Android：Volley不能在離線狀態下使用緩存

Question

我已經添加了針對獲取Json對象的請求，如果wifi已打開，則需要數據，但在離線模式下無法訪問，即使緩存啓用了請求。

我做下面的代碼

public class VolleySingleton extends Application 
{ 
    public static final String TAG = VolleySingleton.class.getSimpleName(); 
    private RequestQueue mRequestQueue; 
    private static VolleySingleton mInstance; 
    private ImageLoader mImageLoader; 
    private final String DEFAULT_CACHE_DIR = "sl_cache"; 

    @Override 
    public void onConfigurationChanged(Configuration newConfig) 
    { 
     super.onConfigurationChanged(newConfig); 
    } 

    @Override 
    public void onCreate() 
    { 
     super.onCreate(); 
     mInstance = this; 
    } 

    public static synchronized VolleySingleton getInstance() 
    { 
     return mInstance; 
    } 

    public ImageLoader getImageLoader() 
    { 
     getRequestQueue(); 
     if (mImageLoader == null) 
     { 
      mImageLoader = new ImageLoader(this.mRequestQueue, new LruBitmapCache()); 
     } 
     return this.mImageLoader; 
    } 

    public <T> void addToRequestQueue(Request<T> req, String tag) 
    { 
     // set the default tag if tag is empty 
     req.setTag(TextUtils.isEmpty(tag) ? TAG : tag); 
     getRequestQueue().add(req); 
    } 

    public <T> void addToRequestQueue(Request<T> req) 
    { 
     req.setTag(TAG); 
     getRequestQueue().add(req); 
    } 

    public void cancelPendingRequests(Object tag) 
    { 
     if (mRequestQueue != null) 
     { 
      mRequestQueue.cancelAll(tag); 
     } 
    } 

    public RequestQueue getRequestQueue() 
    { 
     if (mRequestQueue == null) 
     { 
      Cache cache = new DiskBasedCache(getCacheDir(), 1024 * 1024 * 10); // 10MB cap 
      Network network = new BasicNetwork(new HurlStack()); 
      mRequestQueue = new RequestQueue(cache, network); 
      mRequestQueue.start(); 
     } 
     return mRequestQueue; 
    } 
} 


private void getData(String url, String tag) 
{ 
      final JsonObjectRequest jsonObjReq = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() 
      { 
       @Override 
       public void onResponse(JSONObject response) 
       { 
        Log.wtf("HOME", response.toString()); 
        String result = parseData(response.toString()); 
        postProcessing(result); 
        //SocialLadder.getInstance().getRequestQueue().getCache().invalidate(url, true); 
       } 


      }, new Response.ErrorListener() 
      { 
       @Override 
       public void onErrorResponse(VolleyError error) 
       { 
        VolleyLog.wtf("HOME", "Error: " + error.getMessage()); 
        stopRefresher(); 
       } 
      }) 
      { 
       @Override 
       protected Response<JSONObject> parseNetworkResponse(NetworkResponse response) 
       {       
        try 
        { 
         String jsonString = new String(response.data, HttpHeaderParser.parseCharset(response.headers)); 
         return !jsonString.isEmpty() ? Response.success(new JSONObject(jsonString), HttpHeaderParser.parseCacheHeaders(response)) : Response.success(new JSONObject(), HttpHeaderParser.parseCacheHeaders(response)); 
        } 
        catch (JSONException ex) 
        { 
         ex.printStackTrace(); 
        } 
        catch (UnsupportedEncodingException e) 
        { 
         e.printStackTrace(); 
        } 
        return null; 
       } 
      }; 
      jsonObjReq.setShouldCache(true); 
      VolleySingleton.getInstance().addToRequestQueue(jsonObjReq, tag); 
} 

請幫幫忙，我想我的緩存畫面數據。

編輯

緩存數據

private String getCache(String url) 
    { 
     String data = ""; 
     Cache cache = VolleySingleton.getInstance().getRequestQueue().getCache(); 
     Cache.Entry entry = cache.get(url); 
     if (entry != null) 
     { 
      try 
      { 
       data = new String(entry.data, "UTF-8"); 
       // handle data, like converting it to xml, json, bitmap etc., 
      } 
      catch (UnsupportedEncodingException e) 
      { 
       e.printStackTrace(); 
      } 
     } 
     /*else 
     { 
      // Cached response doesn't exists. Make network call here 
     }*/ 
     return data; 
    } 

Answer 1

爲了與你需要有兩件事情Volley緩存內容：

1）服務器，可以緩存它。它通常出現在cache control tag的HTTP header中。

2）你保存它或在這種情況下，你告訴Volly保存。

所以我認爲你的問題是在第一。這意味着服務器劑量不允許緩存這些文件，以確認我的答案，你可以做這些事情之一：

1. 下載該插件（RESTClient實現）爲mozilla和發送您的請求，並檢查頭文件進行緩存控制。如果服務器劑量不會允許你緩存你會看到類似下面的圖片，notice cache control tag

