在底部滚动时,列表视图中的 LoadMore 会清除上一个项目 android?

LoadMore in listview clears previous item when scrolled at bottom android?

我正在使用 loadmore listview 来获取项目。最初我得到 20 个项目,displayed.But 问题是当我滚动到底部时它获取接下来的 20 个项目但前 20 个项目被清除。如何解决这个问题?这是代码。

 public class ActivityChatView extends ActivityBase implements
    OnLoadMoreListener {
private LoadMoreListView chatList;
private Intent intent;
private String expertName, chatId;
private int offset = 0;
ArrayList<History> chatHistoryList;
private AdapterChatView mAdapter;
private ProgressBar progressBar;
private TextView progressText;
private boolean isProgressNeeded = true;
private String rowId;

protected void setContentToLayout() {
    setContentView(R.layout.activity_chat_view);
    initChatListView();
    offset = 0;

}

private void initChatListView() {
    intent = getIntent();
    chatList = (LoadMoreListView) findViewById(R.id.list_chat_data);
    progressBar = (ProgressBar) findViewById(R.id.probar);
    progressText = (TextView) findViewById(R.id.loading_text);
    progressBar.setVisibility(View.VISIBLE);
    progressText.setVisibility(View.VISIBLE);
    chatList.setEmptyView(findViewById(android.R.id.empty));
    chatList.setOnLoadMoreListener(this);
    expertName = intent.getStringExtra(Constants.EXPERT_NAME);
    chatId = intent.getStringExtra(Constants.CHAT_ID);
    if (isProgressNeeded)
        progressBar.setVisibility(View.VISIBLE);
    progressText.setVisibility(View.VISIBLE);
    serviceCall(offset);
}
private void serviceCall(int offset) {
    startService(new Intent(ActivityChatView.this, ChatService.class)
            .setAction(Constants.CHAT_HISTORY)
            .putExtra(Constants.USER_ID, expertName)
            .putExtra(Constants.CHAT_ID, chatId)
            .putExtra(Constants.OFFSET, String.valueOf(offset)));
}

protected void onChatHistory(ArrayList<? extends Parcelable> arrayList) {
    ArrayList<History> listHistory = (ArrayList<History>) arrayList;
    chatHistoryList = new ArrayList<History>();
    for (int i = 0; i < listHistory.size(); i++) {
        History historyData = new History();
        historyData.setFromUser(listHistory.get(i).getFromUser());
        historyData.setMsgBody(listHistory.get(i).getMsgBody());
        historyData.setMsgTime(listHistory.get(i).getMsgTime());
        historyData.setRowId(listHistory.get(i).getRowId());
        historyData.setMsgId(listHistory.get(i).getMsgId());
        historyData.setToUser(listHistory.get(i).getToUser());
        chatHistoryList.add(historyData);
    }
    progressBar.setVisibility(View.GONE);
    progressText.setVisibility(View.GONE);
    setValuesInAdapter();
}
@Override
public void onLoadMore() {
    LogMessage.e("number", "number"+offset);
    serviceCall(offset);
}
private void setValuesInAdapter() {
    if (mAdapter == null) {
        mAdapter = new AdapterChatView(this, chatHistoryList);
        chatList.setAdapter(mAdapter);
    }
    mAdapter.setExpertData(chatHistoryList);
    mAdapter.notifyDataSetChanged();
    chatList.onLoadMoreComplete();
    History e = chatHistoryList.get(chatHistoryList.size() - 1);
    rowId= e.getRowId();
    LogMessage.e("rowId", rowId);
    offset = Integer.valueOf(rowId);
    if (chatHistoryList != null && !chatHistoryList.isEmpty()) {
        chatList.setVisibility(View.VISIBLE);
        chatList.getEmptyView().setVisibility(View.GONE);
    } else {
        chatList.getEmptyView().setVisibility(View.VISIBLE);
    }
}

}

  in adapter..
 //setExpertData.
 public void setExpertData(List<History> chatHistoryList) {
    this.mTempData = chatHistoryList;
}
protected void onChatHistory(ArrayList<? extends Parcelable> arrayList) {
    ArrayList<History> listHistory = (ArrayList<History>) arrayList;
    //chatHistoryList = new ArrayList<History>();// (Remove this line from here)
    for (int i = 0; i < listHistory.size(); i++) {
        History historyData = new History();
        historyData.setFromUser(listHistory.get(i).getFromUser());
        historyData.setMsgBody(listHistory.get(i).getMsgBody());
        historyData.setMsgTime(listHistory.get(i).getMsgTime());
        historyData.setRowId(listHistory.get(i).getRowId());
        historyData.setMsgId(listHistory.get(i).getMsgId());
        historyData.setToUser(listHistory.get(i).getToUser());
        chatHistoryList.add(historyData);
    }
    progressBar.setVisibility(View.GONE);
    progressText.setVisibility(View.GONE);
    setValuesInAdapter();
}

并把它带进来

private void initChatListView() {

chatHistoryList = new ArrayList<History>();
    intent = getIntent();
    chatList = (LoadMoreListView) findViewById(R.id.list_chat_data);
    progressBar = (ProgressBar) findViewById(R.id.probar);
    progressText = (TextView) findViewById(R.id.loading_text);
    progressBar.setVisibility(View.VISIBLE);
    progressText.setVisibility(View.VISIBLE);
    chatList.setEmptyView(findViewById(android.R.id.empty));
    chatList.setOnLoadMoreListener(this);
    expertName = intent.getStringExtra(Constants.EXPERT_NAME);
    chatId = intent.getStringExtra(Constants.CHAT_ID);
    if (isProgressNeeded)
        progressBar.setVisibility(View.VISIBLE);
    progressText.setVisibility(View.VISIBLE);
    serviceCall(offset);
}