title: Change a textbox's text value on a UserControl from a Window in WPF
body: <p>I have a UserControl (called <strong>Invoice</strong>) with a textbox (<strong>txtReferenceCode</strong>) hosted in a TabControl (<strong>myTabControl</strong>) on MainWindow.  From the UserControl I call a window (<strong>SearchWindow</strong>) which contains a list of stock items.  The window needs to return a string value to the textbox contained by the UserControl.  I cannot access the textbox on the UserControl from the window and thus cannot pass the string value from the window to the text property. </p>
  
  <p>The UserControl is an instance loaded as a new tabItem (there may be many open as content of tabitems.)  I need to only affect the current tabitem instance of the UserControl.</p>
  
  <p>Eg: (Button Click Event in SearchWindow)</p>
  
  <pre><code>Invoice.txtReferenceCode.Text = SearchWindow.txtReferenceCode.Text
  </code></pre>
  
  <p>I need a simple uncomplicated, solution preferably in VB (but I'll take C# gladly).</p>