ListView异步加载网络图片

<uses-permission android:name="android.permission.INTERNET"/>

import java.util.LinkedList;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.widget.ListView;

import com.example.loadimages.R;
import com.lxw.adapter.ImageAdapter;
import com.lxw.bean.Picture;

public class MainActivity extends Activity {

    private ListView listview;
    private LinkedList<Picture> data;
    private ImageAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        loadData();
        listview = (ListView) findViewById(R.id.listview);
        adapter = new ImageAdapter(data, getLayoutInflater(), this);
        listview.setAdapter(adapter);
    }

    public void loadData() {
        if (data == null)
            data = new LinkedList<Picture>();
        for (int i = 0; i < URLS.length; i++) {
            data.add(new Picture(URLS[i]));
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    private static final String[] URLS = {
            "http://img5.imgtn.bdimg.com/it/u=1446812229,652623722&fm=21&gp=0.jpg",
            "http://img1.imgtn.bdimg.com/it/u=4011018736,2992079449&fm=21&gp=0.jpg",
            "http://img3.imgtn.bdimg.com/it/u=613517753,3662840626&fm=21&gp=0.jpg",
            "http://img4.duitang.com/uploads/item/201306/18/20130618235128_HyJNB.thumb.600_0.jpeg",
            "http://img4.imgtn.bdimg.com/it/u=572663234,2967721388&fm=21&gp=0.jpg",
            "http://img4.imgtn.bdimg.com/it/u=2456284265,2038282593&fm=21&gp=0.jpg",
            "http://img3.imgtn.bdimg.com/it/u=1628117601,1249996752&fm=21&gp=0.jpg",
            "http://lh5.ggpht.com/_mrb7w4gF8Ds/TCpetKSqM1I/AAAAAAAAD2c/Qef6Gsqf12Y/s144-c/_DSC4374%20copy.jpg",  
            "http://lh5.ggpht.com/_Z6tbBnE-swM/TB0CryLkiLI/AAAAAAAAVSo/n6B78hsDUz4/s144-c/_DSC3454.jpg",  
            "http://lh3.ggpht.com/_GEnSvSHk4iE/TDSfmyCfn0I/AAAAAAAAF8Y/cqmhEoxbwys/s144-c/_MG_3675.jpg",  
            "http://lh6.ggpht.com/_Nsxc889y6hY/TBp7jfx-cgI/AAAAAAAAHAg/Rr7jX44r2Gc/s144-c/IMGP9775a.jpg",  
            "http://lh3.ggpht.com/_lLj6go_T1CQ/TCD8PW09KBI/AAAAAAAAQdc/AqmOJ7eg5ig/s144-c/Juvenile%20Gannet%20despute.jpg",  
            "http://lh6.ggpht.com/_ZN5zQnkI67I/TCFFZaJHDnI/AAAAAAAABVk/YoUbDQHJRdo/s144-c/P9250508.JPG",  
            "http://lh4.ggpht.com/_XjNwVI0kmW8/TCOwNtzGheI/AAAAAAAAC84/SxFJhG7Scgo/s144-c/0014.jpg",  
