[转载]Asynchronous HTTP Requests in Android Using Volley – 张兴业 – 博客园.
Volley是Android开发者新的瑞士军刀,它提供了优美的框架,使得Android应用程序网络访问更容易和更快。Volley抽象实现了底层的 HTTP Client库,让你不关注HTTP Client细节,专注于写出更加漂亮、干净的RESTful HTTP请求。另外,Volley请求会异步执行,不阻挡主线程。
Volley提供的功能
简单的讲,提供了如下主要的功能:
1、封装了的异步的RESTful 请求API;
2、一个优雅和稳健的请求队列;
3、一个可扩展的架构,它使开发人员能够实现自定义的请求和响应处理机制;
4、能够使用外部HTTP Client库;
5、缓存策略;
6、自定义的网络图像加载视图(NetworkImageView,ImageLoader等);
为什么使用异步HTTP请求?
Android中要求HTTP请求异步执行,如果在主线程执行HTTP请求,可能会抛出android.os.NetworkOnMainThreadException 异常。阻塞主线程有一些严重的后果,它阻碍UI渲染,用户体验不流畅,它可能会导致可怕的ANR(Application Not Responding)。要避免这些陷阱,作为一个开发者,应该始终确保HTTP请求是在一个不同的线程。
怎样使用Volley
这篇博客将会详细的介绍在应用程程中怎么使用volley,它将包括一下几方面:
1、安装和使用Volley库
2、使用请求队列
3、异步的JSON、String请求
4、取消请求
5、重试失败的请求,自定义请求超时
6、设置请求头(HTTP headers)
7、使用Cookies
8、错误处理
安装和使用Volley库
引入Volley非常简单,首先,从git库先克隆一个下来:
git clone https://android.googlesource.com/platform/frameworks/volley
然后编译为jar包,再把jar包放到自己的工程的libs目录。
使用请求队列
Volley的所有请求都放在一个队列,然后进行处理,这里是你如何将创建一个请求队列:
RequestQueue mRequestQueue = Volley.newRequestQueue(this); // 'this' is Context
理想的情况是把请求队列集中放到一个地方,最好是初始化应用程序类中初始化请求队列,下面类做到了这一点:
<span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > class </span><span class = "pln" > </span><span class = "typ" >ApplicationController</span><span class = "pln" > </span><span class = "kwd" > extends </span><span class = "pln" > </span><span class = "typ" >Application</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > /** * Log or request TAG */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "kwd" > final </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > TAG </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "str" > "VolleyPatterns" </span><span class = "pun" >;</span><span class = "pln" > </span><span class = "com" > /** * Global request queue for Volley */ </span><span class = "pln" > </span><span class = "kwd" > private </span><span class = "pln" > </span><span class = "typ" >RequestQueue</span><span class = "pln" > mRequestQueue</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "com" > /** * A singleton instance of the application class for easy access in other places */ </span><span class = "pln" > </span><span class = "kwd" > private </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "typ" >ApplicationController</span><span class = "pln" > sInstance</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onCreate</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > super </span><span class = "pun" >.</span><span class = "pln" >onCreate</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "com" > // initialize the singleton</span><span class="pln"> sInstance </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > this </span><span class = "pun" >;</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * @return ApplicationController singleton instance */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "kwd" > synchronized </span><span class = "pln" > </span><span class = "typ" >ApplicationController</span><span class = "pln" > getInstance</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > sInstance</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * @return The Volley Request queue, the queue will be created if it is null */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "typ" >RequestQueue</span><span class = "pln" > getRequestQueue</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // lazy initialize the request queue, the queue instance will be</span><span class="pln"> </span><span class = "com" > // created when it is accessed for the first time</span><span class="pln"> </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >mRequestQueue </span><span class = "pun" >==</span><span class = "pln" > </span><span class = "kwd" > null </span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > mRequestQueue </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "typ" >Volley</span><span class = "pun" >.</span><span class = "pln" >newRequestQueue</span><span class = "pun" >(</span><span class = "pln" >getApplicationContext</span><span class = "pun" >());</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > mRequestQueue</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Adds the specified request to the global queue, if tag is specified * then it is used else Default TAG is used. * * @param req * @param tag */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > addToRequestQueue</span><span class = "pun" >(</span><span class = "typ" >Request</span><span class = "pln" > req</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > tag</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // set the default tag if tag is empty</span><span class="pln"> req</span><span class = "pun" >.</span><span class = "pln" >setTag</span><span class = "pun" >(</span><span class = "typ" >TextUtils</span><span class = "pun" >.</span><span class = "pln" >isEmpty</span><span class = "pun" >(</span><span class = "pln" >tag</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >?