android - 在方向更改时保存 fragment 状态

我正在为Android创建一个文件管理器应用程序，下面的两个类是执行此操作的大部分逻辑。我正在做的是在ContentList启动时，将ContentListFragment添加到ContestList xml中的容器布局中。通过添加ContentListFragment，我得到了当前路径，然后调用setFileDir(String S)，该方法基本上在传入的路径中获取File，在该位置获取Files列表，初始化数组，然后初始化适配器。然后，我设置适配器，设置操作栏UI和上下文操作栏。现在，每次按下ContentListFragment上的项目时，它将使用所选项目的路径创建另一个ContentListFragment。然后将之前的 fragment 添加到后堆栈中。既然一切都很好，但当定向发生时，问题就来了。

ContentListFragment的onCreate中的setRetainInstance(true)是唯一可以防止整个应用程序在更改方向时强制关闭的东西。但是，以这种方式进行操作会使应用程序稍后在稍后返回时强制关闭(这是我遇到的主要问题，无法理解原因)。

当尝试在方向更改时重新创建“Activity ”时，我试图用一个新的ContentListFragment替换它(此代码不在下面)，但是该应用程序也通过setFileDir()处的NullPointerException关闭，因此其他所有内容都崩溃了。

如何保存 fragment 状态，以便在方向更改时所有内容都保持与方向更改之前相同的状态，并且如果没有它，则在稍后过一会儿返回时会强制关闭吗？

以防万一，我的应用只是一个带有递归ContentListFragments的Activity。

public class ContentList extends DrawerActivity implements ContentListFragment.listFragmentListener{

    // instance variables
    private FragmentManager fm;
    private FragmentTransaction ft;
    private String currentPath;

    // Initializes variables.
    // If Activity is started for the first time, a path to the storage is
    // received.
    // Else, if it's an orientation change, the path is just retained.
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.content_list);

        if (savedInstanceState == null) {
            fm = getSupportFragmentManager();
            ft = fm.beginTransaction();
            File file = Environment.getExternalStorageDirectory();
            currentPath = file.getPath();
            ft.add(R.id.content_container_fragment_listview, new ContentListFragment());
            ft.commit();
        } else {
            fm = getSupportFragmentManager();
            currentPath = savedInstanceState.getString("PATH");
        }
    }

    // Grabs the currentPath in case of orientation changes.
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("PATH", currentPath);
    }

dfsas

public class ContentListFragment extends SherlockListFragment {

    // instance variables
    private ArrayList<Item> items;
    private ArrayList<Item> copy_move_queue_items;
    private ItemAdapter adapter;
    private listFragmentListener lfListener;
    private String currentPath;
    private MenuItem menuItemRename;

    // instantiates variables using setFileDir() and the path from the container Activity.
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
        currentPath = ((ContentList) getActivity()).getCurrentPath();
        setFileDir(currentPath);

    }

    // Gets a reference to Activity interface
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            lfListener = (listFragmentListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + "must implement listFragmentListener");
        }
    }

    // Sets the UI of the listView and the ActionBar
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.content_list_fragment, container, false);

        File file = Environment.getExternalStorageDirectory();
        String rootPath = file.getPath();

        // Sets Action Bar title to current directory, and creates an Up
        // affordance if the root path doesn't equal the current Path
        getSherlockActivity().getSupportActionBar().setTitle(null);
        getSherlockActivity().getSupportActionBar().setLogo(R.drawable.ab_icon);

        if (currentPath.equals(rootPath)) {
            getSherlockActivity().getSupportActionBar()
                    .setDisplayHomeAsUpEnabled(false);
            getSherlockActivity().getSupportActionBar()
                    .setHomeButtonEnabled(false);
        } else {
            getSherlockActivity().getSupportActionBar()
                    .setDisplayHomeAsUpEnabled(true);



            // getSherlockActivity().getSupportActionBar().setTitle("/" +
            // (currentPath.substring(currentPath.lastIndexOf("/") +1)));
        }

        return v;

    }

    // Sets the long click Contextual Action Mode to the ListView
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        setActionMode();
        setListAdapter(adapter);
    }
    // Gets the list of files at the path and adds them to the Item ArrayList,
// initializing the adapter as well
public void setFileDir(String path) {
    File file = new File(path);
    File[] files = file.listFiles();
    Arrays.sort(files, new fileComparator());
    items = new ArrayList<Item>();
    for (File f : files) {
        items.add(new Item(f));
    }
    adapter = new ItemAdapter(getActivity(), R.layout.content_list_item, items);
}

最佳答案

@Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        onCreate(savedInstanceState);
    }

关于android - 在方向更改时保存 fragment 状态，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/13986630/