title: I get a warning saying: is not an activity subclass or alias
body: <p><a href="https://i.stack.imgur.com/818JA.png" rel="nofollow noreferrer">What does the icon next to MapsActivity mean?</a>
  <br>
  When I run the app, it says MapsActivity is not an Activity subclass or alias. 
  That is my mainfest?</p>
  
  <pre><code>    &lt;application
  
          &lt;activity android:name=".MapsActivity"&gt;
              &lt;intent-filter&gt;
                  &lt;action android:name="android.intent.action.MAIN" /&gt;
                  &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
              &lt;/intent-filter&gt;
          &lt;/activity&gt;
  
      &lt;/application&gt;
  
  &lt;/manifest&gt;
  </code></pre>