详细解读Volley（一）—— 基本Request对象 & RequestQueue&请求取消
Volley它非常适合去进行数据量不大，但通信频繁的网络操作，而对于大数据量的网络操作，比如说下载文件等，Volley的表现就会非常糟糕。 所以不建议用它去进行下载文件、加载大图的操作。有人可能会问，如果我服务器中的图片都挺大的，activity中listview要加载这些图片，是不 是不能用这个框架呢？其实这个问题本身就是错误的，你想如果你服务器的图片都是大图，你要在手机上用照片墙进行展示，下载图片都会慢的要死，这个本身就是 不可行的。所以在项目初期就应该建立好服务器端的小图，照片墙用加载小图，点击后再从网络上下载大图，这才是正确思路。这时你就可以用volley加载小 图了，如果是要加载大图，可以用别的算法，强烈建议手动完成大图清除的工作，否则很可能会出现OOM。Volley本身没有做什么回收算法，还是用最基本 的GC，实际使用中可以根据需要自定义一下。
零、准备工作
Git项目，添加为lib，申请权限
git clone https://android.googlesource.com/platform/frameworks/volley
<uses-permission android:name="android.permission.INTERNET" />
一、初始化请求对象——RequestQueue
public class MyApplication extends Application {
public static RequestQueue requestQueue;
@Override
public void onCreate() {
super.onCreate();
// 不必为每一次HTTP请求都创建一个RequestQueue对象，推荐在application中初始化
requestQueue = Volley.newRequestQueue(this);
}
}
既然是Http操作，自然有请求和响应，RequestQueue是一个请求队列 对象，它可以缓存所有的HTTP请求，然后按照一定的算法并发地发出这些请求。RequestQueue内部的设计就是非常合适高并发的，因此我们不必为 每一次HTTP请求都创建一个RequestQueue对象，这是非常浪费资源的。所以在这里我建立了一个application，然后用单例模式定义了 这个对象。当然，你可以选择在一个activity中定义一个RequestQueue对象，但这样可能会比较麻烦，而且还可能出现请求队列包含 activity强引用的问题，因此我还是推荐在application中定义。
二、使用StringRequest接收String类型的响应
前 面定义了请求对象，那么自然就有接收响应的对象了，这个框架中有多个响应对象，像StringRequest接受到的响应就是string类型 的；JsonRequest接收的响应就是Json类型对象。其实它们都是继承自Request<T>，然后根据不同的响应数据来进行特殊的 处理。
2.1 初始化
/**
* Creates a new request with the given method.
*
* @param method the request {@link Method} to use
* @param url URL to fetch the string at
* @param listener Listener to receive the String response
* @param errorListener Error listener, or null to ignore errors
*/
public StringRequest(int method, String url, Listener<String> listener, ErrorListener errorListener)
/**
* Creates a new GET request.
