title: DataBinding: cannot find symbol class
body: <p>I've got a problem with databinding in android. 
  Above are xml file and activity class:</p>
  
  <p>activity_main.xml ( the binding is in android:enabled="@{loginInfo.existingUser}")</p>
  
  <pre><code> &lt;layout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      xmlns:app="http://schemas.android.com/apk/res-auto"&gt;
  
    &lt;data&gt;
    &lt;variable
     name="loginInfo"
      type="com.example.android.loginapplication.LoginInfo"/&gt;
    &lt;/data&gt;
  
  &lt;LinearLayout
  android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:orientation="vertical"
      android:padding="16dp"&gt;
  
      &lt;RadioGroup
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:orientation="vertical"&gt;
  
          &lt;RadioButton
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="@string/new_customer"
              android:enabled="@{loginInfo.existingUser}"/&gt;
  
          &lt;RadioButton
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="@string/i_have_a_password"/&gt;
      &lt;/RadioGroup&gt;
  
      &lt;EditText
      android:id="@+id/password"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:inputType="textPassword"/&gt;
    &lt;/LinearLayout&gt;
  
    &lt;/layout&gt;
  </code></pre>
  
  <p>LoginInfoActivity.java</p>
  
  <pre><code>public class LoginInfoActivity extends AppCompatActivity {
  
  private LoginInfo loginInfo;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      LoginInfoBinding binding = DataBindingUtil.setContentView(
              this, R.layout.activity_main);
  
  
      binding.setLoginInfo(loginInfo);
  }
  }
  </code></pre>
  
  <p>it can't find generated class LoginInfoBinding in LoginInfoActivity...</p>
  
  <p>is the xml correct? Or it depends by other things?</p>