title: Textbox - bound property value does not update immediately
body: <p>I have a textbox which is bound to a property <code>ItemID</code> like so.</p>
  
  <pre><code>private string _itemID;
  public string ItemID {
      get { return _itemID; }
      set { 
          _itemID = value;
      }
  }
  </code></pre>
  
  <p>The XAML of the text box is as follows:</p>
  
  <pre><code>&lt;TextBox Text="{Binding Path=ItemID, Mode=TwoWay}" Name="txtItemID" /&gt;
  </code></pre>
  
  <p>The problem is, the value of <code>ItemID</code> does not update immediately as I type,<br>
  causing the <code>Add</code> button to be disabled (command), until I lose focus of the text box by pressing the tab key.</p>