*
* @param url URL to fetch the string at
* @param listener Listener to receive the String response
* @param errorListener Error listener, or null to ignore errors
*/
public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
this(Method.GET, url, listener, errorListener);
}
这就是StringRequest的两个构造函数，不同之处是一个传入了一个method的参数，一个没有。其实看上面的源码就知道，如果你不传入method，默认会调用GET方式进行请求。当你传入了Method.POST就会用post来请求。
【参数解释】
url：请求的地址
listener：响应成功的监听器
errorListener：出错时的监听器
StringRequest getStringRequest = new StringRequest("http://www.baidu.com", new ResponseListener(), new ResponseErrorListener());
StringRequest postStringRequest = new StringRequest(Method.POST, "http://www.baidu.com", new ResponseListener(),null);
2.2 配置监听器
/**
* @author:Jack Tony
* @description :设置响应结果监听器，因为用的是StringRequest，所以这里的结果我定义为string类型
* @date :2015年1月24日
*/
private class ResponseListener implements Response.Listener<String>{
@Override
public void onResponse(String response) {
// TODO 自动生成的方法存根
Log.d("TAG", "-------------
" + response);
}
}
/**
* @author:Jack Tony
* @description :访问出错时触发的监听器
* @date :2015年1月28日
*/
private class ResponseErrorListener implements Response.ErrorListener{
@Override
public void onErrorResponse(VolleyError error) {
// TODO 自动生成的方法存根
Log.e("TAG", error.getMessage(), error);
}
}
这两个监听器没啥可说的，因为是StringRequest调用的，所以成功时触发的监听器中得到的response就是String类型。如果访问出错，那么就打印出错信息。
2.3 执行GET请求
现在我们有了请求对象和响应对象，外加处理响应结果的监听器，那么就执行最后一步——发送请求。发送请求很简单，将响应对象添加到请求队列即可。
mQueue.add(getStringRequest);
完整代码：
RequestQueue mQueue = MyApplication.requestQueue;
StringRequest getStringRequest = new StringRequest("http://www.baidu.com", new ResponseListener(), new ResponseErrorListener());
mQueue.add(getStringRequest);
通过简单的add()方法就直接发送了请求，如果服务器响应了请求就会触发我们的结果监听器，然后被打印出啦。现在请求的是百度，所以得到了网页的源码：
2.4 执行POST请求
POST和GET一样，仅仅是传入的方法不同。但一般我们的post都是要带一些参数的，volley没有提供附加参数的方法，所以我们必须要在StringRequest的匿名类中重写getParams()方法：
StringRequest stringRequest = new StringRequest(Method.POST, url, listener, errorListener) {
@Override
protected Map<String, String> getParams() throws AuthFailureError {
Map<String, String> map = new HashMap<String, String>();
map.put("params1", "value1");
map.put("params2", "value2");
return map;
}
};
这 样就传入了value1和value2两个参数了。现在可能有人会问为啥这个框架不提供这个传参的方法，还非得让我们重写。我个人觉得这个框架本身的目的 就是执行频繁的网络请求，比如下载图片，解析json数据什么的，用GET就能很好的实现了，所以就没有提供传参的POST方法。为了简单起见，我重写了 Request类中的getParams()，添加了传参的方法，以后通过setParams()就可以传参数了。
重写的代码块：
Map<String, String> mParams = null;
/**
* Returns a Map of parameters to be used for a POST or PUT request. Can throw
* {@link AuthFailureError} as authentication may be required to provide these values.
*
* <p>Note that you can directly override {@link #getBody()} for custom data.</p>
*
* @throws AuthFailureError in the event of auth failure
*/
protected Map<String, String> getParams() throws AuthFailureError {
return mParams;
}
public void setParams(Map<String, String> params){
mParams = params;
}
完整代码：
/* * Copyright (C) 2011 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.android.volley; import java.io.UnsupportedEncodingException; import java.net.URLEncoder; import java.util.Collections; import java.util.Map; import android.net.TrafficStats; import android.net.Uri; import android.os.Handler; import android.os.Looper; import android.os.SystemClock; import android.text.TextUtils; import com.android.volley.VolleyLog.MarkerLog; /** * Base class for all network requests. * * @param <T> The type of parsed response this request expects. */ public abstract class Request<T> implements Comparable<Request<T>> { /** * Default encoding for POST or PUT parameters. See {@link #getParamsEncoding()}. */ private static final String DEFAULT_PARAMS_ENCODING = "UTF-8"; /** * Supported request methods. */ public interface Method { int DEPRECATED_GET_OR_POST = -1; int GET = 0; int POST = 1; int PUT = 2; int DELETE = 3; int HEAD = 4; int OPTIONS = 5; int TRACE = 6; int PATCH = 7; } /** An event log tracing the lifetime of this request; for debugging. */ private final MarkerLog mEventLog = MarkerLog.ENABLED ? new MarkerLog() : null; /** * Request method of this request. Currently