            "http://lh6.ggpht.com/_lnDTHoDrJ_Y/TBvKsJ9qHtI/AAAAAAAAG6g/Zll2zGvrm9c/s144-c/000007.JPG",  
            "http://lh6.ggpht.com/_qvCl2efjxy0/TCIVI-TkuGI/AAAAAAAAOUY/vbk9MURsv48/s144-c/DSC_0844.JPG",  
            "http://lh4.ggpht.com/_4f1e_yo-zMQ/TCe5h9yN-TI/AAAAAAAAXqs/8X2fIjtKjmw/s144-c/IMG_1786.JPG",  
            "http://lh6.ggpht.com/_iFt5VZDjxkY/TB9rQyWnJ4I/AAAAAAAADpU/lP2iStizJz0/s144-c/DSCF1014.JPG",  
            "http://lh5.ggpht.com/_hepKlJWopDg/TB-_WXikaYI/AAAAAAAAElI/715k4NvBM4w/s144-c/IMG_0075.JPG",  
            "http://lh6.ggpht.com/_OfRSx6nn68g/TCzsQic_z3I/AAAAAAABOOI/5G4Kwzb2qhk/s144-c/EASTER%20ISLAND_Hanga%20Roa_31.5.08_46.JPG",  
            "http://lh6.ggpht.com/_ZGv_0FWPbTE/TB-_GLhqYBI/AAAAAAABVxs/cVEvQzt0ke4/s144-c/IMG_1288_hf.jpg",  
            "http://lh6.ggpht.com/_a29lGRJwo0E/TBqOK_tUKmI/AAAAAAAAVbw/UloKpjsKP3c/s144-c/31012332.jpg",  
            "http://lh3.ggpht.com/_55Lla4_ARA4/TB6xbyxxJ9I/AAAAAAABTWo/GKe24SwECns/s144-c/Bluebird%20049.JPG",  
            "http://lh3.ggpht.com/_iVnqmIBYi4Y/TCaOH6rRl1I/AAAAAAAA1qg/qeMerYQ6DYo/s144-c/Kwiat_100626_0016.jpg",  
            "http://lh6.ggpht.com/_QFsB_q7HFlo/TCItd_2oBkI/AAAAAAAAFsk/4lgJWweJ5N8/s144-c/3705226938_d6d66d6068_o.jpg",  
            "http://lh5.ggpht.com/_JTI0xxNrKFA/TBsKQ9uOGNI/AAAAAAAChQg/z8Exh32VVTA/s144-c/CRW_0015-composite.jpg",  
            "http://lh6.ggpht.com/_loGyjar4MMI/S-InVNkTR_I/AAAAAAAADJY/Fb5ifFNGD70/s144-c/Moving%20Rock.jpg",  
            "http://lh4.ggpht.com/_L7i4Tra_XRY/TBtxjScXLqI/AAAAAAAAE5o/ue15HuP8eWw/s144-c/opera%20house%20II.jpg",  
            "http://lh3.ggpht.com/_rfAz5DWHZYs/S9cstBTv1iI/AAAAAAAAeYA/EyZPUeLMQ98/s144-c/DSC_6425.jpg",  
            "http://lh6.ggpht.com/_iGI-XCxGLew/S-iYQWBEG-I/AAAAAAAACB8/JuFti4elptE/s144-c/norvig-polar-bear.jpg",  
            "http://lh3.ggpht.com/_M3slUPpIgmk/SlbnavqG1cI/AAAAAAAACvo/z6-CnXGma7E/s144-c/mf_003.jpg",  
            "http://lh4.ggpht.com/_loGyjar4MMI/S-InQvd_3hI/AAAAAAAADIw/dHvCFWfyHxQ/s144-c/Rainbokeh.jpg",  
            "http://lh4.ggpht.com/_yy6KdedPYp4/SB5rpK3Zv0I/AAAAAAAAOM8/mokl_yo2c9E/s144-c/Point%20Reyes%20road%20.jpg",  
            "http://lh5.ggpht.com/_6_dLVKawGJA/SMwq86HlAqI/AAAAAAAAG5U/q1gDNkmE5hI/s144-c/mobius-glow.jpg",  
            "http://lh3.ggpht.com/_QFsB_q7HFlo/TCItc19Jw3I/AAAAAAAAFs4/nPfiz5VGENk/s144-c/4551649039_852be0a952_o.jpg",  
