title: app:visibleGone cannot resolve on android Databinding
body: <p>When I build the project. I'm getting error on app:visibleGone </p>
  
  <p>I'm also enable true to dataBinding in build.gradle and using android architecture components and mvvm.
  project <code>targetSdkVersion</code> is  <code>26</code> and <code>support lib version is 26.0.1</code>.</p>
  
  <p>Below is the error message</p>
  
  <p><a href="https://i.stack.imgur.com/FOblZ.png" rel="noreferrer"><img src="https://i.stack.imgur.com/FOblZ.png" alt="enter image description here"></a></p>
  
  <pre><code>error: package com.****.****.databinding does not exist
  error: cannot find symbol class ActivityMainBinding
  Cannot find the setter for attribute 'app:visibleGone' with parameter type boolean on android.widget.Button.
  </code></pre>
  
  <p>here is my <strong><em>activity_main.xml</em></strong></p>
  
  <pre><code>&lt;layout xmlns:app="http://schemas.android.com/apk/res-auto"&gt;
  
      &lt;data&gt;
  
          &lt;variable
              name="loading"
              type="boolean" /&gt;
  
      &lt;/data&gt;
  
      &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  
          xmlns:tools="http://schemas.android.com/tools"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical"
          tools:context="com.example.aungmyolwin.importdb.MainActivity"&gt;
  
          &lt;Button
              android:id="@+id/btn_load_sql"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Load from SQL"
              app:visibleGone="@{!loading}"/&gt;
  
          &lt;Button
              android:id="@+id/btn_load_room"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Load from Room mapper"
              app:visibleGone="@{!loading}"/&gt;
  
          &lt;TextView
              android:id="@+id/tv_import_loading"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:gravity="center"
              android:text="Importing database...."
              app:visibleGone="@{loading}"/&gt;
  
  
      &lt;/LinearLayout&gt;
  &lt;/layout&gt;
  </code></pre>
  
  <p><strong><em>ActivityMain.java</em></strong> </p>
  
  <pre><code>    @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
  
          binding.btnLoadRoom.setOnClickListener(this);
          binding.btnLoadSql.setOnClickListener(this);
  
          viewModels= ViewModelProviders.of(this).get(MainActivityViewModels.class);
  
      }
  }
  </code></pre>