title: Error in xml layout, Can't convert to dimension: 15
body: <p>Within my application I have an error in the graphical layout which shows up as:</p>
  
  <pre><code>error!
  UnsupportedOperationException: Can't convert to dimension: 15
  Exception details are logged in Window &gt; Show View &gt; Error LogThe following classes could not be found:
  - TextView
  </code></pre>
  
  <p>When I run the application this works, but it shows the error in the graphical layout, does anyone know the cause of this. </p>
  
  <p>It occurs when I put <code>android:layout_marginTop="-3dip"</code> , if I dont use <code>-</code> then this doesn't show. </p>
  
  <p>Thanks</p>