会话列表视图CursorAdapter pull listview加载更多内容

Question

目前我正在使用CursorAdapter进行聊天应用的聊天列表视图。我从SQLite填充了最新的20个聊天记录作为我的列表，当我像其他聊天应用程序一样滚动到顶部时，我想加载早期的聊天记录。怎么做到这一点？我应该使用CursorAdapter吗？或者进行另一个查询然后在滚动到列表视图顶部时合并另一个光标？

这是我的CursorAdapter代码，请提供帮助并提出建议。

public class ChatViewAdapter extends CursorAdapter{

private static final int MSG_TIME_SHOW_DELAY = 300000;

private String mUser;
private Context mContext;
private XmppBinder mXmppBinder;
private boolean mIsMultChat;
private LayoutInflater mInflater;

private Map<String, SoftReference<XmppVcard>> mVcards;
private Map<String, SoftReference<Bitmap>> mCache;

private View.OnClickListener mResendClickListener;
private View.OnClickListener mOnImageClickListener;
private View.OnClickListener mOnAudioClickListener;

private Handler mHandler;

public ChatViewAdapter(Context context,Cursor cursor,XmppBinder xmppBinder,String currentUser){
    super(context,cursor,true);
    mContext = context;
    mInflater = LayoutInflater.from(context);
    mUser = currentUser;
    mXmppBinder = xmppBinder;
    mCache = new HashMap<String, SoftReference<Bitmap>>();
    mVcards =  new HashMap<String, SoftReference<XmppVcard>>();
}


public void setOnImageClickListener(View.OnClickListener listener){
    mOnImageClickListener = listener;
}

public void setOnAudioClickListener(View.OnClickListener listener){
    mOnAudioClickListener = listener;
}

private int transfer(int position) {
    return getCount() - position - 1;
}

@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    return super.getDropDownView(transfer(position), convertView, parent);
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    position = transfer(position);
    if (position < 0 || position > getCursor().getCount() - 1) {
        return null;
    }
    return super.getItem(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return super.getItemId(transfer(position));
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    return super.getView(transfer(position), convertView, parent);
}

public void setResendClickListener(View.OnClickListener listener) {
    mResendClickListener = listener;
}

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
    View convertView = mInflater.inflate(R.layout.list_item_chat_msg,
            null);

    ViewHolder viewHolder = new ViewHolder();

    viewHolder.systemTip = (TextView) convertView
            .findViewById(R.id.chat_item_system_msg);

    viewHolder.leftView = convertView.findViewById(R.id.chat_item_left_view);
    viewHolder.leftAvartar = (HexagonImageView)convertView.findViewById(R.id.chat_item_from_avatar);
    viewHolder.leftMsgTxt = (TextView)convertView.findViewById(R.id.chat_msg_from_text);
    viewHolder.leftMsgImg = (AspectRatioMaskImageView)convertView.findViewById(R.id.chat_msg_from_image);

    viewHolder.rightView = convertView.findViewById(R.id.chat_item_right_view);
    viewHolder.rightAvartar = (HexagonImageView)convertView.findViewById(R.id.chat_item_to_avatar);
    viewHolder.rightMsgTxt = (TextView)convertView.findViewById(R.id.chat_msg_to_text);
    viewHolder.rightMsgImg = (AspectRatioMaskImageView)convertView.findViewById(R.id.chat_msg_to_image);

    convertView.setTag(viewHolder);
    return convertView;
}

@Override
public void bindView(View view, Context context, Cursor cursor) {
    ViewHolder viewHolder = (ViewHolder)view.getTag();
    if (viewHolder!=null){
        final String messageOwner = cursor.getString(cursor.getColumnIndex(MsgManager.MsgColumns.SENDER));
        boolean isComMsg = !messageOwner.startsWith(mUser);

        long date = cursor.getLong(cursor.getColumnIndex(MsgManager.MsgColumns.CREATE_DATE));
        viewHolder.systemTip.setText(DateFormat.format(
                "yyyy-MM-dd hh:mm:ss", new Date(date)));
        viewHolder.systemTip.setVisibility(View.GONE);

        int position = cursor.getPosition();

