title: How to use d:DesignInstance with types that don't have default constructor?
body: <p>I am binding a textbox to an object, like so:</p>
  
  <pre><code>  &lt;TextBlock d:DataContext="{d:DesignInstance ViewModel:TaskVM }" 
               Text="{Binding Title}" MouseLeftButtonDown="TextBlock_MouseLeftButtonDown"&gt;
    &lt;/TextBlock&gt;
  </code></pre>
  
  <p>Now I am wondering how to make it display mock data during design. I've tried doing something like that:</p>
  
  <pre><code>  &lt;TextBlock Text="{Binding Path=Title}" MouseLeftButtonDown="TextBlock_MouseLeftButtonDown"&gt;
      &lt;d:DesignProperties.DataContext&gt;
         &lt;ViewModel:TaskVM Title="Mock"/&gt;
      &lt;/d:DesignProperties.DataContext&gt;
    &lt;/TextBlock&gt;
  </code></pre>
  
  <p>However, since TaskVM has no default ctor, I am getting a "No default constructor" found.</p>
  
  <p>I know that when I use <code>d:DataContext="{d:DesignInstance ViewModel:TaskVM }"</code> it creates a mock data type. Is there a way for me to set the properties of this mock type?</p>
  
  <p>Thanks!</p>