</span><span class = "pln" > TAG </span><span class = "pun" >:</span><span class = "pln" > tag</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >d</span><span class = "pun" >(</span><span class = "str" > "Adding request to queue: %s" </span><span class = "pun" >,</span><span class = "pln" > req</span><span class = "pun" >.</span><span class = "pln" >getUrl</span><span class = "pun" >());</span><span class = "pln" > getRequestQueue</span><span class = "pun" >().</span><span class = "pln" >add</span><span class = "pun" >(</span><span class = "pln" >req</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Adds the specified request to the global queue using the Default TAG. * * @param req * @param tag */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > addToRequestQueue</span><span class = "pun" >(</span><span class = "typ" >Request</span><span class = "pln" > req</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // set the default tag if tag is empty</span><span class="pln"> req</span><span class = "pun" >.</span><span class = "pln" >setTag</span><span class = "pun" >(</span><span class = "pln" >TAG</span><span class = "pun" >);</span><span class = "pln" > getRequestQueue</span><span class = "pun" >().</span><span class = "pln" >add</span><span class = "pun" >(</span><span class = "pln" >req</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Cancels all pending requests by the specified TAG, it is important * to specify a TAG so that the pending/ongoing requests can be cancelled. * * @param tag */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > cancelPendingRequests</span><span class = "pun" >(</span><span class = "typ" >Object</span><span class = "pln" > tag</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >mRequestQueue </span><span class = "pun" >!=</span><span class = "pln" > </span><span class = "kwd" > null </span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > mRequestQueue</span><span class = "pun" >.</span><span class = "pln" >cancelAll</span><span class = "pun" >(</span><span class = "pln" >tag</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span> |
异步的JSON、String请求
Volley提供了以下的实用工具类进行异步HTTP请求:
- JsonObjectRequest — To send and receive JSON Object from the Server
- JsonArrayRequest — To receive JSON Array from the Server
- StringRequest — To retrieve response body as String (ideally if you intend to parse the response by yourself)
JsonObjectRequest
这个类可以用来发送和接收JSON对象。这个类的一个重载构造函数允许设置适当的请求方法(DELETE,GET,POST和PUT)。如果您正在使用一个RESTful服务端,可以使用这个类。下面的示例显示如何使GET和POST请求。
GET请求:
<span class = "kwd" > final </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > URL </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "str" > "/volley/resource/12" </span><span class = "pun" >;</span><span class = "pln" > </span><span class = "com" > // pass second argument as "null" for GET requests</span><span class="pln"> </span><span class = "typ" >JsonObjectRequest</span><span class = "pln" > req </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >JsonObjectRequest</span><span class = "pun" >(</span><span class = "pln" >URL</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > null </span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >Listener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onResponse</span><span class = "pun" >(</span><span class = "typ" >JSONObject</span><span class = "pln" > response</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > try </span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >v</span><span class = "pun" >(</span><span class = "str" > "Response:%n %s" </span><span class = "pun" >,</span><span class = "pln" > response</span><span class = "pun" >.</span><span class = "pln" >toString</span><span class = "pun" >(</span><span class = "lit" > 4 </span><span class = "pun" >));</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > catch </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "typ" >JSONException</span><span class = "pln" > e</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > e</span><span class = "pun" >.</span><span class = "pln" >printStackTrace</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >},</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >ErrorListener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onErrorResponse</span><span class = "pun" >(</span><span class = "typ" >VolleyError</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >e</span><span class = "pun" >(</span><span class = "str" > "Error: " </span><span class = "pun" >,</span><span class = "pln" > error</span><span class = "pun" >.</span><span class = "pln" >getMessage</span><span class = "pun" >());</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >});</span><span class = "pln" > </span><span class = "com" > // add the request object to the queue to be executed</span><span class="pln"> </span><span class = "typ" >ApplicationController</span><span class = "pun" >.</span><span class = "pln" >getInstance</span><span class = "pun" >().</span><span class = "pln" >addToRequestQueue</span><span class = "pun" >(</span><span class = "pln" >req</span><span class = "pun" >);</span><span class = "pln" > </span> |
POST请求:
