Question

我在getListView()的{{1}}中致电OnActivityCreated()。它工作正常，但如果我旋转设备屏幕并再次调用getListView（），它将返回null。

这是ListFragment 代码：

ListFragment

这是布局xml（ my_list_fragment.xml ）：

public class MyListFragment extends ListFragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.my_list_fragment, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        ListView list = getListView();

        if (list != null) {
            //List is not null!
        }
        else {
            //List is null, there is an error.
        }
    }

}

Answer 1

我认为你应该在onViewCreated（）中调用它：

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    ListView list = getListView();

    ...
}

Answer 2

这是我的解决方案：

在我的 ListFragment 中，我像这样覆盖 onCreate 方法......

@Override
public void onCreate(Bundle savedState) {
    super.onCreate(savedState);
    setRetainInstance(true); // handle rotations gracefully

    ...
}

在我的 FragmentActivity 中，我在 onCreate 方法中为 FragmentManager 添加了一个标签，就像这样......

@Override
public void onCreate(Bundle savedState) {
    super.onCreate(savedState);

    ...

    // create or retrieve the venue list fragment
    final String venueListTag = VenueListFragment.class.getName();
    final FragmentManager fragmentManager = getSupportFragmentManager();
    VenueListFragment venueListFragment = (VenueListFragment) fragmentManager.findFragmentByTag(venueListTag);
    if (venueListFragment == null) {
        venueListFragment = new VenueListFragment();
        final FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.main, venueListFragment, venueListTag);
        fragmentTransaction.commit();
    }

    ...
}

如果您有兴趣，

here更多关于 setRetainInstance 。我不确定Android团队是否对使用 setRetainInstance 感到不满，但他们肯定会保守秘密

ListFragment getListView（）在屏幕旋转后返回null

2 个答案: