就最后一个图片一直在切换不同的图片

相关代码：

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
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;

import com.example.zuoye12.util.Msg;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MyAdapter extends BaseAdapter {
    List<Msg> mLessonInfos;
    private Context mContext;
    Bitmap bitmapc=null;
    ViewHolder  viewHolder;
    public MyAdapter(Context context,List<Msg> infos) {
        mLessonInfos=infos;
        mContext=context;
    }

    @Override
    public int getCount() {
        return mLessonInfos.size();
    }

    @Override
    public Object getItem(int position) {
        return mLessonInfos.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
//        viewHolder=new ViewHolder();
        if(convertView==null){
                        viewHolder = new ViewHolder();
            convertView = LayoutInflater.from(mContext).inflate(R.layout.item, parent, false);

            viewHolder.name = convertView.findViewById(R.id.name);
            viewHolder.img=convertView.findViewById(R.id.img);
            viewHolder.count = convertView.findViewById(R.id.count);
            viewHolder.price = convertView.findViewById(R.id.price);
            viewHolder.action = convertView.findViewById(R.id.description);
            viewHolder.action = convertView.findViewById(R.id.action);

            convertView.setTag(viewHolder);
        }else{
            viewHolder= (ViewHolder) convertView.getTag();
        }



        String url=mLessonInfos.get(position).getImageView();
        RequestDataAsyncTaskSecond taskSecond;
        new RequestDataAsyncTaskSecond().execute(url);
        viewHolder.name.setText(mLessonInfos.get(position).getName());
//        viewHolder.context.setText(mLessonInfos.get(position).getDescription());
        viewHolder.price.setText(mLessonInfos.get(position).getPrice());
        viewHolder.price.setText(mLessonInfos.get(position).getAction());
        viewHolder.action.setText(mLessonInfos.get(position).getCount());
        return convertView;
    }
    public class ViewHolder{
        public ImageView img;
        public TextView name;
        public TextView price;
        public TextView context;

        public TextView count;
        public TextView action;
    }
    public class RequestDataAsyncTaskSecond extends AsyncTask<String,Void,Bitmap> {
        String str=null;
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            //
        }

        protected Bitmap doInBackground(String...  path) {
            str=path[0];
            try {
                URL url = new URL(str);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setConnectTimeout(5000);
                conn.setRequestMethod("GET");
                if (conn.getResponseCode() == 200) {
                    InputStream inputStream = conn.getInputStream();
                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                    return bitmap;
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return null;
        }
        protected void onPostExecute(Bitmap bitmap) {
            viewHolder.img.setImageBitmap(bitmap);
            notifyDataSetChanged();

        }

    }

}

相关截图：

问题描述：

就最后一个图片一直在切换不同的图片