<span class = "kwd" > final </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > URL </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "str" > "/volley/resource/12" </span><span class = "pun" >;</span><span class = "pln" > </span><span class = "com" > // Post params to be sent to the server</span><span class="pln"> </span><span class = "typ" >HashMap</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "kwd" >params</span><span class = "pln" > </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >HashMap</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;();</span><span class = "pln" > </span><span class = "kwd" >params</span><span class = "pun" >.</span><span class = "pln" >put</span><span class = "pun" >(</span><span class = "str" > "token" </span><span class = "pun" >,</span><span class = "pln" > </span><span class = "str" > "AbCdEfGh123456" </span><span class = "pun" >);</span><span class = "pln" > </span><span class = "typ" >JsonObjectRequest</span><span class = "pln" > req </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >JsonObjectRequest</span><span class = "pun" >(</span><span class = "pln" >URL</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >JSONObject</span><span class = "pun" >(</span><span class = "kwd" >params</span><span class = "pun" >),</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >Listener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onResponse</span><span class = "pun" >(</span><span class = "typ" >JSONObject</span><span class = "pln" > response</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > try </span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >v</span><span class = "pun" >(</span><span class = "str" > "Response:%n %s" </span><span class = "pun" >,</span><span class = "pln" > response</span><span class = "pun" >.</span><span class = "pln" >toString</span><span class = "pun" >(</span><span class = "lit" > 4 </span><span class = "pun" >));</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > catch </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "typ" >JSONException</span><span class = "pln" > e</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > e</span><span class = "pun" >.</span><span class = "pln" >printStackTrace</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >},</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >ErrorListener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onErrorResponse</span><span class = "pun" >(</span><span class = "typ" >VolleyError</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >e</span><span class = "pun" >(</span><span class = "str" > "Error: " </span><span class = "pun" >,</span><span class = "pln" > error</span><span class = "pun" >.</span><span class = "pln" >getMessage</span><span class = "pun" >());</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >});</span><span class = "pln" > </span><span class = "com" > // add the request object to the queue to be executed</span><span class="pln"> </span><span class = "typ" >ApplicationController</span><span class = "pun" >.</span><span class = "pln" >getInstance</span><span class = "pun" >().</span><span class = "pln" >addToRequestQueue</span><span class = "pun" >(</span><span class = "pln" >req</span><span class = "pun" >);</span> |
JsonArrayRequest
这个类可以用来接受 JSON Arrary,不支持JSON Object。这个类现在只支持 HTTP GET。由于支持GET,你可以在URL的后面加上请求参数。类的构造函数不支持请求参数。
<span class = "kwd" > final </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > URL </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "str" > "/volley/resource/all?count=20" </span><span class = "pun" >;</span><span class = "pln" > </span><span class = "typ" >JsonArrayRequest</span><span class = "pln" > req </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >JsonArrayRequest</span><span class = "pun" >(</span><span class = "pln" >URL</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >Listener</span><span class = "pln" > </span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onResponse</span><span class = "pun" >(</span><span class = "typ" >JSONArray</span><span class = "pln" > response</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > try </span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >v</span><span class = "pun" >(</span><span class = "str" > "Response:%n %s" </span><span class = "pun" >,</span><span class = "pln" > response</span><span class = "pun" >.</span><span class = "pln" >toString</span><span class = "pun" >(</span><span class = "lit" > 4 </span><span class = "pun" >));</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > catch </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "typ" >JSONException</span><span class = "pln" > e</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > e</span><span class = "pun" >.</span><span class = "pln" >printStackTrace</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >},</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >ErrorListener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onErrorResponse</span><span class = "pun" >(</span><span class = "typ" >VolleyError</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >e</span><span class = "pun" >(</span><span class = "str" > "Error: " </span><span class = "pun" >,</span><span class = "pln" > error</span><span class = "pun" >.</span><span class = "pln" >getMessage</span><span class = "pun" >());</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >});</span><span class = "pln" > </span><span class = "com" > // add the request object to the queue to be executed</span><span class="pln"> </span><span class = "typ" >ApplicationController</span><span class = "pun" >.</span><span class = "pln" >getInstance</span><span class = "pun" >().</span><span class = "pln" >addToRequestQueue</span><span class = "pun" >(</span><span class = "pln" >req</span><span class = "pun" >);</span> |
