接收304时，Volley Cache返回null [英] Volley Cache returns null when receiving 304

问题描述

我正在尝试使用其Cache使Volley正常工作.即使设置了"cache-control"，当我收到304时，getCacheEntry().data仍是null.这是我在做什么:

I am trying to get Volley to work using its Cache. When I receive a 304 getCacheEntry().data is null even though "cache-control" is set. Here is what I am doing:

1. Volley像这样被实例化

// Instantiate the cache
Cache cache = new DiskBasedCache(c.getCacheDir(), 10 * 1024 * 1024); // 10 MB cap

// Set up the network to use HttpURLConnection as the HTTP client.
Network network = new BasicNetwork(new HurlStack());

// Instantiate the RequestQueue with the cache and network.
mRequestQueue = new RequestQueue(cache, network);

// Start the queue
mRequestQueue.start();

发送GET请求后，我得到响应200，其中"cache-control"设置为"max-age=180, public".到目前为止一切都好吗?

After sending a GET request I get the response 200 with "cache-control" set to "max-age=180, public". So far so good right?

我做错了什么?由于某种原因，我有一个请求在被触发一次时总是被缓存.甚至可以返回很多数据.但是不会缓存所有其他请求.以下代码段解析响应并检查304.

What am I doing wrong? For some reason I have one request that is always cached when fired once. It's even one that returns a lot of data. But all other requests aren't cached. Following code snippet parses the response and checks for 304.

@Override
protected Response<T> parseNetworkResponse(NetworkResponse response, String charset) { 
    try {
        String json = "";
        if (!response.notModified) {
            json = new String(response.data, charset);
        } else {
            //if not modified -> strangely getCacheEntry().data always null
            json = new String(getCacheEntry().data, charset);
        }
        return Response.success(
                gson.fromJson(json, clazz),
                HttpHeaderParser.parseCacheHeaders(response));

    } catch (UnsupportedEncodingException e) {
        return Response.error(new ParseError(e));
    } catch (JsonSyntaxException e) {
        return Response.error(new ParseError(e));
    }
}

我真的很感谢对此的任何评论.

I really appreciate any comments on this.

推荐答案

恕我直言，由于以下原因，您的缓存条目始终为null(不仅在获取304 resp代码时):

IMHO, your cache entry is always null (not only when getting 304 resp code), because of the following:

Cache cache = new DiskBasedCache(c.getCacheDir(), 10 * 1024 * 1024); // 10 MB cap

请检查您的c.getCacheDir()以查看是否要使用外部存储来存储缓存数据，然后应在AndroidManifest.xml文件中设置WRITE_EXTERNAL_STORAGE权限.

Please check your c.getCacheDir() to see if you want to use External Storage to store cache data, then you should set WRITE_EXTERNAL_STORAGE permission inside AndroidManifest.xml file.

希望这会有所帮助！

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