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

我使用droidQuery。从URL加载图像有两种机制。第一个（速记）简单地是：

$.with(myView).image(url);

这可以很容易地添加到ArrayAdapter的getView（…）方法中。

longhand方法将提供更多的控制，并具有此处未讨论的选项（如缓存和回调），但可以在此处找到将输出大小指定为200px x 200px的基本实现：

$.ajax(new AjaxOptions().url(url)
    .type("GET")
    .dataType("image")
    .imageWidth(200).imageHeight(200)
    .success(new Function() {
        @Override
        public void invoke($ droidQuery, Object... params) {
            myImageView.setImageBitmap((Bitmap) params[0]);
        }
    })
    .error(new Function() {
        @Override
        public void invoke($ droidQuery, Object... params) {
            AjaxError e = (AjaxError) params[0];
            Log.e("$", "Error " + e.status + ": " + e.error);
        }
    })
);

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();
}

这就是使用Jetpack Compose的方法。

implementation("io.coil-kt:coil-compose:1.3.1") // Add the Coil-Compose library

Image(
    painter = rememberImagePainter("https://www.example.com/image.jpg"),
    contentDescription = "My image description",
    modifier = Modifier.size(128.dp)
)

感谢nglauber和Gabriele Mariotti的回答。

我遇到了这个问题，并实现了lruCache。我相信你需要API 12或更高版本，或者使用兼容的v4库。lurCache是快速内存，但它也有预算，所以如果你担心，你可以使用磁盘缓存。。。这都在缓存位图中描述。

现在我将提供我的实现，它是我从任何地方调用的单例，如下所示：

//Where the first is a string and the other is a imageview to load.

DownloadImageTask.getInstance().loadBitmap(avatarURL, iv_avatar);

以下是理想的代码，在检索web图像时，缓存并在适配器的getView中调用上述代码：

public class DownloadImageTask {

    private LruCache<String, Bitmap> mMemoryCache;

    /* Create a singleton class to call this from multiple classes */

    private static DownloadImageTask instance = null;

    public static DownloadImageTask getInstance() {
        if (instance == null) {
            instance = new DownloadImageTask();
        }
        return instance;
    }

    //Lock the constructor from public instances
    private DownloadImageTask() {

        // Get max available VM memory, exceeding this amount will throw an
        // OutOfMemory exception. Stored in kilobytes as LruCache takes an
        // int in its constructor.
        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);

        // Use 1/8th of the available memory for this memory cache.
        final int cacheSize = maxMemory / 8;

        mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap bitmap) {
                // The cache size will be measured in kilobytes rather than
                // number of items.
                return bitmap.getByteCount() / 1024;
            }
        };
    }

    public void loadBitmap(String avatarURL, ImageView imageView) {
        final String imageKey = String.valueOf(avatarURL);

        final Bitmap bitmap = getBitmapFromMemCache(imageKey);
        if (bitmap != null) {
            imageView.setImageBitmap(bitmap);
        } else {
            imageView.setImageResource(R.drawable.ic_launcher);

            new DownloadImageTaskViaWeb(imageView).execute(avatarURL);
        }
    }

    private void addBitmapToMemoryCache(String key, Bitmap bitmap) {
        if (getBitmapFromMemCache(key) == null) {
            mMemoryCache.put(key, bitmap);
        }
    }

    private Bitmap getBitmapFromMemCache(String key) {
        return mMemoryCache.get(key);
    }

    /* A background process that opens a http stream and decodes a web image. */

    class DownloadImageTaskViaWeb extends AsyncTask<String, Void, Bitmap> {
        ImageView bmImage;

        public DownloadImageTaskViaWeb(ImageView bmImage) {
            this.bmImage = bmImage;
        }

        protected Bitmap doInBackground(String... urls) {

            String urldisplay = urls[0];
            Bitmap mIcon = null;
            try {
                InputStream in = new java.net.URL(urldisplay).openStream();
                mIcon = BitmapFactory.decodeStream(in);

            } 
            catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }

            addBitmapToMemoryCache(String.valueOf(urldisplay), mIcon);

            return mIcon;
        }

        /* After decoding we update the view on the main UI. */
        protected void onPostExecute(Bitmap result) {
            bmImage.setImageBitmap(result);
        }
    }
}

看看Shutterbug，Applidium的轻量级SDWebImage（iOS上的一个不错的库）到Android的端口。它支持异步缓存，存储失败的URL，很好地处理并发，并包含有用的子类。

也欢迎拉取请求（和错误报告）！