public class ImageDownloader {

Map<String, Bitmap> imageCache;

public ImageDownloader() {
    imageCache = new HashMap<String, Bitmap>();

}

// download function
public void download(String url, ImageView imageView) {
    if (cancelPotentialDownload(url, imageView)) {

        // Caching code right here
        String filename = String.valueOf(url.hashCode());
        File f = new File(getCacheDirectory(imageView.getContext()),
                filename);

        // Is the bitmap in our memory cache?
        Bitmap bitmap = null;

        bitmap = (Bitmap) imageCache.get(f.getPath());

        if (bitmap == null) {

            bitmap = BitmapFactory.decodeFile(f.getPath());

            if (bitmap != null) {
                imageCache.put(f.getPath(), bitmap);
            }

        }
        // No? download it
        if (bitmap == null) {
            try {
                BitmapDownloaderTask task = new BitmapDownloaderTask(
                        imageView);
                DownloadedDrawable downloadedDrawable = new DownloadedDrawable(
                        task);
                imageView.setImageDrawable(downloadedDrawable);
                task.execute(url);
            } catch (Exception e) {
                Log.e("Error==>", e.toString());
            }

        } else {
            // Yes? set the image
            imageView.setImageBitmap(bitmap);
        }
    }
}

// cancel a download (internal only)
private static boolean cancelPotentialDownload(String url,
        ImageView imageView) {
    BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);

    if (bitmapDownloaderTask != null) {
        String bitmapUrl = bitmapDownloaderTask.url;
        if ((bitmapUrl == null) || (!bitmapUrl.equals(url))) {
            bitmapDownloaderTask.cancel(true);
        } else {
            // The same URL is already being downloaded.
            return false;
        }
    }
    return true;
}

// gets an existing download if one exists for the imageview
private static BitmapDownloaderTask getBitmapDownloaderTask(
        ImageView imageView) {
    if (imageView != null) {
        Drawable drawable = imageView.getDrawable();
        if (drawable instanceof DownloadedDrawable) {
            DownloadedDrawable downloadedDrawable = (DownloadedDrawable) drawable;
            return downloadedDrawable.getBitmapDownloaderTask();
        }
    }
    return null;
}

// our caching functions
// Find the dir to save cached images
private static File getCacheDirectory(Context context) {
    String sdState = android.os.Environment.getExternalStorageState();
    File cacheDir;

    if (sdState.equals(android.os.Environment.MEDIA_MOUNTED)) {
        File sdDir = android.os.Environment.getExternalStorageDirectory();

        // TODO : Change your diretcory here
        cacheDir = new File(sdDir, "data/ToDo/images");
    } else
        cacheDir = context.getCacheDir();

    if (!cacheDir.exists())
        cacheDir.mkdirs();
    return cacheDir;
}

private void writeFile(Bitmap bmp, File f) {
    FileOutputStream out = null;

    try {
        out = new FileOutputStream(f);
        bmp.compress(Bitmap.CompressFormat.PNG, 80, out);
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            if (out != null)
                out.close();
        } catch (Exception ex) {
        }
    }
}

// download asynctask
public class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
    private String url;
    private final WeakReference<ImageView> imageViewReference;

    public BitmapDownloaderTask(ImageView imageView) {
        imageViewReference = new WeakReference<ImageView>(imageView);
    }

    @Override
    // Actual download method, run in the task thread
    protected Bitmap doInBackground(String... params) {
        // params comes from the execute() call: params[0] is the url.
        url = (String) params[0];
        return downloadBitmap(params[0]);
    }

    @Override
    // Once the image is downloaded, associates it to the imageView
    protected void onPostExecute(Bitmap bitmap) {
        if (isCancelled()) {
            bitmap = null;
        }

        if (imageViewReference != null) {
            ImageView imageView = imageViewReference.get();
            BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
            // Change bitmap only if this process is still associated with
            // it
            if (this == bitmapDownloaderTask) {
                imageView.setImageBitmap(bitmap);

                // cache the image

                String filename = String.valueOf(url.hashCode());
                File f = new File(
                        getCacheDirectory(imageView.getContext()), filename);

                imageCache.put(f.getPath(), bitmap);

                writeFile(bitmap, f);
            }
        }
    }

}

static class DownloadedDrawable extends ColorDrawable {
    private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference;

    public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) {
        super(Color.WHITE);
        bitmapDownloaderTaskReference = new WeakReference<BitmapDownloaderTask>(
                bitmapDownloaderTask);
    }

    public BitmapDownloaderTask getBitmapDownloaderTask() {
        return bitmapDownloaderTaskReference.get();
    }
}

