android开发ListView+Json+异步网络图片加载+滚动翻页的例子（图片能缓存，图片不错乱）

例子中用于解析Json的Gson请自己Google下载

主Activity：

package COM.Example.Main;



import java.util.HashMap;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.List;

import java.util.Map;



import COM.Example.Main.R;

import COM.Example.Main.stringGetJson.User;

import android.app.Activity;

import android.app.ListActivity;

import android.os.AsyncTask;

import android.os.Bundle;

import android.view.Gravity;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.AbsListView;

import android.widget.AbsListView.OnScrollListener;

import android.widget.ArrayAdapter;

import android.widget.ImageView;

import android.widget.LinearLayout;

import android.widget.ListView;

import android.widget.ProgressBar;

import android.widget.TextView;



public class stringListActivity extends ListActivity {



    private MyAdapter mMyAdapter;

    private LinkedList<User> users = null;

    // 当前Activity中的ListView

    ListView listView = null;

    int lastItem = 0;

    LinearLayout loadingLayout = null;



    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.foodlistactivity);



        listView = getListView();

        setLoadingLayout();

        new readTask().execute(null);

    }



    private final class MyAdapter extends ArrayAdapter<User> {

        public MyAdapter(Activity activity, List<User> newsList) {

            super(activity, 0, newsList);

        }



        private Map<Integer, View> viewMap = new HashMap<Integer, View>();



        @Override

        public View getView(int position, View convertView, ViewGroup parent) {

            ViewHolder holder;



            View rowView = this.viewMap.get(position);



            if (rowView == null) {

                User user = users.get(position);

                LayoutInflater inflater = ((Activity) this.getContext())

                        .getLayoutInflater();

                holder = new ViewHolder();

                rowView = inflater

                        .inflate(R.layout.foodlistactivity_item, null);

                holder.mNameText = (TextView) rowView

                        .findViewById(R.id.foodItemUsername);

                holder.mPhoto = (ImageView) rowView

                        .findViewById(R.id.foodItemPic);

                rowView.setTag(holder);



                holder.mNameText.setText(user.Name);



                if (!holder.mPhoto.isDrawingCacheEnabled()) {

                    holder.mPhoto.setTag(user.Pic);

                    new downImageTask().execute(holder.mPhoto);

                    holder.mPhoto.setDrawingCacheEnabled(true);

                }

                viewMap.put(position, rowView);

            } else {

                holder = (ViewHolder) rowView.getTag();

            }



            return rowView;

        }



        public class ViewHolder {

            public TextView mNameText;

            public ImageView mPhoto;

        }



    }



    public void setLoadingLayout() {

        LinearLayout layout = new LinearLayout(this);

        layout.setOrientation(LinearLayout.HORIZONTAL);

        ProgressBar progressBar = new ProgressBar(this);

        progressBar.setPadding(0, 0, 15, 0);

        layout.addView(progressBar);

        TextView textView = new TextView(this);

        textView.setText("加载中...");

        textView.setGravity(Gravity.CENTER_VERTICAL);

        layout.addView(textView);

        layout.setGravity(Gravity.CENTER);

        loadingLayout = new LinearLayout(this);

        loadingLayout.addView(layout);

        loadingLayout.setGravity(Gravity.CENTER);

    }

    

    private class scrollListener implements OnScrollListener {

        @Override

        public void onScroll(AbsListView view, int firstVisibleItem,

                int visibleItemCount, int totalItemCount) {

            // 当listView中没有数据，或者数据超过100条，或者不是10的整数倍（即数据不足）时隐藏“更多”并取消onScroll事件的绑定

            if (mMyAdapter.getCount() >= 100 || mMyAdapter.getCount() % 10 > 0

                    || mMyAdapter.getCount() == 0) {

                listView.removeFooterView(loadingLayout);

                listView.setOnScrollListener(null);

            }

            lastItem = firstVisibleItem + visibleItemCount - 1;// 这里减一是因为有FootView

        }



        @Override

        public void onScrollStateChanged(AbsListView view, int scrollState) {

            if (lastItem == mMyAdapter.getCount()

