title: The nav header print @={loginViewModel.userId} instead of the data, why?
body: <p>Hi I have an Activity with a drawer menu like the next:</p>
  
  <p><strong>MapActivity.java</strong></p>
  
  <p>Here setup the data binding like in other activities of the apps</p>
  
  <pre><code>public class MapActivity extends BaseActivity{
      private LoginViewModel loginViewModel;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          ActivityMapBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_map);
          loginViewModel = ViewModelProviders.of(this).get(LoginViewModel.class);
          binding.setLoginViewModel(loginViewModel);
          binding.setLifecycleOwner(this);
  </code></pre>
  
  <p><strong>activity_map.xml</strong></p>
  
  <p>Here ser reference to ViewModel like in other layouts of this app.</p>
  
  <pre><code>?xml version="1.0" encoding="utf-8"?&gt;
  &lt;layout&gt;
      &lt;data&gt;
  
          &lt;variable
              name="loginViewModel"
              type="com.myapp.login.LoginViewModel" /&gt;
      &lt;/data&gt;
      &lt;android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:app="http://schemas.android.com/apk/res-auto"
          xmlns:tools="http://schemas.android.com/tools"
          android:id="@+id/drawer_layout"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:fitsSystemWindows="true"
          tools:openDrawer="start"&gt;
  
          &lt;include
              layout="@layout/app_bar_map"
              android:layout_width="match_parent"
              android:layout_height="match_parent" /&gt;
  
          &lt;android.support.design.widget.NavigationView
              android:id="@+id/nav_view"
              android:layout_width="wrap_content"
              android:layout_height="match_parent"
              android:layout_gravity="start"
              android:fitsSystemWindows="true"
              app:headerLayout="@layout/nav_header_map"
              app:menu="@menu/activity_map_drawer" /&gt;
  
      &lt;/android.support.v4.widget.DrawerLayout&gt;
  &lt;/layout&gt;
  </code></pre>
  
  <p><strong>nav_header_map.xml</strong></p>
  
  <p>And this set the reference to the LoginViewModel.userId</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
      &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:app="http://schemas.android.com/apk/res-auto"
          android:layout_width="match_parent"
          android:layout_height="@dimen/nav_header_height"
          android:background="@drawable/background_gradient"
          android:gravity="bottom"
          android:orientation="vertical"
          android:paddingLeft="@dimen/activity_horizontal_margin"
          android:paddingTop="@dimen/activity_vertical_margin"
          android:paddingRight="@dimen/activity_horizontal_margin"
          android:paddingBottom="@dimen/activity_vertical_margin"
          android:theme="@style/ThemeOverlay.AppCompat.Dark"&gt;
  
  
          &lt;android.support.constraint.ConstraintLayout
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:gravity="bottom"
              android:orientation="horizontal"
              android:paddingLeft="@dimen/activity_horizontal_margin"
              android:paddingTop="@dimen/activity_vertical_margin"
              android:paddingRight="@dimen/activity_horizontal_margin"
              android:paddingBottom="@dimen/activity_vertical_margin"
              android:theme="@style/ThemeOverlay.AppCompat.Dark"&gt;
  
              &lt;TextView
                  android:id="@+id/textView"
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                  android:layout_marginStart="16dp"
                  android:layout_marginTop="16dp"
                  android:layout_marginEnd="16dp"
                  android:layout_marginBottom="19dp"
                  android:paddingTop="@dimen/nav_header_vertical_spacing"
                  android:textColor="@color/red"
                  android:text="@={loginViewModel.userId}"
                  android:textAppearance="@style/TextAppearance.AppCompat.Body1"
                  app:layout_constraintBottom_toBottomOf="parent"
                  app:layout_constraintEnd_toEndOf="parent"
                  app:layout_constraintStart_toStartOf="parent"/&gt;
  
          &lt;/android.support.constraint.ConstraintLayout&gt;
  
      &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>The problem is that when open this activity in the nav_heade_map print "@={loginViewModel.userId}" instead of the userId.</p>
  
  <p>How can resolve this for that appear the userId.</p>
  
  <p>Thanks.</p>