Android库Volley的使用介绍

Android Volley 是Google开发的一个网络lib，可以让你更加简单并且快速的访问网络数据。Volley库的网络请求都是异步的，你不必担心异步处理问题。

Volley的优点：

请求队列和请求优先级
请求Cache和内存管理
扩展性性强
可以取消请求

下载和编译volley.jar

需要安装git，ant，android sdk

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

编译jar：
android update project -p . ant jar

添加volley.jar到你的项目中 不过已经有人将volley的代码放到github上了：
https://github.com/mcxiaoke/android-volley，你可以使用更加简单的方式来使用volley：

Maven

format: jar

<span class="tag"><<span class="title">dependency</span>></span>
    <span class="tag"><<span class="title">groupId</span>></span>com.mcxiaoke.volley<span class="tag"></<span class="title">groupId</span>></span>
    <span class="tag"><<span class="title">artifactId</span>></span>library<span class="tag"></<span class="title">artifactId</span>></span>
    <span class="tag"><<span class="title">version</span>></span>1.0.6<span class="tag"></<span class="title">version</span>></span>
<span class="tag"></<span class="title">dependency</span>></span>

Gradle

format: jar

compile 'com.mcxiaoke.volley:library:1.0.6'

Volley工作原理图

{.fancybox}

创建Volley 单例

使用volley时，必须要创建一个请求队列RequestQueue，使用请求队列的最佳方式就是将它做成一个单例，整个app使用这么一个请求队列。

<span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">AppController</span> <span class="keyword">extends</span> <span class="title">Application</span> </span>{

<span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">final</span> String TAG = AppController.class
        .getSimpleName();

<span class="keyword">private</span> RequestQueue mRequestQueue;
<span class="keyword">private</span> ImageLoader mImageLoader;

<span class="keyword">private</span> <span class="keyword">static</span> AppController mInstance;

<span class="annotation">@Override</span>
<span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onCreate</span>() {
    <span class="keyword">super</span>.onCreate();
    mInstance = <span class="keyword">this</span>;
}

<span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">synchronized</span> AppController <span class="title">getInstance</span>() {
    <span class="keyword">return</span> mInstance;
}

<span class="keyword">public</span> RequestQueue <span class="title">getRequestQueue</span>() {
    <span class="keyword">if</span> (mRequestQueue == <span class="keyword">null</span>) {
        mRequestQueue = Volley.newRequestQueue(getApplicationContext());
    }

    <span class="keyword">return</span> mRequestQueue;
}

<span class="keyword">public</span> ImageLoader <span class="title">getImageLoader</span>() {
    getRequestQueue();
    <span class="keyword">if</span> (mImageLoader == <span class="keyword">null</span>) {
        mImageLoader = <span class="keyword">new</span> ImageLoader(<span class="keyword">this</span>.mRequestQueue,
                <span class="keyword">new</span> LruBitmapCache());
    }
    <span class="keyword">return</span> <span class="keyword">this</span>.mImageLoader;
}

<span class="keyword">public</span> <T> <span class="keyword">void</span> <span class="title">addToRequestQueue</span>(Request<T> req, String tag) {
    <span class="comment">// set the default tag if tag is empty</span>
    req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
    getRequestQueue().add(req);
}

<span class="keyword">public</span> <T> <span class="keyword">void</span> <span class="title">addToRequestQueue</span>(Request<T> req) {
    req.setTag(TAG);
    getRequestQueue().add(req);
}

<span class="keyword">public</span> <span class="keyword">void</span> <span class="title">cancelPendingRequests</span>(Object tag) {
    <span class="keyword">if</span> (mRequestQueue != <span class="keyword">null</span>) {
        mRequestQueue.cancelAll(tag);
    }
}
}

另外，你还需要一个Cache来存放请求的图片：

<span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">LruBitmapCache</span> <span class="keyword">extends</span> <span class="title">LruCache</span><<span class="title">String</span>, <span class="title">Bitmap</span>> <span class="title">implement</span> <span class="title">ImageCache</span> </span>{
    <span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">getDefaultLruCacheSize</span>() {
        <span class="keyword">final</span> <span class="keyword">int</span> maxMemory = (<span class="keyword">int</span>) (Runtime.getRuntime().maxMemory() / <span class="number">1024</span>);
        <span class="keyword">final</span> <span class="keyword">int</span> cacheSize = maxMemory / <span class="number">8</span>;

        <span class="keyword">return</span> cacheSize;
    }

    <span class="keyword">public</span> <span class="title">LruBitmapCache</span>() {
        <span class="keyword">this</span>(getDefaultLruCacheSize());
    }

    <span class="keyword">public</span> <span class="title">LruBitmapCache</span>(<span class="keyword">int</span> sizeInKiloBytes) {
        <span class="keyword">super</span>(sizeInKiloBytes);
    }

