title: Android, Facebook Login Button Causes Crash (SDK 4.0.0)
body: <p>In my activity <code>.xml</code> file, I include the Facebook Login Button (from <a href="https://developers.facebook.com/docs/facebook-login/android/v2.3" rel="nofollow">this</a> documentation)</p>
  
  <pre><code>    &lt;com.facebook.login.widget.LoginButton
      android:id="@+id/login_button"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center_horizontal"
      android:layout_marginTop="30dp"
      android:layout_marginBottom="30dp" /&gt;
  </code></pre>
  
  <p>Immediately I get a warning saying that</p>
  
  <pre><code>The following classes could not be found:
      - com.facebook.login.widget.LoginButton
  </code></pre>
  
  <p>The documentation says to</p>
  
  <blockquote>
    <p>Add the button to your layout XML file with the full class name,
    com.facebook.widget.LoginButton</p>
  </blockquote>
  
  <p>But changing that top line does nothing. The app crashes immediately, without opening, and nothing is recorded in the log cat (testing on external device).</p>
  
  <p>Removing the button, or changing it to</p>
  
  <pre><code>    &lt;Button
      android:id="@+id/login_button"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center_horizontal"
      android:layout_marginTop="30dp"
      android:layout_marginBottom="30dp" /&gt;
  </code></pre>
  
  <p>stops the crash, but this is my first time working with the Facebook SDK and don't know if the regular button will work.</p>
  
  <p>Thank you in advance.</p>