android 异步回调加载网络图片

在做应用的时候很多时候都会去从网络加载图片，而且还要做各种各样的加载效果。比如，加载图片的时候在图片上显示loading的图片，图片加载完成时loading消失，加载失败又有相应的处理。如果处理不好就会很麻烦，下面总结了一个轻量级的从网络加载图片方法。

import java.io.File;

import java.io.IOException;

import java.net.HttpURLConnection;

import java.net.MalformedURLException;

import java.net.URL;



import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.os.Handler;

import android.os.Message;



public class Utils

{



    /**

     * 加载图片

     * @param url 图片的url

     * @param listener 回调监听器

     */

    public void loadImage(final String url, final OnLoadImageListener listener)

    {

        if (null == url || null == listener)

        {

            return;

        }

        

        final Handler handler = new Handler()

        {

            public void handleMessage(Message msg)

            {

                listener.onLoadImage((Bitmap) msg.obj, url);

            }

        };

        

        // 之前根据url写入本地缓存的路径

        String path = "";

        File file = new File(path);

        if (file.exists())

        {

            Bitmap bm = BitmapFactory.decodeFile(path);

            sendMessage(handler, bm);

            return;

        }



        new Thread(new Runnable()

        {

            public void run()

            {

                try

                {

                    // 网络加载图片，还可以加入延迟(time out)条件

                    URL u = new URL(url);

                    HttpURLConnection httpConnection = (HttpURLConnection) u.openConnection();

                    if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK)

                    {

                        Bitmap bm = BitmapFactory.decodeStream(httpConnection.getInputStream());

                        sendMessage(handler, bm);

                        // 同时对图片进行缓存...

                        return;

                    }

                    

                    // 没有请求到图片

                    sendMessage(handler, null);

                } catch (MalformedURLException e)

                {

                    sendMessage(handler, null);

                } catch (IOException e)

                {

                    sendMessage(handler, null);

                }

            }

        }).start();

            

    }

    

    /**

     * 向handler发送处理的消息

     * @param handler

     * @param bm

     */

    private void sendMessage(Handler handler, Bitmap bm)

    {

        Message msg = handler.obtainMessage();

        msg.obj = bm;

        handler.sendMessage(msg);

    }

    

    /**

     * 加载图片时的回调

     *

     */

    public interface OnLoadImageListener

    {

        public void onLoadImage(Bitmap bm, String imageUrl);

    }

}



此例中用到了Handler，从而不需要用到AsyncTask，AsyncTask感觉使用起来很麻烦，而且貌似还有延迟。这样做的话可以直接在回调里面做设置图片处理，而不必要担心是不是UI线程。如下：



new Utils().loadImage("图片链接", new OnLoadImageListener()

        {

            @Override

            public void onLoadImage(Bitmap bm, String imageUrl)

            {

                if (null == bm)

                {

                    imageView.setImageResource(R.drawable.default_img);

                }

                else

                {

                    imageView.setBitmapImage(bm);

                }

            }

            

        });


来自： http://www.2cto.com/kf/201110/107333.html