title: Change Background Color for WPF textbox in changed-state
body: <p>I have a class EmployeeViewModel with 2 properties "FirstName" and "LastName". The class also has a dictionary with the changes of the properties. (The class implements INotifyPropertyChanged and IDataErrorInfo, everything is fine.</p>
  
  <p>In my view there is a textbox:</p>
  
  <pre><code>&lt;TextBox x:Name="firstNameTextBox" Text="{Binding Path=FirstName}" /&gt;
  </code></pre>
  
  <p>How can I change the background color of the textbox, if the original value changed? I thought about creating a trigger which sets the background color but to what should I bind?
  I don't want to created an additional property for every control which holds the state wheter the one was changed or not.</p>
  
  <p>Thx</p>