android - 重新启动加载程序调用时出错

Question

我有一个将数据加载到列表适配器以显示在屏幕上的 fragment 。当我的应用程序启动时，它会启动一项服务来查找新数据，如果找到， fragment 将需要显示这些数据。目前，我的私有(private)广播接收器实际上是在主要 Activity 上——而不是 fragment 。这对我来说似乎不对，但我看不出如何将通知从广播接收器传递回 fragment ，当它在 fragment 本身上时，我读到的另一个问题是建议这种方法。

使用我在下面发布的代码，当我的广播接收器收到通知并在 fragment 上调用 ​​updateConent 时，我得到了 - 我记录了以下错误:

10-26 20:31:21.328: E/AndroidRuntime(711): FATAL EXCEPTION: main
10-26 20:31:21.328: E/AndroidRuntime(711): java.lang.RuntimeException: Error receiving broadcast Intent { act=updatedata flg=0x10 (has extras) } in com.thedailydigi.dailydigi.Main$1@41458418
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:765)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.os.Handler.handleCallback(Handler.java:615)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.os.Handler.dispatchMessage(Handler.java:92)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.os.Looper.loop(Looper.java:137)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.app.ActivityThread.main(ActivityThread.java:4745)
10-26 20:31:21.328: E/AndroidRuntime(711):  at java.lang.reflect.Method.invokeNative(Native Method)
10-26 20:31:21.328: E/AndroidRuntime(711):  at java.lang.reflect.Method.invoke(Method.java:511)
10-26 20:31:21.328: E/AndroidRuntime(711):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-26 20:31:21.328: E/AndroidRuntime(711):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-26 20:31:21.328: E/AndroidRuntime(711):  at dalvik.system.NativeStart.main(Native Method)
10-26 20:31:21.328: E/AndroidRuntime(711): Caused by: java.lang.IllegalStateException: There is already a listener registered
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.support.v4.content.Loader.registerListener(Loader.java:130)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.support.v4.app.LoaderManagerImpl$LoaderInfo.start(LoaderManager.java:260)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.support.v4.app.LoaderManagerImpl.installLoader(LoaderManager.java:510)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.support.v4.app.LoaderManagerImpl.createAndInstallLoader(LoaderManager.java:497)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.support.v4.app.LoaderManagerImpl.restartLoader(LoaderManager.java:643)
10-26 20:31:21.328: E/AndroidRuntime(711):  at com.thedailydigi.dailydigi.activity.HorizontalListFragment.updateContent(HorizontalListFragment.java:130)
10-26 20:31:21.328: E/AndroidRuntime(711):  at com.thedailydigi.dailydigi.Main$1.onReceive(Main.java:36)
10-26 20:31:21.328: E/AndroidRuntime(711):  at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:755)

我发现“Caused by: java.lang.IllegalStateException: There is already a listener registered”是问题的症结所在，但我没有已注册的监听器？

谁能解释一下a)为什么我目前收到上述错误以及b) 这是否是将附加数据加载到 fragment 中的正确方法？

我的相关类的完整代码如下。感谢您的帮助。

主.java

public class Main extends FragmentActivity   { 

    private static final String LOG_TAG = "dd-Main";

    private HorizontalListFragment mDailyDigiFragment;

      private BroadcastReceiver myReceiver = new BroadcastReceiver() {         
            @Override
            public void onReceive(Context context, Intent intent) {
                //TODO go update the UI from the database

                int newRecords = intent.getIntExtra(DownloadFeedService.DOWNLOADED,0);
                long date = intent.getLongExtra(DownloadFeedService.BEGIN_DATE, DownloadFeedService.NULL_DATE);

                Log.d(LOG_TAG, newRecords + " new records downloaded!");

                if (intent.getStringExtra(DownloadFeedService.KEY).equals(getString(R.string.daily_digi_short))) { 
                        mDailyDigiFragment.updateContent(newRecords, date);
                } else {        
                    //TODO add our other fragments here

                }
            }
        };

