title: WPF - ComboBox SelectionChanged => Change TextBox Binding
body: <p>I have a ComboBox and a TextBox. The TextBox is binding to a "default"-property in my ViewModel.</p>
  
  <p>What I'm trying to accomplish is that when I change the Value in the ComboBox , that the property of the TextBox is changed to another property.</p>
  
  <pre><code>&lt;ComboBox SelectedIndex="0" Name="ComboBox1"&gt;
      &lt;ComboBoxItem&gt;
          Messages1
      &lt;/ComboBoxItem&gt;
      &lt;ComboBoxItem&gt;
          Messages2
      &lt;/ComboBoxItem&gt;
  &lt;/ComboBox&gt;
  
   &lt;TextBox Text="{Binding Messages1}" IsReadOnly="True" VerticalScrollBarVisibility="Visible" AcceptsReturn="True" Name="LogTextBox" /&gt;
  </code></pre>
  
  <p>I want to change the binding of the TextBox to Messages2. I tried many things but nothing seems to work.</p>
  
  <p>Is there an easy solution?</p>