title: Fragment activity crashes on screen rotate
body: <p>I have a simple fragment activity. In the onCreate() method, I simply add a fragment. The code is posted below. However, each time I rotate the screen, system will call onCreate() again, then it crashes at the super.onCreate() statement; I suppose it is a general Android fragment issue. Can someone help me out? </p>
  
  <pre><code>public class FragActivity extends FragmentActivity {
      @Override
      public void onCreate(Bundle savedState){
          super.onCreate(savedState);
  
          MyFragment frag = new MyFragment();
          getSupportFragmentManager().beginTransaction().replace(android.R.id.content, frag)
          .commit();        
      }
  }
  </code></pre>
  
  <p>The stack trace is attached:</p>
  
  <blockquote>
    <p>java.lang.RuntimeException: Unable to start activity ComponentInfo{}: 
    android.support.v4.app.Fragment$InstantiationException: Unable to
    instantiate fragment:  make sure class name exists, is public, and has
    an empty constructor that is public</p>
  </blockquote>