I had the same exception with the following code:

public class SelectWeekDayFragment extends DialogFragment {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        return new AlertDialog.Builder(getActivity())
        .setMessage("Are you sure?").setPositiveButton("Ok", null)
        .setNegativeButton("No way", null).create();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.week_day_dialog, container, false);

        return view;    
    }
}

You must choose to override only one of onCreateView or onCreateDialog in a DialogFragment. Overriding both will result in the exception: “requestFeature() must be called before adding content”.

Important

For complete answer check the @TravisChristian comment. As he said, you can override both indeed, but the problem comes when you try to inflate the view after having already creating the dialog view.