        Cursor nextCursor = (Cursor)getItem(cursor.getCount()-cursor.getPosition()-2);
        if (nextCursor!=null){
            long date2 = cursor.getLong(cursor
                    .getColumnIndex(MsgManager.MsgColumns.CREATE_DATE));
            if (Math.abs(date2 - date) > MSG_TIME_SHOW_DELAY) {
                viewHolder.systemTip.setVisibility(View.VISIBLE);
            }
        }

        cursor.moveToPosition(position);

        if (cursor.getPosition()==cursor.getPosition()-1){
            viewHolder.systemTip.setVisibility(View.VISIBLE);
        }

        String content  = cursor.getString(cursor.getColumnIndex(MsgManager.MsgColumns.CONTENT));
        HushLog.getInstance().i("msg %s",content);

        ChatMessage message= ChatMessage.fromString(content);

        TextView userTextView =null;
        HexagonImageView userImageView=null;
        if (isComMsg){
            viewHolder.rightView.setVisibility(View.GONE);
            viewHolder.leftView.setVisibility(View.VISIBLE);

            userImageView = viewHolder.leftAvartar;
            dealMsg(cursor.getInt(0),
                    viewHolder.leftMsgTxt,
                    viewHolder.leftMsgImg,
                    message,
                    isComMsg);

        } else {
            viewHolder.rightView.setVisibility(View.VISIBLE);
            viewHolder.leftView.setVisibility(View.GONE);

            userImageView = viewHolder.rightAvartar;
            dealMsg(cursor.getInt(0),
                    viewHolder.rightMsgTxt,
                    viewHolder.rightMsgImg,
                    message,
                    isComMsg);
        }

        final HexagonImageView imgView = userImageView;
        SoftReference<XmppVcard> softReference = mVcards.get(messageOwner);
        if (softReference!=null && softReference.get()!=null){
            XmppVcard vcard = softReference.get();
            if (vcard.getGender().equals("M")){
                userImageView.setBorderColor(Color.BLUE);
            }
        } else {
            mXmppBinder.execute(new Runnable() {
                @Override
                public void run() {
                    final XmppVcard vcard = new XmppVcard(mXmppBinder.getServiceContext());
                    vcard.load(mXmppBinder.getXmppConnection(),messageOwner);
                    mVcards.put(messageOwner, new SoftReference<XmppVcard>(vcard));
                    if (vcard.getGender().equals("M") && imgView!=null){
                        imgView.setBorderColor(Color.BLUE);
                    }
                }
            });
        }
        userImageView.setImageResource(R.drawable.default_avatar);
        AsyncImageLoader.loadBitmapFromStore(messageOwner,new ImageLoaderListener() {
            @Override
            public void onImageLoaded(String url, Bitmap bitmap) {
                imgView.setImageBitmap(bitmap);
            }
        });
    }
}

private void dealMsg(int id,
                     TextView bodyTextView,
                     AspectRatioMaskImageView bodyImageView,
                     ChatMessage message,
                     boolean isComMsg){
    String content = message.getBody();
    ChatMessage.MsgType msgType = message.getType();

    bodyTextView.setOnClickListener(null);
    bodyTextView.setVisibility(View.GONE);
    bodyImageView.setVisibility(View.GONE);

    if (ChatMessage.MsgType.TEXT.equals(msgType)){
        bodyTextView.setVisibility(View.VISIBLE);
        bodyImageView.setVisibility(View.GONE);
        bodyTextView.setText(content);
    } else if (ChatMessage.MsgType.IMAGE.equals(msgType)){
        bodyTextView.setVisibility(View.GONE);
        bodyImageView.setVisibility(View.VISIBLE);
        String filePath = message.getBody();

    } else if (ChatMessage.MsgType.AUDIO.equals(msgType)){
        bodyTextView.setVisibility(View.VISIBLE);
        bodyImageView.setVisibility(View.GONE);
        try {
            String audioPath = message.getAudioPath();
            String  duration = message.getAudioDuration();
            bodyTextView.setText(duration+"\"");

        } catch (Exception e){

        }
    }
}

private class ViewHolder {
    TextView systemTip;

    View leftView;
    HexagonImageView leftAvartar;
    TextView leftMsgTxt;
    AspectRatioMaskImageView leftMsgImg;

    View rightView;
    HexagonImageView rightAvartar;
    TextView rightMsgTxt;
    AspectRatioMaskImageView rightMsgImg;

}
}