supports GET, POST, PUT, DELETE, HEAD, OPTIONS, * TRACE, and PATCH. */ private final int mMethod; /** URL of this request. */ private final String mUrl; /** Default tag for {@link TrafficStats}. */ private final int mDefaultTrafficStatsTag; /** Listener interface for errors. */ private final Response.ErrorListener mErrorListener; /** Sequence number of this request, used to enforce FIFO ordering. */ private Integer mSequence; /** The request queue this request is associated with. */ private RequestQueue mRequestQueue; /** Whether or not responses to this request should be cached. */ private boolean mShouldCache = true; /** Whether or not this request has been canceled. */ private boolean mCanceled = false; /** Whether or not a response has been delivered for this request yet. */ private boolean mResponseDelivered = false; // A cheap variant of request tracing used to dump slow requests. private long mRequestBirthTime = 0; /** Threshold at which we should log the request (even when debug logging is not enabled). */ private static final long SLOW_REQUEST_THRESHOLD_MS = 3000; /** The retry policy for this request. */ private RetryPolicy mRetryPolicy; /** * When a request can be retrieved from cache but must be refreshed from * the network, the cache entry will be stored here so that in the event of * a "Not Modified" response, we can be sure it hasn't been evicted from cache. */ private Cache.Entry mCacheEntry = null; /** An opaque token tagging this request; used for bulk cancellation. */ private Object mTag; /** * Creates a new request with the given URL and error listener. Note that * the normal response listener is not provided here as delivery of responses * is provided by subclasses, who have a better idea of how to deliver an * already-parsed response. * * @deprecated Use {@link #Request(int, String, com.android.volley.Response.ErrorListener)}. */ @Deprecated public Request(String url, Response.ErrorListener listener) { this(Method.DEPRECATED_GET_OR_POST, url, listener); } /** * Creates a new request with the given method (one of the values from {@link Method}), * URL, and error listener. Note that the normal response listener is not provided here as * delivery of responses is provided by subclasses, who have a better idea of how to deliver * an already-parsed response. */ public Request(int method, String url, Response.ErrorListener listener) { mMethod = method; mUrl = url; mErrorListener = listener; setRetryPolicy(new DefaultRetryPolicy()); mDefaultTrafficStatsTag = findDefaultTrafficStatsTag(url); } /** * Return the method for this request. Can be one of the values in {@link Method}. */ public int getMethod() { return mMethod; } /** * Set a tag on this request. Can be used to cancel all requests with this * tag by {@link RequestQueue#cancelAll(Object)}. * * @return This Request object to allow for chaining. */ public Request<?> setTag(Object tag) { mTag = tag; return this; } /** * Returns this request's tag. * @see Request#setTag(Object) */ public Object getTag() { return mTag; } /** * @return this request's {@link com.android.volley.Response.ErrorListener}. */ public Response.ErrorListener getErrorListener() { return mErrorListener; } /** * @return A tag for use with {@link TrafficStats#setThreadStatsTag(int)} */ public int getTrafficStatsTag() { return mDefaultTrafficStatsTag; } /** * @return The hashcode of the URL's host component, or 0 if there is none. */ private static int findDefaultTrafficStatsTag(String url) { if (!TextUtils.isEmpty(url)) { Uri uri = Uri.parse(url); if (uri != null) { String host = uri.getHost(); if (host != null) { return host.hashCode(); } } } return 0; } /** * Sets the retry policy for this request. * * @return This Request object to allow for chaining. */ public Request<?> setRetryPolicy(RetryPolicy retryPolicy) { mRetryPolicy = retryPolicy; return this; } /** * Adds an event to this request's event log; for debugging. */ public void addMarker(String tag) { if (MarkerLog.ENABLED) { mEventLog.add(tag, Thread.currentThread().getId()); } else if (mRequestBirthTime == 0) { mRequestBirthTime = SystemClock.elapsedRealtime(); } } /** * Notifies the request queue that this request has finished (successfully or with error). * * <p>Also dumps all events from this request's event log; for debugging.