StringRequest
这个类可以用来从服务器获取String,如果想自己解析请求响应可以使用这个类,例如返回xml数据。它还可以使用重载的构造函数定制请求。
<span class = "kwd" > final </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > URL </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "str" > "/volley/resource/recent.xml" </span><span class = "pun" >;</span><span class = "pln" > </span><span class = "typ" >StringRequest</span><span class = "pln" > req </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >StringRequest</span><span class = "pun" >(</span><span class = "pln" >URL</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >Listener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onResponse</span><span class = "pun" >(</span><span class = "typ" >String</span><span class = "pln" > response</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >v</span><span class = "pun" >(</span><span class = "str" > "Response:%n %s" </span><span class = "pun" >,</span><span class = "pln" > response</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >},</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >ErrorListener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onErrorResponse</span><span class = "pun" >(</span><span class = "typ" >VolleyError</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyLog</span><span class = "pun" >.</span><span class = "pln" >e</span><span class = "pun" >(</span><span class = "str" > "Error: " </span><span class = "pun" >,</span><span class = "pln" > error</span><span class = "pun" >.</span><span class = "pln" >getMessage</span><span class = "pun" >());</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >});</span><span class = "pln" > </span><span class = "com" > // add the request object to the queue to be executed</span><span class="pln"> </span><span class = "typ" >ApplicationController</span><span class = "pun" >.</span><span class = "pln" >getInstance</span><span class = "pun" >().</span><span class = "pln" >addToRequestQueue</span><span class = "pun" >(</span><span class = "pln" >req</span><span class = "pun" >);</span> |
取消请求
Volley提供了强大的API取消未处理或正在处理的请求。取消请求最简单的方法是调用请求队列cancelAll(tag)的方法,前提是你在添加请求时设置了标记。这样就能使标签标记的请求挂起。
给请求设置标签:
request.setTag("My Tag");
使用ApplicationController添加使用了标签的请求到队列中:
ApplicationController.getInstance().addToRequestQueue(request, "My Tag");
取消所有指定标记的请求:
mRequestQueue.cancelAll("My Tag");
重试失败的请求,自定义请求超时
Volley中没有指定的方法来设置请求超时时间,可以设置RetryPolicy 来变通实现。DefaultRetryPolicy类有个initialTimeout参数,可以设置超时时间。要确保最大重试次数为1,以保证超时后不重新请求。
Setting Request Timeout
1
|
|
如果你想失败后重新请求(因超时),您可以指定使用上面的代码,增加重试次数。注意最后一个参数,它允许你指定一个退避乘数可以用来实现“指数退避”来从RESTful服务器请求数据。
设置请求头(HTTP headers)
有时候需要给HTTP请求添加额外的头信息,一个常用的例子是添加 “Authorization”到HTTP 请求的头信息。Volley请求类提供了一个 getHeaers()的方法,重载这个方法可以自定义HTTP 的头信息。
添加头信息:
<span class = "typ" >JsonObjectRequest</span><span class = "pln" > req </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >JsonObjectRequest</span><span class = "pun" >(</span><span class = "pln" >URL</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >JSONObject</span><span class = "pun" >(</span><span class = "kwd" >params</span><span class = "pun" >),</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >Listener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onResponse</span><span class = "pun" >(</span><span class = "typ" >JSONObject</span><span class = "pln" > response</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // handle response</span><span class="pln"> </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >},</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Response</span><span class = "pun" >.</span><span class = "typ" >ErrorListener</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > onErrorResponse</span><span class = "pun" >(</span><span class = "typ" >VolleyError</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // handle error</span><span class="pln"> </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >})</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "lit" > @Override </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "typ" >Map</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;</span><span class = "pln" > getHeaders</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "kwd" > throws </span><span class = "pln" > </span><span class = "typ" >AuthFailureError</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >HashMap</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;</span><span class = "pln" > headers </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >HashMap</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;();</span><span class = "pln" > headers</span><span class = "pun" >.