overide FragmentActivity onSaveInstanceState method like this.
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if(outState != null) {
String FRAGMENTS_TAG = "android:support:fragments";
// remove掉保存的Fragment
outState.remove(FRAGMENTS_TAG);
}
}
[Android Pro] Android Fragment getActivity返回null解决
原文：http://www.cnblogs.com/0616--ataozhijia/p/4863477.html