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

        Log.v(LOG_TAG, "Main Activity started");

        registerReceiver(myReceiver, new IntentFilter(DownloadFeedService.UPDATEDATA));

        setContentView(R.layout.activity_main);

        if (savedInstanceState == null) {           
            //mDailyDigiFragment = HorizontalListFragment.newInstance(getString(R.string.daily_digi_short), 10, R.drawable.banner_dailydigi, true);
            mDailyDigiFragment = HorizontalListFragment.newInstance(getString(R.string.daily_digi_short), 10, R.drawable.banner_dailydigi, true);
            FragmentTransaction dailyDigiTransaction = getSupportFragmentManager().beginTransaction();
            dailyDigiTransaction.add(R.id.dailydigi, mDailyDigiFragment).commit();

            //TODO instantiate our other fragments here
            /*
            Fragment digiShowFragment = HorizontalListFragment.newInstance(getString(R.string.digi_show_short), 10, R.drawable.banner_digishow, true);
            FragmentTransaction digiShowTransaction = getSupportFragmentManager().beginTransaction();
            digiShowTransaction.add(R.id.digishow, digiShowFragment).commit();*/
        }


    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

Horizo​​ntalListFragment.java

public class HorizontalListFragment extends Fragment
    implements LoaderManager.LoaderCallbacks<ArrayList<RssFeed.Article>> {  

    private ArticleAdapter adapter ;  
    private static final String LOG_TAG = "dd-HorizontalListFragment";

    private static String MAX_LOAD_KEY = "max";
    private static String DATASOURCE_KEY = "key";
    private static String IMAGE_SRC_KEY = "image";
    private static String SHOW_TEXT_OVERLAY = "showOverlay";

    private String mRssFeedKey = "";
    private int mDefaultLoad;
    private int mImageResource = 0;

    //TODO do we want to toggle the overlay on the digishow feed?
    private boolean mShowTextOverlay = true;    
    private HorizontalListView mListView;

    ArticleLoader mLoader; 

    public static HorizontalListFragment newInstance(String key, int max,  int img, boolean showOverlay) {
        HorizontalListFragment myFragment = new HorizontalListFragment();

        Bundle args = new Bundle();
        args.putString(DATASOURCE_KEY, key);
        args.putInt(MAX_LOAD_KEY, max);
        args.putInt(IMAGE_SRC_KEY, img);
        args.putBoolean(SHOW_TEXT_OVERLAY, showOverlay);
        myFragment.setArguments(args);

        return myFragment;

    }

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

        Bundle bundle = this.getArguments();
        mRssFeedKey = bundle.getString(DATASOURCE_KEY);
        mDefaultLoad = bundle.getInt(MAX_LOAD_KEY, getResources().getInteger(R.integer.default_display_max));
        mImageResource = bundle.getInt(IMAGE_SRC_KEY, 0);
        mShowTextOverlay = bundle.getBoolean(SHOW_TEXT_OVERLAY, true);
        mLoader = new ArticleLoader(getActivity(), mRssFeedKey,mDefaultLoad);   

        getActivity().getSupportLoaderManager().initLoader(0, null, this);          

    }
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.horizontal_list_section, container, false);

        ImageView img = (ImageView) view.findViewById(R.id.Header_Image);
        img.setImageResource(mImageResource);       

        mListView = (HorizontalListView) view.findViewById(R.id.hr_listview);

        return view;
    }

    @Override
    public Loader<ArrayList<RssFeed.Article>> onCreateLoader(int arg0, Bundle bundle) { 
        Log.d(LOG_TAG, "onCreateLoader: find " + mDefaultLoad + " articles from " + mRssFeedKey);   
        return mLoader;
    }

    @Override
    public void onLoadFinished(Loader<ArrayList<RssFeed.Article>> arg0, ArrayList<RssFeed.Article> result) {
        Log.d(LOG_TAG, "onLoadFinished with " + result.size() + " records from " + mRssFeedKey);                

        //update the listview with the combined results list
        if (adapter == null) {
             adapter = new ArticleAdapter(this.getActivity(), result,true);
             mListView.setAdapter(adapter);             
        } else {
            insertNewArticles(result);  
            adapter.notifyDataSetChanged();
        }


        //TODO use these methods to reset the list position ?
        //mListView.setSelectionFromTop(currentFirstVisibleItem, 0);
        //mListView.getFirstVisiblePosition();

    }


    @Override
    public void onLoaderReset(Loader<ArrayList<RssFeed.Article>> arg0) {
        Log.v(LOG_TAG, "onLoaderReset");

        // TODO what do we need to do here?


