android - Android: BackStack を使用したフラグメントの NullPointerException

Question

Android でマスターディテールフラグメントを使用します。ItemListFragment のコールバックに応答する ItemListActivity があります。ListFragment 内の項目がクリックされると、アクティビティ内のコールバックが発生します。次に、スマートフォンとタブレットのどちらを使用するかが決定され、それに応じて新しいアクティビティ/フラグメントが作成されます。

この問題は、スマートフォンを使用して発生します。ItemListFragment 内のアイテムをクリックすると、ItemDetailFragment で新しい ItemDetailActivity が開始されます。ActionBar の Up Navigation を使用して ItemListFragment に戻りたいのですが、NullPointerException が発生します。

私のItemListFragment：

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

        Log.d("debug","Hallo in ItemListFragment");

        //show ActionBar
        setHasOptionsMenu(true);

        //get reference to activity
        myApp = getActivity().getApplication();

        feed = (RSSFeed) getActivity().getIntent().getExtras().get("feed");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
            Bundle savedInstanceState) {
        //inflate the fragment with the custom detail fragment
        View view = inflater.inflate(R.layout.feed_list, null);
        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        //get listview from layout
        lv = getListView();
        lv.setVerticalFadingEdgeEnabled(true);

        // Set custom list adapter to the ListView        
        adapter = new CustomListAdapter(getActivity(), feed);
        lv.setAdapter(adapter);

    }

    //Inflate ActionBar
    @Override
    public void onCreateOptionsMenu(Menu optionsMenu, MenuInflater inflater) {
        inflater.inflate(R.menu.main, optionsMenu);
    }

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

        // Restore the previously serialized activated item position.
        if (savedInstanceState != null
                && savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
            setActivatedPosition(savedInstanceState.getInt(STATE_ACTIVATED_POSITION));
        }
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        // Activities containing this fragment must implement its callbacks.
        if (!(activity instanceof Callbacks)) {
            throw new IllegalStateException("Activity must implement fragment's callbacks.");
        }

        mCallbacks = (Callbacks) activity;
    }

    @Override
    public void onDetach() {
        super.onDetach();

        // Reset the active callbacks interface to the dummy implementation.
        mCallbacks = sDummyCallbacks;
    }

    @Override
    public void onListItemClick(ListView listView, View view, int position, long id) {
        super.onListItemClick(listView, view, position, id);

        // Notify the active callbacks interface (the activity, if the
        // fragment is attached to one) that an item has been selected.
        if (mCallbacks != null) {
            Log.d("debug","Callback in ItemListFragment mit Position: "+position+"und Feed: "+feed);
            mCallbacks.onItemSelected(position, feed);
        }
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);

        if (mActivatedPosition != ListView.INVALID_POSITION) {
            // Serialize and persist the activated item position.
            outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
        }
    }

    /**
     * Turns on activate-on-click mode. When this mode is on, list items will be
     * given the 'activated' state when touched.
     */
    public void setActivateOnItemClick(boolean activateOnItemClick) {
        // When setting CHOICE_MODE_SINGLE, ListView will automatically
        // give items the 'activated' state when touched.
        getListView().setChoiceMode(activateOnItemClick
                ? ListView.CHOICE_MODE_SINGLE
                        : ListView.CHOICE_MODE_NONE);
    }

    private void setActivatedPosition(int position) {
        if (position == ListView.INVALID_POSITION) {
            getListView().setItemChecked(mActivatedPosition, false);
        } else {
            getListView().setItemChecked(position, true);
        }

        mActivatedPosition = position;
    }

    //OnClick auf ActionBar
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case android.R.id.home:
            return true;
        case R.id.refresh_option:
            refreshList(item);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    //Click on refresh in ActionBar -> Refresh the List
    public void refreshList(final MenuItem item) {
        /* Attach a rotating ImageView to the refresh item as an ActionView */
        LayoutInflater inflater = (LayoutInflater) getActivity().getApplication()
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        ImageView iv = (ImageView) inflater.inflate(R.layout.action_refresh,
                null);

        Animation rotation = AnimationUtils.loadAnimation(getActivity(),
                R.anim.refresh_rotate);
        rotation.setRepeatCount(Animation.INFINITE);
        iv.startAnimation(rotation);

        item.setActionView(iv);

        // trigger feed refresh:
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                DOMParser tmpDOMParser = new DOMParser();
                feed = tmpDOMParser.parseXml("http://www.androidcentral.com/feed");

                Log.d("debug", "Refresh Liste mit Feed: "+feed);