</p> */ void finish(final String tag) { if (mRequestQueue != null) { mRequestQueue.finish(this); } if (MarkerLog.ENABLED) { final long threadId = Thread.currentThread().getId(); if (Looper.myLooper() != Looper.getMainLooper()) { // If we finish marking off of the main thread, we need to // actually do it on the main thread to ensure correct ordering. Handler mainThread = new Handler(Looper.getMainLooper()); mainThread.post(new Runnable() { @Override public void run() { mEventLog.add(tag, threadId); mEventLog.finish(this.toString()); } }); return; } mEventLog.add(tag, threadId); mEventLog.finish(this.toString()); } else { long requestTime = SystemClock.elapsedRealtime() - mRequestBirthTime; if (requestTime >= SLOW_REQUEST_THRESHOLD_MS) { VolleyLog.d("%d ms: %s", requestTime, this.toString()); } } } /** * Associates this request with the given queue. The request queue will be notified when this * request has finished. * * @return This Request object to allow for chaining. */ public Request<?> setRequestQueue(RequestQueue requestQueue) { mRequestQueue = requestQueue; return this; } /** * Sets the sequence number of this request. Used by {@link RequestQueue}. * * @return This Request object to allow for chaining. */ public final Request<?> setSequence(int sequence) { mSequence = sequence; return this; } /** * Returns the sequence number of this request. */ public final int getSequence() { if (mSequence == null) { throw new IllegalStateException("getSequence called before setSequence"); } return mSequence; } /** * Returns the URL of this request. */ public String getUrl() { return mUrl; } /** * Returns the cache key for this request. By default, this is the URL. */ public String getCacheKey() { return getUrl(); } /** * Annotates this request with an entry retrieved for it from cache. * Used for cache coherency support. * * @return This Request object to allow for chaining. */ public Request<?> setCacheEntry(Cache.Entry entry) { mCacheEntry = entry; return this; } /** * Returns the annotated cache entry, or null if there isn't one. */ public Cache.Entry getCacheEntry() { return mCacheEntry; } /** * Mark this request as canceled. No callback will be delivered. */ public void cancel() { mCanceled = true; } /** * Returns true if this request has been canceled. */ public boolean isCanceled() { return mCanceled; } /** * Returns a list of extra HTTP headers to go along with this request. Can * throw {@link AuthFailureError} as authentication may be required to * provide these values. * @throws AuthFailureError In the event of auth failure */ public Map<String, String> getHeaders() throws AuthFailureError { return Collections.emptyMap(); } /** * Returns a Map of POST parameters to be used for this request, or null if * a simple GET should be used. Can throw {@link AuthFailureError} as * authentication may be required to provide these values. * * <p>Note that only one of getPostParams() and getPostBody() can return a non-null * value.</p> * @throws AuthFailureError In the event of auth failure * * @deprecated Use {@link #getParams()} instead. */ @Deprecated protected Map<String, String> getPostParams() throws AuthFailureError { return getParams(); } /** * Returns which encoding should be used when converting POST parameters returned by * {@link #getPostParams()} into a raw POST body. * * <p>This controls both encodings: * <ol> * <li>The string encoding used when converting parameter names and values into bytes prior * to URL encoding them.</li> * <li>The string encoding used when converting the URL encoded parameters into a raw * byte array.