value of the TextType property, it returns a string like that: "[SingleLine, Single line]" instead of just the Key. Where can I set it to return only the key for a Key/Value Pair?</p>