Android ListView异步加载网络图片

package com.async.util;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;

//异步加载图片栈类
public class AsyncImageTask {
//缓存图片
private Map<String, Drawable> imageMap;

public AsyncImageTask() {
super();
this.imageMap = new HashMap<String, Drawable>();
}

// ID为记录标识,标识是那条记录iamge
public Drawable loadImage(final int id, final String imageUrl,
final ImageCallback callback) {
//查看缓存内是否已经加载过此图片
if (imageMap.containsKey(imageUrl)) {
Drawable drawable = imageMap.get(imageUrl);
if (drawable != null) {
return drawable;
}
}
//更新图片UI的消息队列
final Handler handler = new Handler() {
public void handleMessage(Message message) {
callback.imageLoaded((Drawable) message.obj, id);
}
};
//加载图片的线程
new Thread() {
@Override
public void run() {
super.run();
//加载图片
Drawable drawable = AsyncImageTask.loadImageByUrl(imageUrl);
//加入缓存集合中
imageMap.put(imageUrl, drawable);
//通知消息队列更新UI
Message message = handler.obtainMessage(0, drawable);
handler.sendMessage(message);
}
}.start();
return null;
}
//根据图片地址加载图片，并保存为Drawable
public static Drawable loadImageByUrl(String imageUrl) {

URL url = null;
InputStream inputStream = null;
try {
url = new URL(imageUrl);
inputStream = (InputStream) url.getContent();
return Drawable.createFromStream(inputStream, "src");
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (inputStream != null) {
inputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
//利用借口回调，更新图片UI
public interface ImageCallback {
public void imageLoaded(Drawable image, int id);
}
}

package com.alarm.adapter;

import java.util.List;

import com.alarm.activity.R;
import com.alarm.controls.AsyncImageTask;
import com.alarm.controls.AsyncImageTask.ImageCallback;
import com.alarm.model.Topic;

import android.content.Context;
import android.graphics.drawable.Drawable;
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 TopicsAdapter extends BaseAdapter {
private List<Topic> list;
private LayoutInflater inflater;
private ListView listView;
private AsyncImageTask imageTask;

public TopicsAdapter(ListView listView, Context c, List<Topic> list) {
super();
this.list = list;
this.listView = listView;
inflater = LayoutInflater.from(c);
imageTask = new AsyncImageTask();
}

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

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

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

@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = new ViewHolder();
if (convertView == null) {
convertView = inflater.inflate(R.layout.topic_item, null);
holder.mainBg = (ImageView) convertView.findViewById(R.id.main_bg);
holder.note = (TextView) convertView.findViewById(R.id.memo);
holder.name = (TextView) convertView.findViewById(R.id.name);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
// 标记图片视图，注意不能放在上面
holder.mainBg.setTag(position);
Topic topic = list.get(position);
//获取图片
Drawable drawable = imageTask.loadImage(position, topic.mainBg,
new ImageCallback() {
@Override
public void imageLoaded(Drawable image, int id) {
if (image != null) {
//重点，获取刚才标识的组件，并更新
ImageView mainBg = (ImageView) listView
.findViewWithTag(id);
if (mainBg != null) {
mainBg.setImageDrawable(image);
}
}
}
});
if (drawable != null) {
holder.mainBg.setImageDrawable(drawable);
} else {
holder.mainBg.setImageResource(R.color.main_bg);
}
holder.note.setText(topic.note);
holder.name.setText(topic.name);
return convertView;
}

class ViewHolder {
ImageView mainBg;
TextView note;
TextView name;
}

}