</li> * </ol> * * @deprecated Use {@link #getParamsEncoding()} instead. */ @Deprecated protected String getPostParamsEncoding() { return getParamsEncoding(); } /** * @deprecated Use {@link #getBodyContentType()} instead. */ @Deprecated public String getPostBodyContentType() { return getBodyContentType(); } /** * Returns the raw POST body to be sent. * * @throws AuthFailureError In the event of auth failure * * @deprecated Use {@link #getBody()} instead. */ @Deprecated public byte[] getPostBody() throws AuthFailureError { // Note: For compatibility with legacy clients of volley, this implementation must remain // here instead of simply calling the getBody() function because this function must // call getPostParams() and getPostParamsEncoding() since legacy clients would have // overridden these two member functions for POST requests. Map<String, String> postParams = getPostParams(); if (postParams != null && postParams.size() > 0) { return encodeParameters(postParams, getPostParamsEncoding()); } return null; } Map<String, String> mParams = null; /** * Returns a Map of parameters to be used for a POST or PUT request. Can throw * {@link AuthFailureError} as authentication may be required to provide these values. * * <p>Note that you can directly override {@link #getBody()} for custom data.</p> * * @throws AuthFailureError in the event of auth failure */ protected Map<String, String> getParams() throws AuthFailureError { return mParams; } public void setParams(Map<String, String> params){ mParams = params; } /** * Returns which encoding should be used when converting POST or PUT parameters returned by * {@link #getParams()} into a raw POST or PUT body. * * <p>This controls both encodings: * <ol> * <li>The string encoding used when converting parameter names and values into bytes prior * to URL encoding them.</li> * <li>The string encoding used when converting the URL encoded parameters into a raw * byte array.</li> * </ol> */ protected String getParamsEncoding() { return DEFAULT_PARAMS_ENCODING; } /** * Returns the content type of the POST or PUT body. */ public String getBodyContentType() { return "application/x-www-form-urlencoded; charset=" + getParamsEncoding(); } /** * Returns the raw POST or PUT body to be sent. * * <p>By default, the body consists of the request parameters in * application/x-www-form-urlencoded format. When overriding this method, consider overriding * {@link #getBodyContentType()} as well to match the new body format. * * @throws AuthFailureError in the event of auth failure */ public byte[] getBody() throws AuthFailureError { Map<String, String> params = getParams(); if (params != null && params.size() > 0) { return encodeParameters(params, getParamsEncoding()); } return null; } /** * Converts <code>params</code> into an application/x-www-form-urlencoded encoded string. */ private byte[] encodeParameters(Map<String, String> params, String paramsEncoding) { StringBuilder encodedParams = new StringBuilder(); try { for (Map.Entry<String, String> entry : params.entrySet()) { encodedParams.append(URLEncoder.encode(entry.getKey(), paramsEncoding)); encodedParams.append('='); encodedParams.append(URLEncoder.encode(entry.getValue(), paramsEncoding)); encodedParams.append('&'); } return encodedParams.toString().getBytes(paramsEncoding); } catch (UnsupportedEncodingException uee) { throw new RuntimeException("Encoding not supported: " + paramsEncoding, uee); } } /** * Set whether or not responses to this request should be cached. * * @return This Request object to allow for chaining. */ public final Request<?> setShouldCache(boolean shouldCache) { mShouldCache = shouldCache; return this; } /** * Returns true if responses to this request should be cached. */ public final boolean shouldCache() { return mShouldCache; } /** * Priority values. Requests will be processed from higher priorities to * lower priorities, in FIFO order. */ public enum Priority { LOW, NORMAL, HIGH, IMMEDIATE } /** * Returns the {@link Priority} of this request; {@link Priority#NORMAL} by default. */ public Priority getPriority() { return Priority.NORMAL; } /** * Returns the socket timeout in milliseconds per retry attempt. (This value can be changed * per retry attempt if a backoff is specified via backoffTimeout()). If there are no retry * attempts remaining, this