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，在启动 ContentList 时，它将 ContentListFragment 添加到 ContestList xml 中的容器布局。通过添加 ContentListFragment，我获取了当前路径，然后调用 setFileDir(String S)，它基本上获取传入路径中的文件，获取该位置的文件列表，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，它都会使用所选项目的路径创建另一个 ContentListFragment。然后将之前的 fragment 添加到返回堆栈。现在一切都很好，但当方向发生时，问题就来了。

ContentListFragment 的 onCreate 中的 setRetainInstance(true) 是唯一防止整个应用程序在应用程序更改方向时强制关闭的方法。但是，这样做会导致应用程序在我稍后返回时强制关闭(这是我遇到的主要问题，并且不明白为什么)。

当在方向更改时重新创建 Activity 时，我尝试用一​​个新的 ContentListFragment 替换当前的 ContentListFragment(此代码不在下面)，但是应用程序强制关闭时也会在 setFileDir() 处出现 NullPointerException，因此其他所有内容都会下降分开。

如何保存 fragment 状态，以便在方向改变时一切都与方向改变前一样，并且在没有它的情况下在我稍后返回时强制关闭？

以防万一，我的应用程序只是一个具有递归 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);
    }

国家安全局

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

this worked for me

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

and in manifest file inside your Activity tag

android:configChanges="orientation|screenSize"

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