title: Visibility not working in data binding android
body: <p>I am using the latest data binding in android using android studio 2.1.
  using the visibility tag as describe in the below code getting an error as </p>
  
  <blockquote>
    <p>java.lang.RuntimeException: Found data binding errors.
    / data binding error ****msg:Identifiers must have user defined types from the XML file. View is missing it
    file:D:\HP\HealthPortal_Android\Code\app\src\main\res\layout\cardview_image_twotextview.xml
    loc:68:90 - 68:93
    \ data binding error</p>
  </blockquote>
  
  <pre><code>   &lt;TextView
                          android:id="@+id/card_sub_title"
                          android:layout_width="wrap_content"
                          android:layout_height="wrap_content"
                          android:layout_below="@+id/card_title"
                          android:layout_marginLeft="@dimen/carview_margin"
                          android:layout_toRightOf="@+id/card_image"
                          android:text="@{toolsAndTrackersCards.subtitle}"
                          android:textColor="@color/black"
                          android:textSize="20sp"
                          android:visibility="@{toolsAndTrackersCards.subtitle.equals(@string/Empty_String) ?  View.VISIBLE : View.GONE}"
                          /&gt;
  </code></pre>
  
  <p>Done some google not abel to find the solution. The <strong>@string/Empty_String</strong> is define as empty string "" in string.xml file. where I am doing wrong.</p>
  
  <p><a href="https://stackoverflow.com/questions/35416870/android-data-binding-radio-button-not-updating">Android data binding, Radio Button not updating</a></p>