Retrofit 與 OKHttp 可以在離線時利用快取資料嗎?
在嘗試使用 Retrofit 和 OKHttp 快取 HTTP 回應時,您遇到了以下問題離線時取得 RetrofitError UnknownHostException。這表明 Retrofit 無法檢索快取的資料。要解決此問題,需要進行以下修改:
針對Retrofit 2.x 進行編輯:
實作OkHttp 攔截器來管理快取邏輯:
<code class="java">private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() { @Override public Response intercept(Chain chain) throws IOException { Response originalResponse = chain.proceed(chain.request()); if (Utils.isNetworkAvailable(context)) { int maxAge = 60; // read from cache for 1 minute return originalResponse.newBuilder() .header("Cache-Control", "public, max-age=" + maxAge) .build(); } else { int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale return originalResponse.newBuilder() .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale) .build(); } } }</code>
為OkHttpClient 設定攔截器與快取:
<code class="java">OkHttpClient client = new OkHttpClient(); client.networkInterceptors().add(REWRITE_CACHE_CONTROL_INTERCEPTOR); //setup cache File httpCacheDirectory = new File(context.getCacheDir(), "responses"); int cacheSize = 10 * 1024 * 1024; // 10 MiB Cache cache = new Cache(httpCacheDirectory, cacheSize); //add cache to the client client.setCache(cache);</code>
將OkHttpClient >
<code class="java">Retrofit retrofit = new Retrofit.Builder() .baseUrl(BASE_URL) .client(client) .addConverterFactory(GsonConverterFactory.create()) .build();</code>
<code class="java"> File httpCacheDirectory = new File(context.getCacheDir(), "responses"); Cache cache = null; try { cache = new Cache(httpCacheDirectory, 10 * 1024 * 1024); } catch (IOException e) { Log.e("OKHttp", "Could not create http cache", e); } OkHttpClient okHttpClient = new OkHttpClient(); if (cache != null) { okHttpClient.setCache(cache); } ...</code>
原始答案:
<code class="java">RestAdapter.Builder builder= new RestAdapter.Builder() .setRequestInterceptor(new RequestInterceptor() { @Override public void intercept(RequestFacade request) { request.addHeader("Accept", "application/json;versions=1"); if (MyApplicationUtils.isNetworkAvailable(context)) { int maxAge = 60; // read from cache for 1 minute request.addHeader("Cache-Control", "public, max-age=" + maxAge); } else { int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale request.addHeader("Cache-Control", "public, only-if-cached, max-stale=" + maxStale); } } });</code>
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