添加notifyDatesetChanged()后滑動卡到一半，既不能上劃也不能下滑。請教，謝謝！

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","用戶在手指離開屏幕之前，由于用力滑了一下，視圖仍能繼續滑動");
??Map<String,Object>map=new HashMap<String, Object>();
??map.put("pic",R.drawable.ic_launcher);
??map.put("text", "增加項");
??dataList.add(map);
??simp_adapter.notifyDataSetChanged();
??break;
?case SCROLL_STATE_IDLE:
??Log.i("Main","視圖已經停止滑動");
??break;
?case SCROLL_STATE_TOUCH_SCROLL:
??Log.i("Main", "手指沒有離開屏幕");
??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();
}
?
}