                    && scrollState == OnScrollListener.SCROLL_STATE_IDLE) {

                // 进行翻页操作

                new scrollTask().execute(null);

            }



        }

    }

    

    public class readTask extends AsyncTask<Object, Void, Void> {

    

        @Override

        protected Void doInBackground(Object... arg0) {

            users = new stringGetJson().getJson();

            return null;

        }



        @Override

        protected void onPostExecute(Void result) {

            listView.addFooterView(loadingLayout);

            

            mMyAdapter = new MyAdapter(stringListActivity.this, users);

            setListAdapter(mMyAdapter);

            listView.setOnScrollListener(new scrollListener());

        }

    }



    public class scrollTask extends AsyncTask<Object, Void, Void> {

        

        @Override

        protected Void doInBackground(Object... arg0) {

            for (Iterator iterator = new stringGetJson().getJson()

                    .iterator(); iterator.hasNext();) {

                User user = (User) iterator.next();

                users.add(user);

            }

            return null;

        }



        @Override

        protected void onPostExecute(Void result) {

            mMyAdapter.notifyDataSetChanged();

        }

    }

}

Json数据来源（这里的例子中把json字符串直接写在代码中了，实际项目中需要改成从网络读取，例子中已经使用了多线程）：

package COM.Example.Main;



import java.lang.reflect.Type;

import java.util.Iterator;

import java.util.LinkedList;



import android.database.MatrixCursor;

import android.widget.ListView;

import android.widget.TextView;



import com.google.gson.Gson;

import com.google.gson.reflect.TypeToken;

public class stringGetJson {

    

    // 设置临时ID，在项目中将被现实的id取代

    private int id = 0;

    

    public stringGetJson() {

        super();

    }



    //通过getJson方法从Json字符串获取User的列表

    public LinkedList<User> getJson() {

        String jsonData = "[{\"Name\":\"xinuxForJson1\",\"Pic\":\"http://www.qqjay.com/uploads/110414/1_234626_5.jpg\"},{\"Name\":\"xinuxForJson2\",\"Pic\":\"http://www.qqjay.com/uploads/110414/1_234626_3.jpg\"},{\"Name\":\"xinuxForJson3\",\"Pic\":\"http://www.qqjay.com/uploads/110414/1_234626_4.jpg\"},{\"Name\":\"xinuxForJson4\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/8.jpg\"},{\"Name\":\"xinuxForJson5\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/10.jpg\"},{\"Name\":\"xinuxForJson6\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/7.jpg\"},{\"Name\":\"xinuxForJson7\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/11.jpg\"},{\"Name\":\"xinuxForJson8\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/12.jpg\"},{\"Name\":\"xinuxForJson9\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/9.jpg\"},{\"Name\":\"xinuxForJson10\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian/7.jpg\"}]";

        Type listType = new TypeToken<LinkedList<User>>() {}.getType();

        Gson gson = new Gson();

        LinkedList<User> users = gson.fromJson(jsonData, listType);

        return users;

    }



    //为getJson提供了数据实体类

    final static class User {

        public String Name;

        public String Pic;

    }

}

图片下载AsyncTask

package COM.Example.Main;

import COM.Example.FunctionUtility.Download;
import android.graphics.Bitmap;
import android.os.AsyncTask;
import android.widget.ImageView;

public class downImageTask extends AsyncTask<ImageView, Void, Bitmap> {
    
    ImageView gView = null;
    @Override
    protected Bitmap doInBackground(ImageView... arg0) {
        gView = (ImageView)arg0[0];
        return Download.getBitmapFromUrl(gView.getTag().toString());
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        if(result != null){
        this.gView.setImageBitmap(result);
        }
        this.gView = null;
    }
}

网络图片下载类：

package COM.Example.FunctionUtility;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class Download {
    public static Bitmap getBitmapFromUrl(String imgUrl) {
        URL url;
        Bitmap bitmap = null;
        try {
            url = new URL(imgUrl);
            InputStream is = url.openConnection().getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is);
            bitmap = BitmapFactory.decodeStream(bis);
            bis.close();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return bitmap;
    }
}