will cause delivery of a {@link TimeoutError} error. */ public final int getTimeoutMs() { return mRetryPolicy.getCurrentTimeout(); } /** * Returns the retry policy that should be used for this request. */ public RetryPolicy getRetryPolicy() { return mRetryPolicy; } /** * Mark this request as having a response delivered on it. This can be used * later in the request's lifetime for suppressing identical responses. */ public void markDelivered() { mResponseDelivered = true; } /** * Returns true if this request has had a response delivered for it. */ public boolean hasHadResponseDelivered() { return mResponseDelivered; } /** * Subclasses must implement this to parse the raw network response * and return an appropriate response type. This method will be * called from a worker thread. The response will not be delivered * if you return null. * @param response Response from the network * @return The parsed response, or null in the case of an error */ abstract protected Response<T> parseNetworkResponse(NetworkResponse response); /** * Subclasses can override this method to parse 'networkError' and return a more specific error. * * <p>The default implementation just returns the passed 'networkError'.</p> * * @param volleyError the error retrieved from the network * @return an NetworkError augmented with additional information */ protected VolleyError parseNetworkError(VolleyError volleyError) { return volleyError; } /** * Subclasses must implement this to perform delivery of the parsed * response to their listeners. The given response is guaranteed to * be non-null; responses that fail to parse are not delivered. * @param response The parsed response returned by * {@link #parseNetworkResponse(NetworkResponse)} */ abstract protected void deliverResponse(T response); /** * Delivers error message to the ErrorListener that the Request was * initialized with. * * @param error Error details */ public void deliverError(VolleyError error) { if (mErrorListener != null) { mErrorListener.onErrorResponse(error); } } /** * Our comparator sorts from high to low priority, and secondarily by * sequence number to provide FIFO ordering. */ @Override public int compareTo(Request<T> other) { Priority left = this.getPriority(); Priority right = other.getPriority(); // High-priority requests are "lesser" so they are sorted to the front. // Equal priorities are sorted by sequence number to provide FIFO ordering. return left == right ? this.mSequence - other.mSequence : right.ordinal() - left.ordinal(); } @Override public String toString() { String trafficStatsTag = "0x" + Integer.toHexString(getTrafficStatsTag()); return (mCanceled ? "[X] " : "[ ] ") + getUrl() + " " + trafficStatsTag + " " + getPriority() + " " + mSequence; } }
使用示例：
StringRequest postStringRequest = new StringRequest(Method.POST, "http://m.weather.com.cn/data/101010100.html",
new ResponseListener(), null);
Map<String, String> map = new HashMap<String, String>();
map.put("params1", "value1");
map.put("params2", "value2");
postStringRequest.setParams(map);
mQueue.add(postStringRequest);
结果：
三、使用JsonObjectRequest接收Json类型的响应
类似于StringRequest，JsonRequest也是继承自Request类的，不过由于JsonRequest是一个抽象类，因此我们无法直接创建它的实例，那么只能从它的子类入手了。JsonRequest有两个直接的子类，JsonObjectRequest和JsonArrayRequest，从名字上你应该能就看出它们的区别了吧？一个是用于请求一段JSON数据的，一个是用于请求一段JSON数组的。
3.1 构造函数
/**
* Creates a new request.
* @param method the HTTP method to use
* @param url URL to fetch the JSON from
* @param jsonRequest A {@link JSONObject} to post with the request. Null is allowed and
* indicates no parameters will be posted along with request.
* @param listener Listener to receive the JSON response
* @param errorListener Error listener, or null to ignore errors.
*/
public JsonObjectRequest(int method, String url, JSONObject jsonRequest,
Listener<JSONObject> listener, ErrorListener errorListener) {
super(method, url, (jsonRequest == null) ? null : jsonRequest.toString(), listener,
errorListener);
}
/**
* Constructor which defaults to <code>GET</code> if <code>jsonRequest</code> is
* <code>null</code>, <code>POST</code> otherwise.
