Google Volley使用之自定义

PS一句：最终还是选择CSDN来整理发表这几年的知识点，该文章平行迁移到CSDN。因为CSDN也支持MarkDown语法了，牛逼啊！

【工匠若水 http://blog.csdn.net/yanbober】 阅读前一篇《Google Volley使用之基础》 http://blog.csdn.net/yanbober/article/details/45307015

开源项目链接

Volley自定义 Android Developer文档

Volley主页：https://android.googlesource.com/platform/frameworks/volley

Volley仓库：git clone https://android.googlesource.com/platform/frameworks/volley

Volley GitHub Demo：在GitHub主页搜索Volley会有很多，不过建议阅读Android Developer文档。

背景知识

Most requests have ready-to-use implementations in the toolbox; if your response is a string, image, or JSON, you probably won’t need to implement a custom Request.

For cases where you do need to implement a custom request, this is all you need to do:

• Extend the Request class, where represents the type of parsed response the request expects.
  So if your parsed response is a string, for example, create your custom request by extending Request[String].
  See the Volley toolbox classes StringRequest and ImageRequest for examples of extending Request[T].
• Implement the abstract methods parseNetworkResponse() and deliverResponse(), described in more detail below.

正如官方牛逼的说法一样：

你要是请求的是string, image, or JSON还好办，有现成的，前一篇已经详细说明了。But你要是返回的不是这些呢？那就比较蛋疼，需要自定义。不过好的一点是Volley框架的扩展性非常好。所以如果需要customer的话你需要按照如下处理：

• 继承Request[T]类，[T]就是你的响应数据格式。你可以在写customer的时候参考StringRequest实现。
• 实现parseNetworkResponse() and deliverResponse()两个抽象方法。

在StringRequest中，deliverResponse()方法调用了mListener中的onResponse()方法，并将response内容传入。parseNetworkResponse()方法对服务器响应的数据进行解析，数据是字节的形式放在NetworkResponse的data变量中的，这里将数据取出然后组装成一个String，并传入Response的success()方法中。

开搞一个实现

public class GsonRequest<T> extends Request<T> {    private final Gson gson = new Gson();    private final Class<T> clazz;    private final Map<String, String> headers;    private final Listener<T> listener;    /**     * Make a GET request and return a parsed object from JSON.     *     * @param url URL of the request to make     * @param clazz Relevant class object, for Gson's reflection     * @param headers Map of request headers     */    public GsonRequest(String url, Class<T> clazz, Map<String, String> headers,            Listener<T> listener, ErrorListener errorListener) {        super(Method.GET, url, errorListener);        this.clazz = clazz;        this.headers = headers;        this.listener = listener;    }    @Override    public Map<String, String> getHeaders() throws AuthFailureError {        return headers != null ? headers : super.getHeaders();    }    @Override    protected void deliverResponse(T response) {        listener.onResponse(response);    }    @Override    protected Response<T> parseNetworkResponse(NetworkResponse response) {        try {            String json = new String(                    response.data,                    HttpHeaderParser.parseCharset(response.headers));            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));        }    }}

这是官方的GSON的反馈解析实现。

public class XMLRequest extends Request<XmlPullParser> {      private final Listener<XmlPullParser> listener;      public XMLRequest(int method, String url, Listener<XmlPullParser> listener,              ErrorListener errorListener) {          super(method, url, errorListener);          this.listener = listener;      }      public XMLRequest(String url, Listener<XmlPullParser> listener, ErrorListener errorListener) {          this(Method.GET, url, listener, errorListener);      }      @Override     protected Response<XmlPullParser> parseNetworkResponse(NetworkResponse response) {          try {              String xmlString = new String(response.data,                      HttpHeaderParser.parseCharset(response.headers));              XmlPullParserFactory factory = XmlPullParserFactory.newInstance();              XmlPullParser xmlPullParser = factory.newPullParser();              xmlPullParser.setInput(new StringReader(xmlString));              return Response.success(xmlPullParser, HttpHeaderParser.parseCacheHeaders(response));          } catch (UnsupportedEncodingException e) {              return Response.error(new ParseError(e));          } catch (XmlPullParserException e) {              return Response.error(new ParseError(e));          }      }      @Override     protected void deliverResponse(XmlPullParser response) {          listener.onResponse(response);      }  }

这是一个XmlPullParser反馈解析的实现。

通过如上你会发现Volley框架不愧于是Google大牛搞的，连拓展自定义都这么方便，设计模式运用的出神入化，膜拜。

【工匠若水 http://blog.csdn.net/yanbober】 继续阅读《 Google Volley框架源码走读》 http://blog.csdn.net/yanbober/article/details/45307217