            "http://lh6.ggpht.com/_TQY-Nm7P7Jc/TBpjA0ks2MI/AAAAAAAABcI/J6ViH98_poM/s144-c/IMG_6517.jpg",  
            "http://lh3.ggpht.com/_rfAz5DWHZYs/S9cLAeKuueI/AAAAAAAAeYU/E19G8DOlJRo/s144-c/DSC_4397_8_9_tonemapped2.jpg",  
            "http://lh4.ggpht.com/_TQY-Nm7P7Jc/TBpi6rKfFII/AAAAAAAABbg/79FOc0Dbq0c/s144-c/david_lee_sakura.jpg",  
            "http://lh3.ggpht.com/_TQY-Nm7P7Jc/TBpi8EJ4eDI/AAAAAAAABb0/AZ8Cw1GCaIs/s144-c/Hokkaido%20Swans.jpg",  
            "http://lh3.ggpht.com/_1aZMSFkxSJI/TCIjB6od89I/AAAAAAAACHM/CLWrkH0ziII/s144-c/079.jpg",  
            "http://lh5.ggpht.com/_loGyjar4MMI/S-InWuHkR9I/AAAAAAAADJE/wD-XdmF7yUQ/s144-c/Colorado%20River%20Sunset.jpg",  
            "http://lh3.ggpht.com/_0YSlK3HfZDQ/TCExCG1Zc3I/AAAAAAAAX1w/9oCH47V6uIQ/s144-c/3138923889_a7fa89cf94_o.jpg",  
            "http://lh6.ggpht.com/_K29ox9DWiaM/TAXe4Fi0xTI/AAAAAAAAVIY/zZA2Qqt2HG0/s144-c/IMG_7100.JPG",  
            "http://lh6.ggpht.com/_0YSlK3HfZDQ/TCEx16nJqpI/AAAAAAAAX1c/R5Vkzb8l7yo/s144-c/4235400281_34d87a1e0a_o.jpg",  
            "http://lh4.ggpht.com/_8zSk3OGcpP4/TBsOVXXnkTI/AAAAAAAAAEo/0AwEmuqvboo/s144-c/yosemite_forrest.jpg",  
            "http://lh4.ggpht.com/_6_dLVKawGJA/SLZToqXXVrI/AAAAAAAAG5k/7fPSz_ldN9w/s144-c/coastal-1.jpg",  
            "http://lh4.ggpht.com/_WW8gsdKXVXI/TBpVr9i6BxI/AAAAAAABhNg/KC8aAJ0wVyk/s144-c/IMG_6233_1_2-2.jpg",  
            "http://lh3.ggpht.com/_loGyjar4MMI/S-InS0tJJSI/AAAAAAAADHU/E8GQJ_qII58/s144-c/Windmills.jpg",  
            "http://lh4.ggpht.com/_loGyjar4MMI/S-InbXaME3I/AAAAAAAADHo/4gNYkbxemFM/s144-c/Frantic.jpg",  
            "http://lh5.ggpht.com/_loGyjar4MMI/S-InKAviXzI/AAAAAAAADHA/NkyP5Gge8eQ/s144-c/Rice%20Fields.jpg",  
            "http://lh3.ggpht.com/_loGyjar4MMI/S-InZA8YsZI/AAAAAAAADH8/csssVxalPcc/s144-c/Seahorse.jpg",  
            "http://lh3.ggpht.com/_syQa1hJRWGY/TBwkCHcq6aI/AAAAAAABBEg/R5KU1WWq59E/s144-c/Antelope.JPG",  
            "http://lh5.ggpht.com/_MoEPoevCLZc/S9fHzNgdKDI/AAAAAAAADwE/UAno6j5StAs/s144-c/c84_7083.jpg",  
            "http://lh4.ggpht.com/_DJGvVWd7IEc/TBpRsGjdAyI/AAAAAAAAFNw/rdvyRDgUD8A/s144-c/Free.jpg",  
            "http://lh6.ggpht.com/_iO97DXC99NY/TBwq3_kmp9I/AAAAAAABcz0/apq1ffo_MZo/s144-c/IMG_0682_cp.jpg",  
            "http://lh4.ggpht.com/_7V85eCJY_fg/TBpXudG4_PI/AAAAAAAAPEE/8cHJ7G84TkM/s144-c/20100530_120257_0273-Edit-2.jpg"};

