从 volley 的缓存中加载图像

Question

我使用 volley 在 android 中加载图像和缓存图像。当缓存请求图像时，我想从缓存中加载图像。所以我用下面的方法设置我的图像视图。

public void setImage(String url)
{
    final ImageRequest imgRequest = new ImageRequest(url,
            new Response.Listener<Bitmap>() {
                @Override
                public void onResponse(Bitmap response) {
                    img_thumb.setImageBitmap(response);
                }
            }, 0, 0, ImageView.ScaleType.FIT_XY, Bitmap.Config.ARGB_8888, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            //img_thumb.setBackgroundColor(Color.parseColor("#ff0000"));
            error.printStackTrace();
        }
    });
    MyApplication.getInstance().addToRequestQueue(imgRequest);

}

但是当图像从缓存中可用时，我不知道如何从缓存中加载？

Answer 1

Volley 将在触发图像请求时自动从缓存中提取位图，前提是您使用有效的 ImageCache 对象提供了您创建的 ImageLoader：

    mImageLoader = new ImageLoader(mRequestQueue, new ImageLoader.ImageCache() {

        private final LruCache<String, Bitmap> mMemCache = new LruCache<String, Bitmap>(CACHE_SIZE);

        @Override
        public Bitmap getBitmap(String url) {
            return mMemCache.get(url);
        }

        @Override
        public void putBitmap(String url, Bitmap bitmap) {
            mMemCache.put(url, bitmap);
        }
    });

然后，要加载图像，请使用您创建的 ImageLoader：

/**
 * Performs a request to load an image from a given url.
 * @param url the url to load the image from.
 * @param listener the listener which will receive a call once the image load finishes (either with success or failure). The listener is called on the UI thread.
 * @param maxWidth the max width (in pixels) of the requested image. The returned bitmap will not exceed this width. Use 0 for unlimited
 * @param maxHeight the max height (in pixels) of the requested image. The returned bitmap will not exceed this height. Use 0 for unlimited.
 * @return an ImageContainer object which can be used to access the bitmap once the request has completed, or to cancel the request before it completes.
 */
public ImageLoader.ImageContainer loadImageFromUrl(final String url, final ImageRequestListener listener, int maxWidth, int maxHeight) {


    if (url == null || Uri.parse(url) == null || Uri.parse(url).getHost() == null) {
        Logger.e("VolleyManager: loadImageFromUrl: invalid url " + url);
        listener.onImageLoadFailed();
        return null;
    }

    return mImageLoader.get(url, new ImageLoader.ImageListener() {
        @Override
        public void onResponse(ImageLoader.ImageContainer response, boolean isImmediate) {
            if (listener != null && response.getBitmap() != null) {
                listener.onImageLoadComplete(response.getBitmap());
            } else if (listener != null) {
                listener.onImageLoadFailed(;
            }
        }

        @Override
        public void onErrorResponse(VolleyError error) {
            if (listener != null) {
                listener.onImageLoadFailed();
            }
        }
    }, maxWidth, maxHeight);