無盡的滾動ListView

Question

我正在填充一個ListView與從在線服務提取的數據，它提供頁面中的數據。當用戶在頁面底部附近滾動時，我試圖自動加載下一頁數據，而不是提供「下一頁」按鈕。

取數據時使用的AsyncTask：

class RecentTracksTask extends AsyncTask<Integer, Void, Void> { 

    ArrayList<Track> recentTracks; 

    @Override 
    protected Void doInBackground(Integer... page) { 
     try { 
      // Get a page of 15 tracks 
      // Simplified - getPage accepts 'page' and 'limit' parameters and returns a Collection<Track> 
      recentTracks = new ArrayList<Track>(getPage(page[0], 15)); 

     } catch() {} 

     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 
      TracksAdapter mTracksAdapter = new TracksAdapter(getActivity(), 
        recentTracks); 

      ListView listView = (ListView) getActivity().findViewById(R.id.listview); 
      listView.setAdapter(mTracksAdapter); 
      listView.setOnScrollListener(new EndlessScrollListener()); 

    } 
} 

和適配器：

class TracksAdapter extends ArrayAdapter<Track> { 
    private final Context context; 
    private final ArrayList<Track> tracks; 

    public TracksAdapter(Context context, 
         ArrayList<Track> recentTrackArrayList) { 
     super(context, 0, recentTrackArrayList); 
     this.context = context; 
     this.tracks = recentTrackArrayList; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     if (convertView == null) { 
      LayoutInflater inflater = (LayoutInflater) context 
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      convertView = inflater.inflate(R.layout.list_item, 
        parent, false); 
     } 

     final Track track = tracks.get(position); 

     final TextView tv = (TextView) convertView 
       .findViewById(R.id.tv); 
     // Repeat for other views 

     tv.setText(track.getName()); 
     // Repeat for other views 

     return convertView; 
    } 
} 

從here，我已經試過這EndlessScrollListener：

class EndlessScrollListener implements AbsListView.OnScrollListener { 

    private int visibleThreshold = 5; 
    private int currentPage = 0; 
    private int previousTotal = 0; 
    private boolean loading = true; 

    public EndlessScrollListener() { 
    } 

    public EndlessScrollListener(int visibleThreshold) { 
     this.visibleThreshold = visibleThreshold; 
    } 

    @Override 
    public void onScroll(AbsListView view, int firstVisibleItem, 
         int visibleItemCount, int totalItemCount) { 
     if (loading) { 
      if (totalItemCount > previousTotal) { 
       loading = false; 
       previousTotal = totalItemCount; 
       currentPage++; 
      } 
     } 
     if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) { 
      // I load the next page of gigs using a background task, 
      // but you can call any function here. 
      new RecentTracksTask().execute(currentPage + 1); 
      loading = true; 
     } 
    } 

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

我試圖簡化代碼儘可能沒有刪除任何有用的東西，但我知道它仍然是有點長，可以通讀。

在片段的onCreateView中，我調用new RecentTracksTask().execute(1);，它將前15個項目成功加載到ListView中。當在ListView底部附近滾動時，整個內容將被替換爲第二頁，並且視圖返回到列表頂部。重複這只是將我移動到列表的頂部，仍然顯示第二頁。

• 如何獲取它，以便第n頁的項目插入列表底部而不是替換列表？
• 如何阻止它將視圖移動到列表頂部？

在此先感謝！

Answer 1

首先，擺脫EndlessScrollListener。然後，更新您的AsyncTask以獲取數據，將其附加到已在使用的適配器，並通知適配器數據集更改。最後，在您的適配器中，添加一個檢查是否到達列表的末尾並請求下一頁。然而，我應該警告你，如果你在最後一個視圖加載的時候滾動到最後一個視圖，你需要跟蹤你的異步任務，並防止它重新創建。

的AsyncTask

class RecentTracksTask extends AsyncTask<Integer, Void, Void> { 

    ArrayList<Track> recentTracks; 

    @Override 
    protected Void doInBackground(Integer... page) { 
     try { 
      // Get a page of 15 tracks 
      // Simplified - getPage accepts 'page' and 'limit' parameters and returns a Collection<Track> 
      recentTracks = new ArrayList<Track>(getPage(page[0], 15)); 

     } catch() {} 

     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 
     ListView listView = (ListView) getActivity().findViewById(R.id.listview); 
     ArrayAdapter adapter = (ArrayAdapter) listView.getAdapter(); 
     if(adapter == null) { 
      adapter = new TracksAdapter(getActivity(), recentTracks); 
      listView.setAdapter(adapter); 
     } else { 
      adapter.addAll(recentTracks); 
      adapter.notifyDataSetChanged(); 
     } 
    } 
} 

適配器：

class TracksAdapter extends ArrayAdapter<Track> { 
    private final Context context; 
    private final ArrayList<Track> tracks; 
    private int currentPage = 0; 

    public TracksAdapter(Context context, 
         ArrayList<Track> recentTrackArrayList) { 
     super(context, 0, recentTrackArrayList); 
     this.context = context; 
     this.tracks = recentTrackArrayList; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     if (convertView == null) { 
      LayoutInflater inflater = (LayoutInflater) context 
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      convertView = inflater.inflate(R.layout.list_item, 
        parent, false); 
     } 

     final Track track = tracks.get(position); 

     final TextView tv = (TextView) convertView 
       .findViewById(R.id.tv); 
     // Repeat for other views 

     tv.setText(track.getName()); 
     // Repeat for other views 

     //Check if we're at the end of the list 
     if(position == getCount() - 1) { 
      currentPage++; 
      new RecentTracksTask().execute(currentPage); 
     } 

     return convertView; 
    } 
}