Android程序开发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）

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(); } } }

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;
}
}

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;
}
}

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;
}
}