*
* @see #JsonObjectRequest(int, String, JSONObject, Listener, ErrorListener)
*/
public JsonObjectRequest(String url, JSONObject jsonRequest, Listener<JSONObject> listener,
ErrorListener errorListener) {
this(jsonRequest == null ? Method.GET : Method.POST, url, jsonRequest,
listener, errorListener);
}
3.2 发送请求
和之前讲过的StringRequest一样，可以传入请求的类型，如果没传就默认是GET请求。参数也是如出一辙，就是泛型变了下。定义和使用的方式也完全一致，初始化对象后，添加到请求队列即可。
JsonObjectRequest request = new JsonObjectRequest("http://m.weather.com.cn/data/101010100.html",
null, new ResponseListener(), new ResponseErrorListener());
mQueue.add(request);
/**
* @author:Jack Tony
* @description :设置响应结果监听器，这里用的是JsonObjectRequest，所以返回的结果是JSONObject
* @date :2015年1月24日
*/
private class ResponseListener implements Response.Listener<JSONObject> {
@Override
public void onResponse(JSONObject response) {
// TODO 自动生成的方法存根
Log.d("TAG", "-------------
" + response.toString());
}
}
/**
* @author:Jack Tony
* @description :访问出错时触发的监听器
* @date :2015年1月28日
*/
private class ResponseErrorListener implements Response.ErrorListener {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("TAG", error.getMessage(), error);
}
}
结果：
你怎么查看解析是否成功了呢？服务器端的数据：
{"weatherinfo":{"city":"北京","city_en":"beijing","date_y":"2014年3月4日","date":"","week":"星期二","fchh":"11","cityid":"101010100","temp1":"8℃~-3℃","temp2":"8℃~-3℃","temp3":"7℃~-3℃","temp4":"8℃~-1℃","temp5":"10℃~1℃","temp6":"10℃~2℃","tempF1":"46.4℉~26.6℉","tempF2":"46.4℉~26.6℉","tempF3":"44.6℉~26.6℉","tempF4":"46.4℉~30.2℉","tempF5":"50℉~33.8℉","tempF6":"50℉~35.6℉","weather1":"晴","weather2":"晴","weather3":"晴","weather4":"晴转多云","weather5":"多云","weather6":"多云","img1":"0","img2":"99","img3":"0","img4":"99","img5":"0","img6":"99","img7":"0","img8":"1","img9":"1","img10":"99","img11":"1","img12":"99","img_single":"0","img_title1":"晴","img_title2":"晴","img_title3":"晴","img_title4":"晴","img_title5":"晴","img_title6":"晴","img_title7":"晴","img_title8":"多云","img_title9":"多云","img_title10":"多云","img_title11":"多云","img_title12":"多云","img_title_single":"晴","wind1":"北风4-5级转微风","wind2":"微风","wind3":"微风","wind4":"微风","wind5":"微风","wind6":"微风","fx1":"北风","fx2":"微风","fl1":"4-5级转小于3级","fl2":"小于3级","fl3":"小于3级","fl4":"小于3级","fl5":"小于3级","fl6":"小于3级","index":"寒冷","index_d":"天气寒冷，建议着厚羽绒服、毛皮大衣加厚毛衣等隆冬服装。年老体弱者尤其要注意保暖防冻。","index48":"冷","index48_d":"天气冷，建议着棉服、羽绒服、皮夹克加羊毛衫等冬季服装。年老体弱者宜着厚棉衣、冬大衣或厚羽绒服。","index_uv":"中等","index48_uv":"中等","index_xc":"较适宜","index_tr":"一般","index_co":"较舒适","st1":"7","st2":"-3","st3":"8","st4":"0","st5":"7","st6":"-1","index_cl":"较不宜","index_ls":"基本适宜","index_ag":"易发"}}
如果解析错误，就会出现警告，这时错误监听器就会被触发：
如果解析成功，就不会出现错误，这就是泛型的好处，保证了程序的正确性。
最终我们就可以在Response.Listener<JSONObject>中得到JSONObject对象，通过这个对象就能进行下一步的处理了。
3.3 解析Json
比如要解析出上面Json数据中city的字段，就可以按照如下方式编码：
try {
response = response.getJSONObject("weatherinfo");
Log.i(TAG, "City = " + response.getString("city"));
} catch (JSONException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
完整监听器代码：
private class ResponseListener implements Response.Listener<JSONObject> {
@Override
public void onResponse(JSONObject response) {
// TODO 自动生成的方法存根
Log.d("TAG", "-------------
" + response.toString());
try {
response = response.getJSONObject("weatherinfo");
Log.i(TAG, "City = " + response.getString("city"));
} catch (JSONException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
}
结果：
四、JsonArrayRequest简介
除此之外，还有一个相关的响应对象叫做JsonArrayRequest，这个获得的就是一个Json序列，使用方式没有任何改变，这里就不做过多介绍了，因为剩下的就是Json的知识了，和Volley没有任何关系。
源码：
/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.volley.toolbox;
import com.android.volley.NetworkResponse;
import com.android.volley.ParseError;
import com.android.volley.Response;
import com.android.volley.Response.ErrorListener;
import com.android.volley.Response.Listener;
import org.json.JSONArray;
import org.json.JSONException;
import java.io.UnsupportedEncodingException;
/**
* A request for retrieving a {@link JSONArray} response body at a given URL.