                ItemListFragment.this.getActivity().runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                        if (feed != null && feed.getItemCount() > 0) {
                            Log.d("debug", "Aktualisiere Liste");
                            adapter.notifyDataSetChanged();
                            lv.setAdapter(adapter);
                            item.getActionView().clearAnimation();
                            item.setActionView(null);
                        }
                    }
                });
            }
        });
        thread.start();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        adapter.imageLoader.clearCache();
        adapter.notifyDataSetChanged();
    }

私のItemListActivity：

public class ItemListActivity extends FragmentActivity
        implements ItemListFragment.Callbacks {

    /**
     * Whether or not the activity is in two-pane mode, i.e. running on a tablet
     * device.
     */
    private boolean mTwoPane;

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

        Log.d("debug","Hallo in der ItemListActivity");

        //load static ItemListFragment in single pane
        //in two pane load also ItemListFragment static and
        //add item_detail_container in activity_item_detail
        setContentView(R.layout.activity_item_list);

        if (findViewById(R.id.item_detail_container) != null) {
            // The detail container view will be present only in the
            // large-screen layouts (res/values-large and
            // res/values-sw600dp). If this view is present, then the
            // activity should be in two-pane mode.
            mTwoPane = true;

            // In two-pane mode, list items should be given the
            // 'activated' state when touched.
            //TODO aktivierte Listelement anzeigen
            ((ItemListFragment) getSupportFragmentManager()
                    .findFragmentById(R.id.item_list))
                    .setActivateOnItemClick(true);
        }
    }

    /**
     * Inflate ActionBar
     */
    public void onCreateOptionsMenu(
          Menu menu, MenuInflater inflater) {
       inflater.inflate(R.menu.main, menu);
    }

    /**
     * Callback method from {@link ItemListFragment.Callbacks}
     * indicating that the item with the given ID was selected.
     */
    @Override
    public void onItemSelected(int id, RSSFeed feed) {
        if (mTwoPane) {
            // In two-pane mode, show the detail view in this activity by
            // adding or replacing the detail fragment using a
            // fragment transaction.

            Log.d("debug","TwoPane Modus: Callback Methode in der ItemListActivity "
                + "mit Position: "+id+"und Feed: "+feed);

            Bundle arguments = new Bundle();

            arguments.putSerializable("feed", feed);
            arguments.putInt("pos", id);    

            //arguments.putLong(ItemDetailFragment.ARG_ITEM_ID, id);
            ItemDetailFragment fragment = new ItemDetailFragment();
            fragment.setArguments(arguments);
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.item_detail_container, fragment)
                    .addToBackStack(null)
                    .commit();

        } else {
            // In single-pane mode, simply start the detail activity for the selected item ID.

            Log.d("debug","SinglePane Modus: Callback Methode in der ItemListActivity");

            Intent detailIntent = new Intent(this, ItemDetailActivity.class);
            detailIntent.putExtra("pos", id);
            detailIntent.putExtra("feed", feed);
            startActivity(detailIntent);
        }
    }

MyItemDetaiFragment:

public class ItemDetailFragment extends Fragment{

    private int fPos;
    RSSFeed fFeed;
    private ShareActionProvider mShareActionProvider;

    /**
     * Mandatory empty constructor for the fragment manager to instantiate the
     * fragment (e.g. upon screen orientation changes).
     */
    public ItemDetailFragment() {
    }

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

        //show ActionBar
        setHasOptionsMenu(true);

        //get data from DetailActivity
        fFeed = (RSSFeed) getArguments().getSerializable("feed");
        fPos = getArguments().getInt("pos");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        //inflate the fragment with the custom detail fragment
        View view = inflater
                .inflate(R.layout.detail_fragment, container, false);

        return view;
    }

    @SuppressLint("SetJavaScriptEnabled")
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        // Initialize views after the activity is created
        TextView title = (TextView) getView().findViewById(R.id.title);
        TextView author = (TextView) getView().findViewById(R.id.author);
        TextView date = (TextView) getView().findViewById(R.id.date);
        WebView wv = (WebView) getView().findViewById(R.id.desc);

        // Enable the vertical fading edge (by default it is disabled)
        ScrollView sv = (ScrollView) getView().findViewById(R.id.sv);
        sv.setVerticalFadingEdgeEnabled(true);

        // Set webview properties
        WebSettings ws = wv.getSettings();
        //to show only one column, so that picture is always scaled correctly
        ws.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
        ws.setJavaScriptEnabled(true);

        Log.d("debug","In ItemDetailFragment mit Position: "+fPos+"und Feed: "+fFeed);