    }

    public void updateContent(int newRecords , long date) {

        if (date == DownloadFeedService.NULL_DATE) {
            Log.d(LOG_TAG, "updateContent requesting " + newRecords + " new records.");

            //this is when some new recent content has been downloaded
            mLoader.setDownloadParameters(newRecords, 0);
            getActivity().getSupportLoaderManager().restartLoader(0, null, this);

        } else {
            //this was probably downloaded cuz we're scrolling near the end
        }

    }

    //both lists should already be sorted in date desc order
    private void insertNewArticles(ArrayList<RssFeed.Article> listB) {
        //TODO - we need to make sure we only add new entries
        int listPosition = 0;
        for (Article a : listB ) {
            for (int i = listPosition; i < adapter.getCount(); i++) {
                Article b = adapter.getItem(i);

                //already in the list - skip over it
                if (a.getInternalId() == b.getInternalId()) {               
                    listPosition = i+1;
                    break;
                }

                //our new item is published after - it shows at the front of the list
                if (a.getPublicationDate().before(b.getPublicationDate())) {
                    adapter.insert(a, i-1);
                    listPosition = i;
                    break;
                }
            }

            //when we get to new items that pre-date our current list items, add them at the end
            if (listPosition == adapter.getCount()) {
                adapter.insert(a, listPosition);
                listPosition++;
            }           
        }

    }

}

文章加载器.java

public class ArticleLoader extends AsyncTaskLoader<ArrayList<RssFeed.Article>> {

    private static final String LOG_TAG = "dd-ArticleLoader";

    ArrayList<RssFeed.Article> mArticles;
    final String mSource;

    int mOffset = 0; 
    int mDownloadCount;

    public ArticleLoader(Context context, String source, int max) {
        super(context);
        mSource = source;
        mDownloadCount = max;
    }

    public void setDownloadParameters(int count, int offset) {
        mOffset = offset;
        mDownloadCount = count;
    }


    /**
     * This is where the bulk of our work is done.  This function is
     * called in a background thread and should generate a new set of
     * data to be published by the loader.
     */
    @Override public ArrayList<RssFeed.Article> loadInBackground() {
       Log.d(LOG_TAG, "loadInBackground: find " + mDownloadCount + " articles from " + mSource);


       mArticles = ArticleManager.findArticles(getContext().getContentResolver(), mSource, mDownloadCount, mOffset);
       return mArticles;
    }

    @Override
    protected void onStartLoading() {
      if(mArticles != null) {
        deliverResult(mArticles);
      } else {
        forceLoad();
      }
    }
}

Answer 1

这里的问题是，当您在 updateContent() 方法中调用 getActivity().getSupportLoaderManager().restartLoader(0, null, this); 时，它再次调用 onCreateLoader(...)。您的 onCreateLoader(..) 方法然后返回与第一次相同的加载程序。这个加载器已经有一个注册的监听器。

要解决这个问题，你只需要onCreateLoader(..)每次返回一个新的加载器。

更改自:

@Override
public Loader<ArrayList<RssFeed.Article>> onCreateLoader(int arg0, Bundle bundle) { 
    Log.d(LOG_TAG, "onCreateLoader: find " + mDefaultLoad + " articles from " + mRssFeedKey);   
    return mLoader;
}

到:

@Override
public Loader<ArrayList<RssFeed.Article>> onCreateLoader(int arg0, Bundle bundle) { 
    Log.d(LOG_TAG, "onCreateLoader: find " + mDefaultLoad + " articles from " + mRssFeedKey);   
    return new ArticleLoader(getActivity(), mRssFeedKey,mDefaultLoad);
}