設定破壞在headerValue = headers.get("Cache-Control");點HttpHeaderParse類，看看怎麼回事當Volley想解析cache control tag。

Answer 2

就在** BasicNetwork *類中添加這一行或修改如下

@Override 
    public NetworkResponse performRequest(Request<?> request) throws VolleyError { 
    long requestStart = SystemClock.elapsedRealtime(); 
    while (true) { 

     HttpResponse httpResponse = null; 
     byte[] responseContents = null; 
     Map<String, String> responseHeaders = Collections.emptyMap(); 
     try { 
     if(!ConnectivityUtils.isNetworkEnabled(BBApplication.getContext())) { 
       return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, 
         request.getCacheEntry().data, responseHeaders, true); 
      } 

      // Gather headers. 
      Map<String, String> headers = new HashMap<String, String>(); 
      addCacheHeaders(headers, request.getCacheEntry()); 
      httpResponse = mHttpStack.performRequest(request, headers); 
      StatusLine statusLine = httpResponse.getStatusLine(); 
      int statusCode = statusLine.getStatusCode(); 
      responseHeaders = convertHeaders(httpResponse.getAllHeaders()); 
      // Handle cache validation. 


      if (statusCode == HttpStatus.SC_NOT_MODIFIED) { 
       Cache.Entry entry = request.getCacheEntry(); 

       if (entry == null) { 
        return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, null, responseHeaders, true, SystemClock.elapsedRealtime() - requestStart); 
       } 

       // A HTTP 304 response does not have all header fields. We 
       // have to use the header fields from the cache entry plus 
       // the new ones from the response. 
       // http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5 
       entry.responseHeaders.putAll(responseHeaders); 
       return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, entry.data, entry.responseHeaders, true, SystemClock.elapsedRealtime() - requestStart); 
      } 
      // Some responses such as 204s do not have content. We must check. 
      if (httpResponse.getEntity() != null) { 
       responseContents = entityToBytes(httpResponse.getEntity()); 
      } else { 
       // Add 0 byte response as a way of honestly representing a 
       // no-content request. 
       responseContents = new byte[0]; 
      } 

      // if the request is slow, log it. 
      long requestLifetime = SystemClock.elapsedRealtime() - requestStart; 
      logSlowRequests(requestLifetime, request, responseContents, statusLine); 

      if (statusCode < 200 || statusCode > 299) { 
       throw new IOException(); 
      } 
      return new NetworkResponse(statusCode, responseContents, responseHeaders, false, SystemClock.elapsedRealtime() - requestStart); 
     } catch (SocketTimeoutException e) { 
      attemptRetryOnException("socket", request, new TimeoutError()); 
     } catch (ConnectTimeoutException e) { 
      attemptRetryOnException("connection", request, new TimeoutError()); 
     } catch (NoHttpResponseException e) { 
      attemptRetryOnException("socket", request, new TimeoutError()); 
     } catch (UnknownHostException e) { 
      attemptRetryOnException("socket", request, new TimeoutError()); 
     } catch (MalformedURLException e) { 
      throw new RuntimeException("Bad URL " + request.getUrl(), e); 
     } catch (IOException e) { 
      int statusCode = 0; 
      NetworkResponse networkResponse = null; 
      if (httpResponse != null) { 
       statusCode = httpResponse.getStatusLine().getStatusCode(); 
      } else { 
       throw new NoConnectionError(e); 
      } 
      VolleyLog.e("Unexpected response code %d for %s", statusCode, request.getUrl()); 
      if (responseContents != null) { 
       networkResponse = new NetworkResponse(statusCode, responseContents, responseHeaders, false, SystemClock.elapsedRealtime() - requestStart); 
       if (statusCode == HttpStatus.SC_UNAUTHORIZED || statusCode == HttpStatus.SC_FORBIDDEN) { 
        attemptRetryOnException("auth", request, new AuthFailureError(networkResponse)); 
       } else { 
        // TODO: Only throw ServerError for 5xx status codes. 
        throw new ServerError(networkResponse); 
       } 
      } else { 
       throw new NetworkError(networkResponse); 
      } 
     } 
    } 
} 

和數據請求到期，您可以使用使用改變Cached.Entry自己HttpHeaderParser

點擊代碼BasicNetwork

這段代碼是做什麼的，它將檢查互聯網連接和網絡調用，如果它有緩存副本則恢復。

注意API響應應該是可緩存的，因爲如果響應頭允許，Volley只緩存數據。 See here for Cached Control Header