android - Volley 缓存不工作

Question

我正在尝试将下载的图像缓存在主视图上，并在详细 View 中显示它们。我测试的方式如下:首先，我在 gridview 上显示所有图像并断开 Internet 并希望在细节上查看缓存图像。但是，在详细信息 Activity 中未显示图像。

我正在使用以下 Volley Singleton 类，如下所示:

public class CustomVolleyRequest {

    private static CustomVolleyRequest customVolleyRequest;
    private static Context context;
    private RequestQueue requestQueue;
    private ImageLoader imageLoader;

    private CustomVolleyRequest(Context context) {
        CustomVolleyRequest.context = context;
        this.requestQueue = getRequestQueue();

        imageLoader = new ImageLoader(requestQueue,
                new ImageLoader.ImageCache() {
                    private final LruCache<String, Bitmap>
                            cache = new LruCache<>(20);

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

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

    public static synchronized CustomVolleyRequest getInstance(Context context) {
        if (customVolleyRequest == null) {
            customVolleyRequest = new CustomVolleyRequest(context);
        }
        return customVolleyRequest;
    }

    public RequestQueue getRequestQueue() {
        if (requestQueue == null) {
            requestQueue = Volley.newRequestQueue(context.getApplicationContext(), 10 * 1024 * 1024);
        }
        return requestQueue;
    }

    ImageLoader getImageLoader() {
        return imageLoader;
    }
}

主要 Activity 适配器

public View getView(final int position, View convertView, @NonNull ViewGroup parent) {
    final ViewHolder holder;
    if(convertView == null) {
        holder = new ViewHolder();
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.grid_item, parent, false);
    }
  holder.imageView.setImageUrl(imageURL, mImageLoader);
}

详细 Activity

// I have checked and confirmed that the following url is same with the one the main activity
String url = getArguments().getString("image_url");
ImageLoader imageLoader = CustomVolleyRequest.getInstance(getContext()).getImageLoader();
mImageView.setImageUrl(url, imageLoader);

Answer 1

我认为 Volley 缓存仍然有效，但是，这里的问题是因为详细 Activity 中的 NetworkImageView 与主要 Activity 中的 NetworkImageView 不同，它还需要先成功加载一次图像。在这里，您在开始详细 Activity 之前断开 Internet。

可以看到NetworkImageView.java里面的逻辑

注意#122 中的几行

// if there was an old request in this view, check if it needs to be canceled.
        if (mImageContainer != null && mImageContainer.getRequestUrl() != null) {...

和#134

// The pre-existing content of this view didn't match the current URL. Load the new image
        // from the network.
        ImageContainer newContainer = mImageLoader.get(mUrl,...

---

更新 2017/02/10

当 NetworkImageView inside detail Activity 从网络加载新图像时 (ImageContainer newContainer = mImageLoader.get...)，方法 get里面ImageLoader.java将被调用。

查看代码:

...
final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight);
// Try to look up the request in the cache of remote images.
Bitmap cachedBitmap = mCache.getBitmap(cacheKey);
if (cachedBitmap != null) {
    // Return the cached bitmap.
    ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, null, null);
    imageListener.onResponse(container, true);
    return container;
}
...

你会发现，如果两个 Activity 中的 ImageView 具有相同的宽度和高度，那么 cacheKey 也会相同，并且 cachedBitmap 将不为空，缓存的位图也将用于 NetworkImageView inside detail Activity 。