添加notifyDatesetChanged()后滑动卡到一半，既不能上划也不能下滑。请教，谢谢！

package com.example.android_listview;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import android.os.Build;

public class MainActivity extends Activity implements OnItemClickListener,OnScrollListener{
    private ListView listView;
    private ArrayAdapter<String>arr_adapter;
    private SimpleAdapter simp_adapter;
    private List<Map<String,Object>>dataList;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        listView=(ListView)findViewById(R.id.listView);
        String[]arr_data={"imook1","imook2","imook3","imook4"};
        dataList=new ArrayList<Map<String,Object>>();
        arr_adapter=new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arr_data);
        simp_adapter=new SimpleAdapter(this,getData(),R.layout.item,new String[]{"pic","text"},new int[]{R.id.pic,R.id.text});
        listView.setAdapter(simp_adapter);
        listView.setOnItemClickListener(this);
        listView.setOnScrollListener(this);
    }

private List<Map<String,Object>> getData()
{
 for(int i=0;i<20;i++)
 {
  Map<String,Object>map=new HashMap<String, Object>();
  map.put("pic",R.drawable.ic_launcher);
  map.put("text","imook"+i);
  dataList.add(map);
 }
 return dataList;
}

@Override
public void onScroll(AbsListView view, int scrollState, int arg2, int arg3) {
 // TODO Auto-generated method stub
 switch(scrollState)
 {
 case SCROLL_STATE_FLING:
  Log.i("Main","用户在手指离开屏幕之前，由于用力滑了一下，视图仍能继续滑动");
  Map<String,Object>map=new HashMap<String, Object>();
  map.put("pic",R.drawable.ic_launcher);
  map.put("text", "增加项");
  dataList.add(map);
  simp_adapter.notifyDataSetChanged();
  break;
 case SCROLL_STATE_IDLE:
  Log.i("Main","视图已经停止滑动");
  break;
 case SCROLL_STATE_TOUCH_SCROLL:
  Log.i("Main", "手指没有离开屏幕");
  break;
 }
}

@Override
public void onScrollStateChanged(AbsListView arg0, int arg1) {
 // TODO Auto-generated method stub
 
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
 // TODO Auto-generated method stub
 String text=listView.getItemIdAtPosition(position)+"";
 Toast.makeText(this, "position="+position+" text="+text, Toast.LENGTH_SHORT).show();
}
 
}