title: Property Change not showing in Visual Studio designer
body: <p>Using VS2015 I'm adding some custom functionality to a TextBlock for a small app and, since I can't derive from TextBlock itself (it's sealed), I'm deriving from UserControl.</p>
  
  <p>In my xaml file, I have</p>
  
  <pre><code>&lt;TextBlock x:Name="innerText"/&gt;
  </code></pre>
  
  <p>As the only element within the usercontrol.</p>
  
  <p>In my code-behind, I have the following used for accessing the text:</p>
  
  <pre><code>public string Label
  {
      get { return innerText.Text; }
      set {
          if (value != innerText.Text)
          {
              innerText.Text = value;
              var handler = PropertyChanged;
              if (handler != null)
                  handler(this, new PropertyChangedEventArgs("Label"));
          }
      }
  }
  </code></pre>
  
  <p>This works great when I'm running my app. On other pages, I am able to add instances of the control and set the "Label" property correctly. Unfortunately, the value of the "Label" property doesn't carry through to the inner textbox within the designer itself.</p>
  
  <p>How can I get the value to update in the designer? While not strictly necessary (as I said, at run-time it works fine), it would make layout in the designer much easier for me.</p>
  
  <p>Update:
  I also tried using a DependencyProperty, with the same issue. Run-time works great, design-time shows nothing.</p>
  
  <pre><code>public string Label
  {
      get { return GetValue(LabelProperty).ToString(); ; }
      set { SetValue(LabelProperty, value); }
  }
  public static readonly DependencyProperty LabelProperty = DependencyProperty.Register("Label", typeof(string), typeof(AutoSizingText), new PropertyMetadata(string.Empty));
  </code></pre>
  
  <p>And then, in the xaml, I set the DataContext for the entire control:</p>
  
  <pre><code>DataContext="{Binding RelativeSource={RelativeSource Self}}"
  </code></pre>
  
  <p>And tried to bind the Text value:</p>
  
  <pre><code>    &lt;TextBlock Text="{Binding Label}" /&gt;
  </code></pre>