如何实现带照片缩略图的Listview

ackage com.demo;
 
import java.util.ArrayList;
 
import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.provider.MediaStore;
import android.provider.MediaStore.Images;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
 
public class PictureActivity extends Activity{ 
    private ListView picturefiles = null;
    private Cursor cursor;
    private ArrayList<PictureInfo> pictureList = new ArrayList<PictureActivity.PictureInfo>();
     
    private static final String[] STORE_IMAGES = {
        MediaStore.Images.Media.DATA,
        MediaStore.Images.Media.MIME_TYPE,
        MediaStore.Images.Media.DISPLAY_NAME,
        MediaStore.Images.Media._ID
    };
     
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.picture);
        showimage();
        // 单击显示图片
        //picturefiles.setOnItemClickListener(new ShowItemImageOnClickListener());
    }
     
    public void showimage(){
        picturefiles = (ListView)findViewById(R.id.picture_list);
        cursor = this.managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, STORE_IMAGES, null, null, null);
        while(cursor.moveToNext()){
            PictureInfo info = new PictureInfo();
             
            info.filePath = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA));
            info.mimeType = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Media.MIME_TYPE));
            info.title = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DISPLAY_NAME));
             
            //获取当前Picture对应的Id，然后根据该ID获取其Thumb
            int id = cursor.getInt(cursor.getColumnIndexOrThrow(MediaStore.Images.Media._ID));
            /*if(info.bitmap!=null&&!info.bitmap.isRecycled())
            {
                info.bitmap.recycle();
            }*/
            BitmapFactory.Options options=new BitmapFactory.Options();
            options.inDither=false;
            options.inPreferredConfig=Bitmap.Config.RGB_565;
            info.bitmap=MediaStore.Images.Thumbnails.getThumbnail(getContentResolver(), id,  Images.Thumbnails.MICRO_KIND, options); 
            //然后将其加入到pictureList
            pictureList.add(info);
        }
        System.out.println(pictureList.size());
        //然后需要设置ListView的Adapter了，使用我们自定义的Adatper
        PictureAdapter adapter = new PictureAdapter(this);
        picturefiles=(ListView)findViewById(R.id.picture_list);
        picturefiles.setAdapter(adapter);
    }
     
    class PictureInfo{
        String filePath;
        String mimeType;
        Bitmap bitmap;
        String title;
    }
     
    class ViewHolder{
        ImageView thumbImage;
        TextView titleText;
    }
     
    /**
     * 定义一个Adapter来显示缩略图和视频title信息
     * @author Administrator
     *
     */
    private class PictureAdapter extends BaseAdapter{
         
        private Context mContext;
        private LayoutInflater inflater;
         
        public PictureAdapter(Context context){
            this.mContext = context;
            this.inflater = LayoutInflater.from(context); 
            this.inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);  
        }
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return pictureList.size();
        }
        @Override
        public Object getItem(int p) {
            // TODO Auto-generated method stub
            return pictureList.get(p);
        }
        @Override
        public long getItemId(int p) {
            // TODO Auto-generated method stub
            return p;
        }
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder ;
            if(convertView == null){
                holder = new ViewHolder();
                convertView = inflater.inflate(R.layout.line, null);
                holder.thumbImage = (ImageView)convertView.findViewById(R.id.icon);
                holder.titleText = (TextView)convertView.findViewById(R.id.file_name);
                convertView.setTag(holder);
            }else{
                holder = (ViewHolder)convertView.getTag();
            }
             
            //显示信息
            holder.titleText.setText(pictureList.get(position).title);
            if(pictureList.get(position).bitmap != null){
                holder.thumbImage.setImageBitmap(pictureList.get(position).bitmap);
            }
            return convertView;
        }       
    }
}