        //put in data
        title.setText(fFeed.getItem(fPos).getTitle());
        author.setText(fFeed.getItem(fPos).getAuthor());
        date.setText(fFeed.getItem(fPos).getDate());
        wv.loadDataWithBaseURL("http://www.androidcentral.com/", fFeed
                .getItem(fPos).getDescription(), "text/html", "UTF-8", null);

    }

    //show share button in actionbar
    @Override
    public void onCreateOptionsMenu(Menu optionsMenu, MenuInflater inflater) {
        inflater.inflate(R.menu.activity_desc, optionsMenu);

        //get data from DetailActivity
        fFeed = (RSSFeed) getArguments().getSerializable("feed");
        fPos = getArguments().getInt("pos");

        // Locate MenuItem with ShareActionProvider
        MenuItem shareItem = optionsMenu.findItem(R.id.share_option);

        // Fetch and store ShareActionProvider
        mShareActionProvider = (ShareActionProvider) shareItem
                .getActionProvider();

        Intent shareIntent = new Intent(Intent.ACTION_SEND);
        shareIntent.setType("text/plain");
        shareIntent.putExtra(Intent.EXTRA_SUBJECT, "RSS");

        String shareBody = fFeed.getItem(fPos).getTitle() + " - "
                + fFeed.getItem(fPos).getLink();

        shareIntent.putExtra(Intent.EXTRA_TEXT, shareBody);

        // Set the share intent
        mShareActionProvider.setShareIntent(shareIntent);
    }

    //OnClick auf ActionBar
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case android.R.id.home: 
            android.app.FragmentManager man = getActivity().getFragmentManager();
            man.popBackStackImmediate();
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

}

LogCat 出力:

11-13 21:33:05.848: E/AndroidRuntime(26792): FATAL EXCEPTION: main
11-13 21:33:05.848: E/AndroidRuntime(26792): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.example.ItemListActivity}: java.lang.NullPointerException
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2115)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2153)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.ActivityThread.access$700(ActivityThread.java:137)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.os.Looper.loop(Looper.java:137)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.ActivityThread.main(ActivityThread.java:5031)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at java.lang.reflect.Method.invokeNative(Native Method)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at java.lang.reflect.Method.invoke(Method.java:511)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:115)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at dalvik.system.NativeStart.main(Native Method)
11-13 21:33:05.848: E/AndroidRuntime(26792): Caused by: java.lang.NullPointerException
11-13 21:33:05.848: E/AndroidRuntime(26792):    at de.example.onActivityCreated(ItemListFragment.java:117)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1508)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1884)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:566)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1163)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.Activity.performStart(Activity.java:5068)
11-13 21:33:05.848: E/AndroidRuntime(26792):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2088)
11-13 21:33:05.848: E/AndroidRuntime(26792):    ... 12 more

エラーは、ItemListFragment の次の行につながります。feed = (RSSFeed) getActivity().getIntent().getExtras().get("feed");

ItemDetailFragment で戻るボタンを押すと、すべて正常に動作しますが、上へのナビゲーションだけでエラーが発生します。私を助けてください;-）

score 0 · Accepted Answer

ItemListFragment の onCreate() を次のように変更しました。

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

    Log.d("debug","Hallo in ItemListFragment");

    //show ActionBar
    setHasOptionsMenu(true);

    //get reference to activity
    myApp = getActivity().getApplication();

    //check if intent from ItemListActivity is null
    Bundle be = getActivity().getIntent().getExtras();
    if (be == null){
        //if null read local feed
        feed = ReadFeed(fileName);
        Log.d("debug", "Lese Feed lokal :"+feed);
    }else{
        //else get extras from the intent
        feed = (RSSFeed) getActivity().getIntent().getExtras().get("feed");
        Log.d("debug", "Intent von ItemListActivity an ItemListFragment vorhanden");
    }

}

そしてこの機能を追加しました：

/**
 *  Method to read the feed from the file
 **/
private RSSFeed ReadFeed(String fName) {

    FileInputStream fIn = null;
    ObjectInputStream isr = null;

    RSSFeed _feed = null;
    File feedFile = getActivity().getBaseContext().getFileStreamPath(fileName);
    if (!feedFile.exists())
        return null;

    try {
        fIn = getActivity().openFileInput(fName);
        isr = new ObjectInputStream(fIn);

        _feed = (RSSFeed) isr.readObject();
    }
    catch (Exception e) {
        e.printStackTrace();
    }
    finally {
        try {
            fIn.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return _feed;
}

もちろん、XML フィードを初めて解析するメインアクティビティでも同様の書き込みメソッドを使用します。

ItemDetailFragment で、ActionBar ナビゲーションのすべてのコードを削除し、正常に動作するようになりました!

android - Android: BackStack を使用したフラグメントの NullPointerException

1 に答える 1

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