Android: endless scrolling - ListView and Cursor

问题

I have DB table with ~15,000 rows which I want to display in the listview. I want to display first 100 and when the user scrolls down to the last item the next 100 should be loaded (an so on...). I have implemented on OnScrollListener() which calls AsyncTask responsible for loading more items. The problem I've got is that my SimpleCursorAdapter is not updated after more rows are added to the cursor. I have tried adapter.notifyDataSetChanged(); but that doesn't do anything.

This is the list listener:

    myListView.setOnScrollListener(new OnScrollListener(){
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            int lastInScreen = firstVisibleItem + visibleItemCount;
            if(resultCursor != null){
                if(lastInScreen == totalItemCount && isLoadingMore == false){
                    isLoadingMore = true;
                    loadedPage ++;
                    new LoadBooks().execute();
                }
            }
        }
        public void onScrollStateChanged(AbsListView view, int scrollState) {}
    });

This is my AsyncTask class:

private class LoadBooks extends AsyncTask<String, Void, Void> {
    private final ProgressDialog dialog = new ProgressDialog(FullIndex.this);

    @Override
    protected void onPreExecute() {
       this.dialog.setMessage("Loading books...");
       this.dialog.show();
    }

    @Override
    protected Void doInBackground(String... arg0) {
        try{
            resultCursor = dbHelper.fetchBooks(0, loadedPage * LIMIT_RESULTS);
        }catch(Exception e){
            e.printStackTrace();
        }
        return null;
    }
    @Override
    protected void onPostExecute(final Void unused){
        if(resultCursor != null){
            if(adapter == null){
                startManagingCursor(resultCursor);
                String[] from = new String[]{"name"};
                int[] to = new int[]{R.id.book_item_tbx};
                getListView().setTranscriptMode(ListView.TRANSCRIPT_MODE_NORMAL);
                adapter = new SimpleCursorAdapter(FullIndex.this, R.layout.book_item, resultCursor, from, to);
                setListAdapter(adp);
            }else{
                adapter.notifyDataSetChanged();
            }
        }
        if(dialog != null && dialog.isShowing()){
            dialog.dismiss();
        }
        isLoadingMore = false;
    }
}

New rows are added to resultCursor but the list is not updated, what am I missing?

回答1:

I will post a code which I have used to populated 10 records each on scroll event.

  /**
     * Called when the activity is first created.
     * 
     * @param savedInstanceState
     *            the saved instance state
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
             super.onCreate(savedInstanceState);
             setContentView(R.layout.view_checkin_checkout_history);

             Thread thread = new Thread() {

            public void run() {

                       synchronized (this) {
                    fetchHistory(0);

                    handler.post(new Runnable() {
                        public void run() {
                            pd.dismiss();

                            displayUI();
                        };
                    });
                }
            }
        };

        thread.start();
         }

       /**
     * Display the check in check out history list.
     */
    private void displayUI() {
        if ((checkInCheckOutHistoryList != null)
                && (checkInCheckOutHistoryList.size() > 0)) {
            historyArrayList = new ArrayList<HashMap<String, String>>();

            histroyListAdapter = new SimpleAdapter(
                    ViewCheckInCheckOutHistory.this, historyArrayList,
                    R.layout.multi_colummn_list_text_style_small, new String[] {
                            "assetTag", "gif" , "action", "actionTime"},
                    new int[] { R.id.list_content_column1,
                            R.id.list_content_imagecolumn,
                            R.id.list_content_column3,
                            R.id.list_content_column4});

            // To add more items to list view on scroll event.
            historyListView.setOnScrollListener(new OnScrollListener() {

                @Override
                public void onScrollStateChanged(AbsListView view,
                        int scrollState) {
                }

                @Override
                public void onScroll(AbsListView view, int firstVisibleItem,
                        int visibleItemCount, int totalItemCount) {

                    int lastInScreen = firstVisibleItem + visibleItemCount;

                    if ((lastInScreen == totalItemCount) && !(loadingMore) && (lastInScreen < totalHistoryItemCount)) {

                        if (!firstInstance) {
                            openSlider();                           
                        }                           

                        fetchHistory(lastInScreen);     

                        Thread thread = new Thread(null, loadMoreListItems);
                        thread.start();
                    }
                }
            });
                     }
                  }

// Runnable to load the items

    private Runnable loadMoreListItems = new Runnable() {

        @Override
        synchronized public void run() {
            // Set flag so we cant load new items 2 at the same time
            loadingMore = true;

            HashMap<String, String> historyObjectMap;

            for (CheckInCheckOutHistory checkOutHistoryObj : checkInCheckOutHistoryList) {
                historyObjectMap = new HashMap<String, String>();
                historyObjectMap.put("assetTag",
                        checkOutHistoryObj.getAssetTag());
                historyObjectMap.put("action", checkOutHistoryObj.getAction());
                historyObjectMap.put("actionTime",
                        checkOutHistoryObj.getActionDate());

                if (checkOutHistoryObj.getAction().equals("Checked out")) {
                    historyObjectMap.put("gif", R.drawable.radio_button_yellow
                            + "");
                } else {
                    historyObjectMap.put("gif", R.drawable.radio_button_green
                            + "");
                }

                historyArrayList.add(historyObjectMap);
            }

            runOnUiThread(returnRes);
        }
    };

    // Since we cant update our UI from a thread this Runnable takes care of
    // that!
    private Runnable returnRes = new Runnable() {
        @Override
        public void run() {

            // Add the new items to the adapter
            if (historyArrayList != null && historyArrayList.size() > 0) {
                histroyListAdapter.notifyDataSetChanged();
            }

            if (firstInstance) {
                historyListView.setAdapter(histroyListAdapter);
                firstInstance = false;
            }

            historyListLayout.setVisibility(View.VISIBLE);

            // Done loading more.
            loadingMore = false;

            if ((slidingDrawer.isOpened()) && (!loadingMore)) {

                handler.postDelayed(new Runnable() {

                    @Override
                    public void run() {
                        slidingDrawer.close();
                        slidingDrawer.setVisibility(View.GONE);
                    }
                }, 1000);

            }
        }
    };

fetchHistory(int count) is the method I have used to set the values for totalHistoryItemCount & checkInCheckOutHistoryList.

Hope this would help.

来源：https://stackoverflow.com/questions/6573489/android-endless-scrolling-listview-and-cursor