</span><span class = "pln" >put</span><span class = "pun" >(</span><span class = "str" > "CUSTOM_HEADER" </span><span class = "pun" >,</span><span class = "pln" > </span><span class = "str" > "Yahoo" </span><span class = "pun" >);</span><span class = "pln" > headers</span><span class = "pun" >.</span><span class = "pln" >put</span><span class = "pun" >(</span><span class = "str" > "ANOTHER_CUSTOM_HEADER" </span><span class = "pun" >,</span><span class = "pln" > </span><span class = "str" > "Google" </span><span class = "pun" >);</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > headers</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >};</span> |
使用Cookies
Volley中没有直接的API来设置cookies,Volley的设计理念就是提供干净、简洁的API来实现RESTful HTTP请求,不提供设置cookies是合理的。
下面是修改后的ApplicationController类,这个类修改了getRequestQueue()方法,包含了 设置cookie方法,这些修改还是有些粗糙。
<span class = "com" > // http client instance</span><span class="pln"> </span><span class = "kwd" > private </span><span class = "pln" > </span><span class = "typ" >DefaultHttpClient</span><span class = "pln" > mHttpClient</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "typ" >RequestQueue</span><span class = "pln" > getRequestQueue</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // lazy initialize the request queue, the queue instance will be</span><span class="pln"> </span><span class = "com" > // created when it is accessed for the first time</span><span class="pln"> </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >mRequestQueue </span><span class = "pun" >==</span><span class = "pln" > </span><span class = "kwd" > null </span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // Create an instance of the Http client.</span><span class="pln"> </span><span class = "com" > // We need this in order to access the cookie store</span><span class="pln"> mHttpClient </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >DefaultHttpClient</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "com" > // create the request queue</span><span class="pln"> mRequestQueue </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "typ" >Volley</span><span class = "pun" >.</span><span class = "pln" >newRequestQueue</span><span class = "pun" >(</span><span class = "kwd" > this </span><span class = "pun" >,</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >HttpClientStack</span><span class = "pun" >(</span><span class = "pln" >mHttpClient</span><span class = "pun" >));</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > mRequestQueue</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Method to set a cookie */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > void </span><span class = "pln" > setCookie</span><span class = "pun" >()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >CookieStore</span><span class = "pln" > cs </span><span class = "pun" >=</span><span class = "pln" > mHttpClient</span><span class = "pun" >.</span><span class = "pln" >getCookieStore</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "com" > // create a cookie</span><span class="pln"> cs</span><span class = "pun" >.</span><span class = "pln" >addCookie</span><span class = "pun" >(</span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >BasicClientCookie2</span><span class = "pun" >(</span><span class = "str" > "cookie" </span><span class = "pun" >,</span><span class = "pln" > </span><span class = "str" > "spooky" </span><span class = "pun" >));</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > // add the cookie before adding the request to the queue</span><span class="pln"> setCookie</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "com" > // add the request to the queue</span><span class="pln"> mRequestQueue</span><span class = "pun" >.</span><span class = "pln" >add</span><span class = "pun" >(</span><span class = "pln" >request</span><span class = "pun" >);</span> |
错误处理
正如前面代码看到的,在创建一个请求时,需要添加一个错误监听onErrorResponse。如果请求发生异常,会返回一个VolleyError实例。
以下是Volley的异常列表:
AuthFailureError:如果在做一个HTTP的身份验证,可能会发生这个错误。
NetworkError:Socket关闭,服务器宕机,DNS错误都会产生这个错误。
NoConnectionError:和NetworkError类似,这个是客户端没有网络连接。
ParseError:在使用JsonObjectRequest或JsonArrayRequest时,如果接收到的JSON是畸形,会产生异常。
SERVERERROR:服务器的响应的一个错误,最有可能的4xx或5xx HTTP状态代码。
TimeoutError:Socket超时,服务器太忙或网络延迟会产生这个异常。默认情况下,Volley的超时时间为2.5秒。如果得到这个错误可以使用RetryPolicy。
可以使用一个简单的Help类根据这些异常提示相应的信息:
