我建议使用开源仪器Universal Image Loader。它最初基于Fedor Vlasov的项目LazyList，此后得到了极大的改进。

多线程图像加载可以广泛调整ImageLoader的配置（线程执行器、下载器、解码器、内存和磁盘缓存、显示图像选项等）可以在内存和/或设备的文件系统（或SD卡）中缓存图像“聆听”加载过程的可能性可以使用单独的选项自定义每个显示图像通话小工具支持Android 2.0+支持

我这样做的方式是启动一个线程，在后台下载图像，并为每个列表项传递一个回调。当图像下载完成后，它将调用回调，以更新列表项的视图。

然而，当您回收视图时，这种方法不太有效。

我写了一篇教程，解释如何在列表视图中延迟加载图像。我详细讨论了回收和并发的问题。我还使用固定线程池来防止产生大量线程。

在Listview教程中延迟加载图像

以下是我创建的用于保存应用程序当前显示的图像的内容。请注意，这里使用的“Log”对象是我对Android中最终Log类的自定义包装。

package com.wilson.android.library;

/*
 Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
*/
import java.io.IOException;

public class DrawableManager {
    private final Map<String, Drawable> drawableMap;

    public DrawableManager() {
        drawableMap = new HashMap<String, Drawable>();
    }

    public Drawable fetchDrawable(String urlString) {
        if (drawableMap.containsKey(urlString)) {
            return drawableMap.get(urlString);
        }

        Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
        try {
            InputStream is = fetch(urlString);
            Drawable drawable = Drawable.createFromStream(is, "src");


            if (drawable != null) {
                drawableMap.put(urlString, drawable);
                Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
                        + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
                        + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
            } else {
              Log.w(this.getClass().getSimpleName(), "could not get thumbnail");
            }

            return drawable;
        } catch (MalformedURLException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        } catch (IOException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        }
    }

    public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {
        if (drawableMap.containsKey(urlString)) {
            imageView.setImageDrawable(drawableMap.get(urlString));
        }

        final Handler handler = new Handler(Looper.getMainLooper()) {
            @Override
            public void handleMessage(Message message) {
                imageView.setImageDrawable((Drawable) message.obj);
            }
        };

        Thread thread = new Thread() {
            @Override
            public void run() {
                //TODO : set imageView to a "pending" image
                Drawable drawable = fetchDrawable(urlString);
                Message message = handler.obtainMessage(1, drawable);
                handler.sendMessage(message);
            }
        };
        thread.start();
    }

    private InputStream fetch(String urlString) throws MalformedURLException, IOException {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet request = new HttpGet(urlString);
        HttpResponse response = httpClient.execute(request);
        return response.getEntity().getContent();
    }
}

我已经关注了这个Android培训，我认为它在下载图像而不阻塞主UI方面做得很好。它还处理缓存和滚动许多图像：高效加载大型位图

更新：请注意，这个答案现在非常无效。垃圾回收器对SoftReference和WeakReference进行攻击，因此此代码不适用于新应用。（相反，请尝试其他答案中建议的通用图像加载器之类的库。）

感谢James提供的代码，感谢鲍龙提供的使用SoftReference的建议。我在James的代码上实现了SoftReference更改。不幸的是，SoftReferences导致我的图像被垃圾收集得太快。在我的情况下，没有SoftReference的东西很好，因为我的列表大小有限，图像也很小。

一年前有一场关于谷歌群组上SoftReferences的讨论：链接到线程。作为过早垃圾收集的解决方案，他们建议使用dalvik.system.VMRuntime.setMinimumHeapSize（）手动设置VM堆大小，这对我来说不是很有吸引力。

public DrawableManager() {
    drawableMap = new HashMap<String, SoftReference<Drawable>>();
}

public Drawable fetchDrawable(String urlString) {
    SoftReference<Drawable> drawableRef = drawableMap.get(urlString);
    if (drawableRef != null) {
        Drawable drawable = drawableRef.get();
        if (drawable != null)
            return drawable;
        // Reference has expired so remove the key from drawableMap
        drawableMap.remove(urlString);
    }

    if (Constants.LOGGING) Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
    try {
        InputStream is = fetch(urlString);
        Drawable drawable = Drawable.createFromStream(is, "src");
        drawableRef = new SoftReference<Drawable>(drawable);
        drawableMap.put(urlString, drawableRef);
        if (Constants.LOGGING) Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
                + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
                + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
        return drawableRef.get();
    } catch (MalformedURLException e) {
        if (Constants.LOGGING) Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
        return null;
    } catch (IOException e) {
        if (Constants.LOGGING) Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
        return null;
    }
}

public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {
    SoftReference<Drawable> drawableRef = drawableMap.get(urlString);
    if (drawableRef != null) {
        Drawable drawable = drawableRef.get();
        if (drawable != null) {
            imageView.setImageDrawable(drawableRef.get());
            return;
        }
        // Reference has expired so remove the key from drawableMap
        drawableMap.remove(urlString);
    }

    final Handler handler = new Handler() {
        @Override
        public void handleMessage(Message message) {
            imageView.setImageDrawable((Drawable) message.obj);
        }
    };

    Thread thread = new Thread() {
        @Override
        public void run() {
            //TODO : set imageView to a "pending" image
            Drawable drawable = fetchDrawable(urlString);
            Message message = handler.obtainMessage(1, drawable);
            handler.sendMessage(message);
        }
    };
    thread.start();
}