// the actual download code
static Bitmap downloadBitmap(String url) {
    HttpParams params = new BasicHttpParams();
    params.setParameter(CoreProtocolPNames.PROTOCOL_VERSION,
            HttpVersion.HTTP_1_1);
    HttpClient client = new DefaultHttpClient(params);
    final HttpGet getRequest = new HttpGet(url);

    try {
        HttpResponse response = client.execute(getRequest);
        final int statusCode = response.getStatusLine().getStatusCode();
        if (statusCode != HttpStatus.SC_OK) {
            Log.w("ImageDownloader", "Error " + statusCode
                    + " while retrieving bitmap from " + url);
            return null;
        }

        final HttpEntity entity = response.getEntity();
        if (entity != null) {
            InputStream inputStream = null;
            try {
                inputStream = entity.getContent();
                final Bitmap bitmap = BitmapFactory
                        .decodeStream(inputStream);
                return bitmap;
            } finally {
                if (inputStream != null) {
                    inputStream.close();
                }
                entity.consumeContent();
            }
        }
    } catch (Exception e) {
        // Could provide a more explicit error message for IOException or
        // IllegalStateException
        getRequest.abort();
        Log.w("ImageDownloader", "Error while retrieving bitmap from "
                + url + e.toString());
    } finally {
        if (client != null) {
            // client.close();
        }
    }
    return null;
 }
}

对于那些对使用什么库来延迟加载图像犹豫不决的人来说，这只是一个快速提示：

有四种基本方法。

DIY=>不是最好的解决方案，但对于一些图像，如果你想不使用其他库的麻烦Volley的懒加载库=>来自android的家伙。它很好，一切都很好，但文档记录很差，因此使用起来有问题。毕加索：一个简单可行的解决方案，你甚至可以指定你想要引入的图像大小。它非常简单，但对于需要处理大量图像的应用程序来说，可能不是很“高效”。UIL：延迟加载图像的最佳方式。您可以缓存图像（当然需要权限），初始化加载程序一次，然后完成工作。迄今为止，我见过最成熟的异步图像加载库。

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。

1.Picasso允许在应用程序中轻松加载图像，通常只需一行代码！

使用渐变：

implementation 'com.squareup.picasso:picasso:(insert latest version)'

只有一行代码！

Picasso.get().load("http://i.imgur.com/DvpvklR.png").into(imageView);

2.Glide Android的图像加载和缓存库，专注于平滑滚动

使用渐变：

repositories {
  mavenCentral() 
  google()
}

dependencies {
   implementation 'com.github.bumptech.glide:glide:4.11.0'
   annotationProcessor 'com.github.bumptech.glide:compiler:4.11.0'
}

//对于简单视图：

  Glide.with(this).load("http://i.imgur.com/DvpvklR.png").into(imageView);

3.湿壁画是一个在Android中显示图像的强大系统Fresco负责图像加载和显示到

壁画入门

你必须试试这个通用加载器。我在做了很多关于延迟加载的RnD之后使用了这个。

通用图像加载器

特征

多线程图像加载（异步或同步）ImageLoader配置的广泛定制（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）每个显示图像调用都有许多自定义选项（存根图像、缓存开关、解码选项、位图处理和显示等）内存和/或磁盘上的图像缓存（设备的文件系统或SD卡）收听加载过程（包括下载进度）

Android 2.0+支持

使用滑动库。它适用于我，也适用于你的代码。它也适用于图像和gif。

ImageView imageView = (ImageView) findViewById(R.id.test_image); 
    GlideDrawableImageViewTarget imagePreview = new GlideDrawableImageViewTarget(imageView);
    Glide
            .with(this)
            .load(url)
            .listener(new RequestListener<String, GlideDrawable>() {
                @Override
                public boolean onException(Exception e, String model, Target<GlideDrawable> target, boolean isFirstResource) {                       
                    return false;
                }

                @Override
                public boolean onResourceReady(GlideDrawable resource, String model, Target<GlideDrawable> target, boolean isFromMemoryCache, boolean isFirstResource) {
                    return false;
                }
            })
            .into(imagePreview);
}