<span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > class </span><span class = "pln" > </span><span class = "typ" >VolleyErrorHelper</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > /** * Returns appropriate message which is to be displayed to the user * against the specified error object. * * @param error * @param context * @return */ </span><span class = "pln" > </span><span class = "kwd" > public </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > getMessage</span><span class = "pun" >(</span><span class = "typ" >Object</span><span class = "pln" > error</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >Context</span><span class = "pln" > context</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >error </span><span class = "kwd" > instanceof </span><span class = "pln" > </span><span class = "typ" >TimeoutError</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > context</span><span class = "pun" >.</span><span class = "pln" >getResources</span><span class = "pun" >().</span><span class = "pln" >getString</span><span class = "pun" >(</span><span class = "pln" >R</span><span class = "pun" >.</span><span class = "kwd" >string</span><span class = "pun" >.</span><span class = "pln" >generic_server_down</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > else </span><span class = "pln" > </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >isServerProblem</span><span class = "pun" >(</span><span class = "pln" >error</span><span class = "pun" >))</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > handleServerError</span><span class = "pun" >(</span><span class = "pln" >error</span><span class = "pun" >,</span><span class = "pln" > context</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > else </span><span class = "pln" > </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >isNetworkProblem</span><span class = "pun" >(</span><span class = "pln" >error</span><span class = "pun" >))</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > context</span><span class = "pun" >.</span><span class = "pln" >getResources</span><span class = "pun" >().</span><span class = "pln" >getString</span><span class = "pun" >(</span><span class = "pln" >R</span><span class = "pun" >.</span><span class = "kwd" >string</span><span class = "pun" >.</span><span class = "pln" >no_internet</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > context</span><span class = "pun" >.</span><span class = "pln" >getResources</span><span class = "pun" >().</span><span class = "pln" >getString</span><span class = "pun" >(</span><span class = "pln" >R</span><span class = "pun" >.</span><span class = "kwd" >string</span><span class = "pun" >.</span><span class = "pln" >generic_error</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Determines whether the error is related to network * @param error * @return */ </span><span class = "pln" > </span><span class = "kwd" > private </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "kwd" > boolean </span><span class = "pln" > isNetworkProblem</span><span class = "pun" >(</span><span class = "typ" >Object</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >error </span><span class = "kwd" > instanceof </span><span class = "pln" > </span><span class = "typ" >NetworkError</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >||</span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >error </span><span class = "kwd" > instanceof </span><span class = "pln" > </span><span class = "typ" >NoConnectionError</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Determines whether the error is related to server * @param error * @return */ </span><span class = "pln" > </span><span class = "kwd" > private </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "kwd" > boolean </span><span class = "pln" > isServerProblem</span><span class = "pun" >(</span><span class = "typ" >Object</span><span class = "pln" > error</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >error </span><span class = "kwd" > instanceof </span><span class = "pln" > </span><span class = "typ" >ServerError</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >||</span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >error </span><span class = "kwd" > instanceof </span><span class = "pln" > </span><span class = "typ" >AuthFailureError</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > /** * Handles the server error, tries to determine whether to show a stock message or to * show a message retrieved from the server. * * @param err * @param context * @return */ </span><span class = "pln" > </span><span class = "kwd" > private </span><span class = "pln" > </span><span class = "kwd" > static </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pln" > handleServerError</span><span class = "pun" >(</span><span class = "typ" >Object</span><span class = "pln" > err</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >Context</span><span class = "pln" > context</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "typ" >VolleyError</span><span class = "pln" > error </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "pun" >(</span><span class = "typ" >VolleyError</span><span class = "pun" >)</span><span class = "pln" > err</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "typ" >NetworkResponse</span><span class = "pln" > response </span><span class = "pun" >=</span><span class = "pln" > error</span><span class = "pun" >.</span><span class = "pln" >networkResponse</span><span class = "pun" >;</span><span class = "pln" > </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >response </span><span class = "pun" >!