title: Determining the SubMenu of a MenuItem
body: <p>I have a <code>NavigationView</code> in my app. Inside the menu for the <code>NavView</code>, I have two sub menus:</p>
  
  <pre><code>&lt;menu xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;item
          android:id="@+id/nav_group_one"
          android:title="SubMenu A"&gt;
          &lt;menu&gt;
              &lt;item
                  android:checkable="true"
                  android:title="One"/&gt;
              &lt;item
                  android:checkable="true"
                  android:title="Two"/&gt;
          &lt;/menu&gt;
      &lt;/item&gt;
  
      &lt;item
          android:id="@+id/nav_group_two"
          android:title="SubMenu B"&gt;
          &lt;menu&gt;
              &lt;item
                  android:checkable="true"
                  android:title="Three"/&gt;
              &lt;item
                  android:checkable="true"
                  android:title="Four"/&gt;
          &lt;/menu&gt;
      &lt;/item&gt;
  &lt;/menu&gt;
  </code></pre>
  
  <p>In my activity's <code>onNavigationItemSelected()</code> I would like to be able to figure out which sub menu the selected item is in. How would I do this?</p>