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之前讲了ym—— Android网络框架Volley(体验篇)，大家应该了解了volley的使用，接下来我们要看看如何把volley使用到实战项目里面，我们先考虑下一些问题：
从上一篇来看mQueue 只需要一个对象即可，new RequestQueue对象对资源一种浪费，我们应该在application，以及可以把取消请求的方法也在application进行统一管理，看以下代码：
package com.chronocloud.lib.base;import android.app.Application;import android.text.TextUtils;import com.android.volley.Request;import com.android.volley.RequestQueue;import com.android.volley.VolleyLog;import com.android.volley.toolbox.Volley;public class ApplicationController extends Application {/** * Log or request TAG */public static final String TAG = "VolleyPatterns";/** * Global request queue for Volley */private RequestQueue mRequestQueue;/** * A singleton instance of the application class for easy access in other * places */private static ApplicationController sInstance;@Overridepublic void onCreate() {super.onCreate();// initialize the singletonsInstance = this;}/** * @return ApplicationController singleton instance */public static synchronized ApplicationController getInstance() {return sInstance;}/** * @return The Volley Request queue, the queue will be created if it is null */public RequestQueue getRequestQueue() {// lazy initialize the request queue, the queue instance will be// created when it is accessed for the first timeif (mRequestQueue == null) {// 1// 2synchronized (ApplicationController.class) {if (mRequestQueue == null) {mRequestQueue = Volley.newRequestQueue(getApplicationContext());}}}return mRequestQueue;}/** * 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 */public <T> void addToRequestQueue(Request<T> req, String tag) {// set the default tag if tag is emptyreq.setTag(TextUtils.isEmpty(tag) ? TAG : tag);VolleyLog.d("Adding request to queue: %s", req.getUrl());getRequestQueue().add(req);}/** * Adds the specified request to the global queue using the Default TAG. * * @param req * @param tag */public <T> void addToRequestQueue(Request<T> req) {// set the default tag if tag is emptyreq.setTag(TAG);getRequestQueue().add(req);}/** * 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 */public void cancelPendingRequests(Object tag) {if (mRequestQueue != null) {mRequestQueue.cancelAll(tag);}}}
接下来我们来看看，如何自定义Request
XmlRequest：
public class XMLRequest extends Request<XmlPullParser> {private final Listener<XmlPullParser> mListener;public XMLRequest(int method, String url, Listener<XmlPullParser> listener,ErrorListener errorListener) {super(method, url, errorListener);mListener = listener;}public XMLRequest(String url, Listener<XmlPullParser> listener, ErrorListener errorListener) {this(Method.GET, url, listener, errorListener);}@Overrideprotected 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));}}@Overrideprotected void deliverResponse(XmlPullParser response) {mListener.onResponse(response);}}GsonRequest（注意需要自行导入gson.jar）：public class GsonRequest<T> extends Request<T> {private final Listener<T> mListener;private Gson mGson;private Class<T> mClass;public GsonRequest(int method, String url, Class<T> clazz, Listener<T> listener,ErrorListener errorListener) {super(method, url, errorListener);mGson = new Gson();mClass = clazz;mListener = listener;}public GsonRequest(String url, Class<T> clazz, Listener<T> listener,ErrorListener errorListener) {this(Method.GET, url, clazz, listener, errorListener);}@Overrideprotected Response<T> parseNetworkResponse(NetworkResponse response) {try {String jsonString = new String(response.data,HttpHeaderParser.parseCharset(response.headers));return Response.success(mGson.fromJson(jsonString, mClass),HttpHeaderParser.parseCacheHeaders(response));} catch (UnsupportedEncodingException e) {return Response.error(new ParseError(e));}}@Overrideprotected void deliverResponse(T response) {mListener.onResponse(response);}}接下只差最后一步了就是封装它的错误处理，使用过volley的都知道，volley的监听错误提示都是NoConnectionError。。。等等，这类的错误提示，显然这不是我们想给用户呈现的错误提示，因为就算提示了用户也不明白什么意思，所以我们还要封装一下，能让用户看的更清楚的理解这些错误提示。ym—— Android网络框架Volley(体验篇)我们讲过每个请求都需要设置一个失败的监听：// 共用失败回调private class StrErrListener implements ErrorListener {@Overridepublic void onErrorResponse(VolleyError arg0) {Toast.makeText(mContext,VolleyErrorHelper.getMessage(arg0, mContext),Toast.LENGTH_LONG).show();}}以上代码有个VolleyError对象，我们可以从这个对象上下手：package com.example.volley;import java.util.HashMap;import java.util.Map;import android.content.Context;import com.android.volley.AuthFailureError;import com.android.volley.NetworkError;import com.android.volley.NetworkResponse;import com.android.volley.NoConnectionError;import com.android.volley.ServerError;import com.android.volley.TimeoutError;import com.android.volley.VolleyError;import com.google.gson.Gson;import com.google.gson.reflect.TypeToken;//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。public class VolleyErrorHelper {/** * Returns appropriate message which is to be displayed to the user against * the specified error object. * * @param error * @param context * @return */public static String getMessage(Object error, Context context) {if (error instanceof TimeoutError) {return context.getResources().getString(R.string.generic_server_down);} else if (isServerProblem(error)) {return handleServerError(error, context);} else if (isNetworkProblem(error)) {return context.getResources().getString(R.string.no_internet);}return context.getResources().getString(R.string.generic_error);}/** * Determines whether the error is related to network * * @param error * @return */private static boolean isNetworkProblem(Object error) {return (error instanceof NetworkError)|| (error instanceof NoConnectionError);}/** * Determines whether the error is related to server * * @param error * @return */private static boolean isServerProblem(Object error) {return (error instanceof ServerError)|| (error instanceof AuthFailureError);}/** * 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 */private static String handleServerError(Object err, Context context) {VolleyError error = (VolleyError) err;NetworkResponse response = error.networkResponse;if (response != null) {switch (response.statusCode) {case 404:case 422:case 401:try {// server might return error like this { "error":// "Some error occured" }// Use "Gson" to parse the resultHashMap<String, String> result = new Gson().fromJson(new String(response.data),new TypeToken<Map<String, String>>() {}.getType());if (result != null && result.containsKey("error")) {return result.get("error");}} catch (Exception e) {e.printStackTrace();}// invalid requestreturn error.getMessage();default:return context.getResources().getString(R.string.generic_server_down);}}return context.getResources().getString(R.string.generic_error);}}以上代码中引用的xml是：<string name="no_internet">无网络连接~！</string><string name="generic_server_down">连接服务器失败~！</string><string name="generic_error">网络异常,请稍后再试~！</string>接下来，数据请求这一块已经说完了，我们来说下图片这一块，，我个人喜欢使用universal-image-loader而不是volley自己提供的（个人认为使用起来universal-image-loader更便捷一些）。好啦讲完了，大家可以去实战开发了~！不懂或者遇到问题的可以留言讨论~！
发光并非太阳的专利，我也可以发光 。