}

package com.lxw.adapter;

import java.util.LinkedList;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;

import com.example.loadimages.R;
import com.lxw.bean.Picture;
import com.lxw.manager.BitmapManager;

public class ImageAdapter extends BaseAdapter {

    LinkedList<Picture> data = new LinkedList<Picture>();
    LayoutInflater inflator;
    Context context;

    public ImageAdapter(LinkedList<Picture> data, LayoutInflater inflator,
            Context context) {
        this.data = data;
        this.inflator = inflator;
        this.context = context;
    }

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

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        if (convertView == null) {
            convertView = inflator.inflate(R.layout.row, null);
            ImageView imageView = (ImageView) convertView
                    .findViewById(R.id.image);
            holder = new ViewHolder();
            holder.imageView = imageView;
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        Picture item = data.get(position);
        holder.imageView.setImageDrawable(this.context.getResources()
                .getDrawable(R.drawable.ic_launcher));

        BitmapManager.INSTANCE.loadBitmap(item.getImageUrl(), holder.imageView,
                300, 300);

        return convertView;
    }

    class ViewHolder {
        ImageView imageView;
    }
}

package com.lxw.manager;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import android.annotation.SuppressLint;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;

public enum BitmapManager {
    INSTANCE;

    private final Map<String, SoftReference<Bitmap>> cache;
    private final ExecutorService pool;
    private Map<ImageView, String> imageViews = Collections
            .synchronizedMap(new WeakHashMap<ImageView, String>());
    private Bitmap placeholder;

    BitmapManager() {
        cache = new HashMap<String, SoftReference<Bitmap>>();
        pool = Executors.newFixedThreadPool(5);
    }

    public void setPlaceholder(Bitmap bmp) {
        placeholder = bmp;
    }

    public Bitmap getBitmapFromCache(String url) {
        if (cache.containsKey(url)) {
            return cache.get(url).get();
        }

        return null;
    }

    @SuppressLint("HandlerLeak")
    public void queueJob(final String url, final ImageView imageView,
            final int width, final int height) {
        /* Create handler in UI thread. */
        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                String tag = imageViews.get(imageView);
                if (tag != null && tag.equals(url)) {
                    if (msg.obj != null) {
                        imageView.setImageBitmap((Bitmap) msg.obj);
                    } else {
                        imageView.setImageBitmap(placeholder);
                        Log.d(null, "fail " + url);
                    }
                }
            }
        };

        pool.submit(new Runnable() {
            @Override
            public void run() {
                final Bitmap bmp = downloadBitmap(url, width, height);
                Message message = Message.obtain();
                message.obj = bmp;
                Log.d("domn", "Item downloaded:");

                handler.sendMessage(message);
            }
        });
    }

    public void loadBitmap(final String url, final ImageView imageView,
            final int width, final int height) {
        imageViews.put(imageView, url);
        Bitmap bitmap = getBitmapFromCache(url);

        // check in UI thread, so no concurrency issues
        if (bitmap != null) {
            Log.d(null, "Item loaded from cache: " + url);
            imageView.setImageBitmap(bitmap);
        } else {
            imageView.setImageBitmap(placeholder);
            queueJob(url, imageView, width, height);
        }
    }

    private Bitmap downloadBitmap(String url, int width, int height) {
        try {
            Bitmap bitmap = BitmapFactory.decodeStream((InputStream) new URL(
                    url).getContent());
            bitmap = Bitmap.createScaledBitmap(bitmap, width, height, true);
            cache.put(url, new SoftReference<Bitmap>(bitmap));
            return bitmap;
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        Log.d("bitap", "null");
        return null;
    }
}

package com.lxw.bean;

public class Picture {
    private String imageUrl;
    
    public Picture(String imageUrl) {
        this.imageUrl = imageUrl;
    }
    public String getImageUrl() {
        return imageUrl;
    }
    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<ListView
android:id="@+id/listview"
android:layout_width="match_parent"
android:layout_height="match_parent" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/app_name" />

</LinearLayout>