=</span><span class = "pln" > </span><span class = "kwd" > null </span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > switch </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >response</span><span class = "pun" >.</span><span class = "pln" >statusCode</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > case </span><span class = "pln" > </span><span class = "lit" > 404 </span><span class = "pun" >:</span><span class = "pln" > </span><span class = "kwd" > case </span><span class = "pln" > </span><span class = "lit" > 422 </span><span class = "pun" >:</span><span class = "pln" > </span><span class = "kwd" > case </span><span class = "pln" > </span><span class = "lit" > 401 </span><span class = "pun" >:</span><span class = "pln" > </span><span class = "kwd" > try </span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "com" > // server might return error like this { "error": "Some error occured" }</span><span class="pln"> </span><span class = "com" > // Use "Gson" to parse the result</span><span class="pln"> </span><span class = "typ" >HashMap</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;</span><span class = "pln" > result </span><span class = "pun" >=</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >Gson</span><span class = "pun" >().</span><span class = "pln" >fromJson</span><span class = "pun" >(</span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >(</span><span class = "pln" >response</span><span class = "pun" >.</span><span class = "pln" >data</span><span class = "pun" >),</span><span class = "pln" > </span><span class = "kwd" > new </span><span class = "pln" > </span><span class = "typ" >TypeToken</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >Map</span><span class = "pun" >&</span><span class = "pln" >lt</span><span class = "pun" >;</span><span class = "typ" >String</span><span class = "pun" >,</span><span class = "pln" > </span><span class = "typ" >String</span><span class = "pun" >&</span><span class = "pln" >gt</span><span class = "pun" >;&</span><span class = "pln" >gt</span><span class = "pun" >;()</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "pun" >}.</span><span class = "pln" >getType</span><span class = "pun" >());</span><span class = "pln" > </span><span class = "kwd" > if </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "pln" >result </span><span class = "pun" >!=</span><span class = "pln" > </span><span class = "kwd" > null </span><span class = "pln" > </span><span class = "pun" >&</span><span class = "pln" >amp</span><span class = "pun" >;&</span><span class = "pln" >amp</span><span class = "pun" >;</span><span class = "pln" > result</span><span class = "pun" >.</span><span class = "pln" >containsKey</span><span class = "pun" >(</span><span class = "str" > "error" </span><span class = "pun" >))</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > result</span><span class = "pun" >.</span><span class = "kwd" >get</span><span class = "pun" >(</span><span class = "str" > "error" </span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > catch </span><span class = "pln" > </span><span class = "pun" >(</span><span class = "typ" >Exception</span><span class = "pln" > e</span><span class = "pun" >)</span><span class = "pln" > </span><span class = "pun" >{</span><span class = "pln" > e</span><span class = "pun" >.</span><span class = "pln" >printStackTrace</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "com" > // invalid request</span><span class="pln"> </span><span class = "kwd" > return </span><span class = "pln" > error</span><span class = "pun" >.</span><span class = "pln" >getMessage</span><span class = "pun" >();</span><span class = "pln" > </span><span class = "kwd" > default </span><span class = "pun" >:</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > context</span><span class = "pun" >.</span><span class = "pln" >getResources</span><span class = "pun" >().</span><span class = "pln" >getString</span><span class = "pun" >(</span><span class = "pln" >R</span><span class = "pun" >.</span><span class = "kwd" >string</span><span class = "pun" >.</span><span class = "pln" >generic_server_down</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "kwd" > return </span><span class = "pln" > context</span><span class = "pun" >.</span><span class = "pln" >getResources</span><span class = "pun" >().</span><span class = "pln" >getString</span><span class = "pun" >(</span><span class = "pln" >R</span><span class = "pun" >.</span><span class = "kwd" >string</span><span class = "pun" >.</span><span class = "pln" >generic_error</span><span class = "pun" >);</span><span class = "pln" > </span><span class = "pun" >}</span><span class = "pln" > </span><span class = "pun" >}</span> |
总结:
Volley是一个非常好的库,你可以尝试使用一下,它会帮助你简化网络请求,带来更多的益处。
我也希望更加全面的介绍Volley,以后可能会介绍使用volley加载图像的内容,欢迎关注。
谢谢你的阅读,希望你能喜欢。
参考:
- NetworkOnMainThreadException —http://developer.android.com/reference/android/os/NetworkOnMainThreadException.html
- Application — http://developer.android.com/reference/android/app/Application.html
原文:
http://arnab.ch/blog/2013/08/asynchronous-http-requests-in-android-using-volley/