Android onScroll从MySQL / PHP / JSON加载更多结果

Question

我正在寻找一种方法来将onScroll侦听器强加到我的listview中。我已经阅读了很多关于使用的内容：

notifyDataSetChanged();

但是，老实说，我无法弄清楚如何将其实现到我的工作代码中。

目前，我使用PHP（JSON Response）从MySQL数据库中将一堆记录放入listview。一切正常，但我想限制首次启动活动时返回的记录数（我知道这是用PHP脚本中的SQL语句完成的），然后当用户滚动加载旧帖子并附加它们时到当前列表视图。我查看过NUMEROUS个例子，但是找不到与我目前的结构有关的任何例子。

这是我目前的代码：（LiveFeed.java）

public class LiveFeed extends SherlockListActivity {
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Used To Put Dark Icons On Light Action Bar
    boolean isLight = ThemeList.THEME == R.style.Theme_Sherlock;

    // Build Action Bar
    menu.add("Refresh")
        .setIcon(isLight ? R.drawable.ic_refresh : R.drawable.ic_refresh_inverse).setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);

    menu.add("+ Add Post")
        .setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM | MenuItem.SHOW_AS_ACTION_WITH_TEXT);
    return true;
}

// Define Menu Item Actions
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    String menuItemTitle = item.getTitle().toString();
    if(menuItemTitle.equals("Refresh")){
        // Clear ArrayList
        posts.clear();
        // Re-Run AsyncTask
        new FeedTask().execute();
    }
    if(menuItemTitle.equals("+ Add Post")){
        Intent intent = new Intent(this, AddPost.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(intent);
    }
    return true;
}

private ArrayList<Feed> posts = new ArrayList<Feed>();

// Define JSON Nodes
private static final String TAG_ID = "id";
private static final String TAG_POST = "post";
private static final String TAG_TIME = "post_time";

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

    // Load All Posts
    new FeedTask().execute();

    // Get ListView
    ListView lv = getListView();

    // Selecting Single List Item Starts EditPost Activity
    lv.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            // getting values from selected ListItem
            String pid = ((TextView) view.findViewById(R.id.postid)).getText().toString();
            // Starting new intent
            Intent in = new Intent(getApplicationContext(), EditPost.class);
            // sending Post Id To EditPost Activity
            in.putExtra(TAG_ID, pid);
            // starting new activity and expecting some response back
            startActivityForResult(in, 100);
        }
    });
}

// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    // If Result Code 100 (edited/deleted post) - Reload Screen
    if (resultCode == 100) {
        Intent intent = getIntent();
        finish();
        startActivity(intent);
    }
}

// AsyncTask To Pull In All Posts And Build ListView
private class FeedTask extends AsyncTask<Void, Void, Void> {
    private ProgressDialog progressDialog;
    protected void onPreExecute() {
        progressDialog = ProgressDialog.show(LiveFeed.this,"", "Loading. Please wait...", true);
    }

    @Override
    protected Void doInBackground(Void... arg0) {
        try {
            HttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost("http://www.mysite.com/android/login/get_posts.php");
            HttpResponse httpResponse = httpClient.execute(httpPost);
            String result = EntityUtils.toString(httpResponse.getEntity());
            JSONArray jArray = new JSONArray(result);
            JSONObject json_data = null;
            for (int i = 0; i < jArray.length(); i++) {
                json_data = jArray.getJSONObject(i);
                Feed feed = new Feed();
                feed.id = json_data.getString(TAG_ID);
                feed.post = json_data.getString(TAG_POST);
                feed.post_time = json_data.getString(TAG_TIME);
                posts.add(feed);
            }
        } 
        catch (Exception e){
            Log.e("ERROR", "Error loading JSON", e);
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        progressDialog.dismiss();
        setListAdapter(new FeedListAdaptor(LiveFeed.this, R.layout.feed, posts));
    }
}

private class FeedListAdaptor extends ArrayAdapter<Feed> {
    private ArrayList<Feed> posts;
    public FeedListAdaptor(Context context, int textViewResourceId, ArrayList<Feed> items) {
        super(context, textViewResourceId, items);
        this.posts = items;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater)
            getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.feed, null);
        }
        Feed o = posts.get(position);
        TextView ht = (TextView) v.findViewById(R.id.postid);
        TextView tt = (TextView) v.findViewById(R.id.toptext);
        TextView bt = (TextView) v.findViewById(R.id.bottomtext);
        ht.setText(o.id);
        tt.setText(o.post);
        bt.setText(o.post_time);
        return v;
    }
}

// Define Variables Used To Build Feed
public class Feed {
    String id;
    String post;
    String post_time;
}

}

提取结果的PHP脚本：（get_posts.php）

include('config.php');
$q=mysql_query("SELECT f.id, f.post, DATE_FORMAT(f.post_time, '%b %D, %Y %r') AS post_time, f.updated, u.firstname, u.lastname FROM feed f
INNER JOIN users u ON u.id=f.user__id WHERE archived='0' ORDER BY f.id DESC");
while($row=mysql_fetch_assoc($q))
$output[]=$row;
print json_encode($output);
mysql_close();

我正在考虑在初始帖子中传递一个起始编号来告诉PHP脚本要撤回多少结果。然后在每次在滚动期间获取结果时，返回下一个数字以用作从onScroll（）调用的下一个SQL查询中的LIMIT。 （现在我的SQL查询没有设置任何LIMIT。）

我希望有人可以帮助我！

Answer 1

我目前正在做类似的事情。您可以将setOnScrollListener用于ListView并按如下方式实现：

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

    boolean isLastItemVisible = firstVisibleItem + visibleItemCount == totalItemCount;

    if (isLastItemVisible) {
        listOverscrolled();
    }

}

比listOverscrolled方法做类似的事情：

    if (!isLoadingData()) {
      setLoadingData(true);
      loadData(); 
}

并在loadData方法中启动加载数据的新AsyncTask。 我所做的是将最后下载的记录的id附加到url查询和SQL查询添加条件WHERE id＆gt; last_id。每次请求更多记录时，以相同的顺序返回它们非常重要。

所以在你的情况下，它会是这样的：

 lastId = feedListAdapter.get(feedListAdapter.count());
    ... and in AsyncTask ...
   HttpPost httpPost = new HttpPost("http://www.mysite.com/android/login/get_posts.php?lastid=" + lastId);

比在OnPostExecute中你可以做类似的事情：

 setLoading(false);
    feedListAdapter.addAll(feeds);
    feedListAdapter.notifyDataSetChanged();

当然必须先创建适配器。