小编iva*_*422的帖子

我想在“片段工具栏”中显示“后退箭头”。我试图写这段代码： ((AppCompatActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);

但AS写道：方法调用..可能会产生“ java.lang.NullPointerException”。关于getSupportActionBar（），AS写入无法解析方法。怎么了？这是我的代码：

public class AddFilterFrag extends android.app.Fragment  {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);       
        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.add_filter_layout, container, false);
        ((AppCompatActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        return rootView;
    }
 @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);

       inflater.inflate(R.menu.fragment_menu, menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (item.getItemId() == android.R.id.home) {
            //something to do
            return true;
        }
        return super.onOptionsItemSelected(item);
    }