列表视图setOnScrollListener保留返回到顶看

我已经列表视图与setOnScrollListener载更多的数据式，我使用际关获得手机中。 和java是10页，每页。 问题是当滚动到了底部，滚动其后总是回到顶部后，更多的数据显示(载入)，喜欢的活动是重新启动。

因此如何做出的滚动留在位置，而不返回到顶端?

代码

    listView.setOnScrollListener(new AbsListView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(AbsListView view, int scrollState) {
    
                }
    
                @Override
                public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                    if (firstVisibleItem+visibleItemCount == totalItemCount && totalItemCount!=0){
                        nextpage = nextpage + 1;
                        new getJSON().execute();
                    }
                }
            });

private class getJSON extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            footer.setVisibility(View.VISIBLE);
            pDialog = new ProgressDialog(PoActivity.this);
            pDialog.setMessage("Please Wait...");
            pDialog.setCancelable(false);
            pDialog.show();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            Handler handler = new Handler();

            String po = handler.makeServiceCall(url + "?page=" + nextpage);

            if (po != null){
                try {
                    JSONObject obj = new JSONObject(po);
                    JSONArray objArray = obj.getJSONArray("data");
                    for (int i = 0; i < objArray.length(); i++){
                        JSONObject data = objArray.getJSONObject(i);
                        String employee = data.getString("name");
                        String status = data.getString("status");


                        HashMap<String, String> datarow = new HashMap<>();

                        datarow.put("emp", employee);
                        datarow.put("status", status);

                        polist.add(datarow);

                    }
                }catch (final JSONException e){
                    Log.e(TAG, "Json parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getApplicationContext(), "Json parsing error: " + e.getMessage(), Toast.LENGTH_SHORT).show();
                        }
                    });
                }
            }else {
                Log.e(TAG,"Couldn't get json from server");
                endpage = 0;
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(), "Couldn't get json from server. check logcat", Toast.LENGTH_SHORT).show();
                    }
                });
            }

            pDialog.dismiss();
            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            pDialog.dismiss();
            footer.setVisibility(View.GONE);

            listAdapter = new SimpleAdapter(PoActivity.this, polist,
                    R.layout.po_row, new String[]{"emp", "status"},
                    new int[]{R.id.name, R.id.status});

            listView.setAdapter(listAdapter);    
        }
    }