title: error: No resource identifier found for attribute 'adSize' in package 'com.google.example' main.xml
body: <p>When I followed the instructions to add an ad into my app by xml, I got the following errors:</p>
  
  <pre><code>Description Resource Path Location Type
  error: No resource identifier found for attribute 'adSize' in package 'com.google.example'  main.xml    /HelloWorld/res/layout  line 12 Android AAPT Problem
  Description Resource Path Location Type
  error: No resource identifier found for attribute 'adUnitId' in package 'com.google.example'    main.xml    /HelloWorld/res/layout  line 12 Android AAPT Problem
  </code></pre>
  
  <p>I did edit the <code>main.xml</code>, add <code>attrs.xml</code> file but the compiler didn't like it.</p>