问getActivity（）在Fragment函数中返回null？

public void asd() {
    if (getActivity() == null) {
        Log.d("yes","it is null");
    }
}

FragmentTransaction transaction1 = getSupportFragmentManager().beginTransaction();
F1 f1 = new F1();
transaction1.replace(R.id.upperPart, f1);
transaction1.commit();
f1.asd();