*/
public class JsonArrayRequest extends JsonRequest<JSONArray> {
/**
* Creates a new request.
* @param url URL to fetch the JSON from
* @param listener Listener to receive the JSON response
* @param errorListener Error listener, or null to ignore errors.
*/
public JsonArrayRequest(String url, Listener<JSONArray> listener, ErrorListener errorListener) {
super(Method.GET, url, null, listener, errorListener);
}
@Override
protected Response<JSONArray> parseNetworkResponse(NetworkResponse response) {
try {
String jsonString =
new String(response.data, HttpHeaderParser.parseCharset(response.headers));
return Response.success(new JSONArray(jsonString),
HttpHeaderParser.parseCacheHeaders(response));
} catch (UnsupportedEncodingException e) {
return Response.error(new ParseError(e));
} catch (JSONException je) {
return Response.error(new ParseError(je));
}
}
}
通过源码我们知道，这个响应对象发送的请求是Get，而且它是继承自JsonRequest，如果你想用POST来做，自行添加新的构造函数即可。
四、请求取消
Activity里面启动了网络请求，而在这个网络请求还没返回结果的时候，Activity被结束了，此时如果继续使用其中的Context等，除了无辜的浪费CPU，电池，网络等资源，有可能还会导致程序crash，所以，我们需要处理这种一场情况。使用Volley的话，我们可以在Activity停止的时候，同时取消所有或部分未完成的网络请求。Volley里所有的请求结果会返回给主进程，如果在主进程里取消了某些请求，则这些请求将不会被返回给主线程。Volley支持多种request取消方式。
1）可以针对某些个request做取消操作：
1）可以针对某些个request做取消操作：
@Override public void onStop() { for (Request <?> req : mRequestQueue) { req.cancel(); } }
@Override protected void onStop() { // TODO Auto-generated method stub super.onStop(); mRequestQueue.cancelAll(this); }
3）可以根据RequestFilter或者Tag来终止某些请求
给请求设置标签：
如果你想取消所有的请求，在onStop方法中添加如下代码：
@Override protected void onStop() { super.onStop(); mRequestQueue.cancelAll(new RequestQueue.RequestFilter() { @Override public boolean apply(Request<?> request) { // do I have to cancel this? return true; // -> always yes } }); }
这样你就不必担心在onResponse被调用的时候用户已经销毁Activity。这种情况下会抛出NullPointerException 异。但是post请求则需要继续，即使用户已经改变了Activity。我们可以通过使用tag来做到，在构造GET请求的时候，添加一个tag给它。
// after declaring your request request.setTag("My Tag"); mRequestQueue.add(request);
如果要取消所有指定标记My Tag的请求，只需简单的添加下面的一行代码：
mRequestQueue.cancelAll("My Tag");
这样你就只会取消My Tag请求，让其它请求不受影响。注意你必须手动在销毁的Activity中处理这种情况。
@Override rotected void onStop() { // TODO Auto-generated method stub super.onStop(); mRequestQueue.cancelAll( new RequestFilter() {}); or mRequestQueue.cancelAll(new Object());
Volley源码下载：http://download.csdn.net/detail/shark0017/8404451