    <span class="annotation">@Override</span>
    <span class="keyword">protected</span> <span class="keyword">int</span> <span class="title">sizeOf</span>(String key, Bitmap value) {
        <span class="keyword">return</span> value.getRowBytes() * value.getHeight() / <span class="number">1024</span>;
    }

    <span class="annotation">@Override</span>
    <span class="keyword">public</span> Bitmap <span class="title">getBitmap</span>(String url) {
        <span class="keyword">return</span> get(url);
    }

    <span class="annotation">@Override</span>
    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">putBitmap</span>(String url, Bitmap bitmap) {
        put(url, bitmap);
    }
}

别忘记在AndroidManifest.xml文件中添加android.permission.INTERNET权限。

创建Json请求

volley自带了JsonObjectRequest和JsonArrayRequest分别来处理Json对象请求和Json数据请求（但是voley没有使用gson库写一个GsonRequest，发送一个request，volley直接返回一个java对象，不过我们可以自己写）。

创建json object请求

发送一个请求只要这么简单，创建一个JsonRequest对象，写好response回调接口，并把这个请求放到请求队列中就可以了。JsonArrayRequest也类似。

<span class="comment">// Tag used to cancel the request</span>
String tag_json_obj = <span class="string">"json_obj_req"</span>;
String url = <span class="string">"http://api.androidhive.info/volley/person_object.json"</span>;

JsonObjectRequest jsonObjReq = <span class="keyword">new</span> JsonObjectRequest(Method.GET,url, <span class="keyword">null</span>,
            <span class="keyword">new</span> Response.Listener<JSONObject>() {

                <span class="annotation">@Override</span>
                <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onResponse</span>(JSONObject response) {
                    Log.d(TAG, response.toString());
                }
            }, <span class="keyword">new</span> Response.ErrorListener() {

                <span class="annotation">@Override</span>
                <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onErrorResponse</span>(VolleyError error) {
                    VolleyLog.d(TAG, <span class="string">"Error: "</span> + error.getMessage());
                }
            });

<span class="comment">// Adding request to request queue</span>
AppController.getInstance().addToRequestQueue(jsonObjReq, tag_json_obj);

创建String请求

StringRequest可以用来请求任何string类型的数据：json，xml，文本等等。

<span class="comment">// Tag used to cancel the request</span>
String  tag_string_req = <span class="string">"string_req"</span>;

String url = <span class="string">"http://api.androidhive.info/volley/string_response.html"</span>;

ProgressDialog pDialog = <span class="keyword">new</span> ProgressDialog(<span class="keyword">this</span>);
pDialog.setMessage(<span class="string">"Loading..."</span>);
pDialog.show();     

StringRequest strReq = <span class="keyword">new</span> StringRequest(Method.GET,
            url, <span class="keyword">new</span> Response.Listener<String>() {

                <span class="annotation">@Override</span>
                <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onResponse</span>(String response) {
                    Log.d(TAG, response.toString());
                    pDialog.hide();

                }
            }, <span class="keyword">new</span> Response.ErrorListener() {

                <span class="annotation">@Override</span>
                <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onErrorResponse</span>(VolleyError error) {
                    VolleyLog.d(TAG, <span class="string">"Error: "</span> + error.getMessage());
                    pDialog.hide();
                }
            });

<span class="comment">// Adding request to request queue</span>
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);

创建POST请求

上面说的都是GET请求，下面来说一下POST请求，与GET请求不同的是，只要在创建请求的时候将请求类型改为POST请求，并且override Request的getParams方法即可。

<span class="comment">// Tag used to cancel the request</span>
<span class="built_in">String</span> tag_json_obj <span class="subst">=</span> <span class="string">"json_obj_req"</span>;

<span class="built_in">String</span> url <span class="subst">=</span> <span class="string">"http://api.androidhive.info/volley/person_object.json"</span>;
ProgressDialog pDialog <span class="subst">=</span> <span class="literal">new</span> ProgressDialog(this);
pDialog<span class="built_in">.</span>setMessage(<span class="string">"Loading..."</span>);
pDialog<span class="built_in">.</span>show();     

    JsonObjectRequest jsonObjReq <span class="subst">=</span> <span class="literal">new</span> JsonObjectRequest(Method<span class="built_in">.</span>POST,
            url, <span class="built_in">null</span>,
            <span class="literal">new</span> Response<span class="built_in">.</span>Listener<span class="subst"><</span>JSONObject<span class="subst">></span>() {

                @Override
                <span class="keyword">public</span> <span class="literal">void</span> onResponse(JSONObject response) {
                    <span class="keyword">Log</span><span class="built_in">.</span>d(<span class="built_in">TAG</span>, response<span class="built_in">.</span>toString());
                    pDialog<span class="built_in">.</span>hide();
                }
            }, <span class="literal">new</span> Response<span class="built_in">.</span>ErrorListener() {

                @Override
                <span class="keyword">public</span> <span class="literal">void</span> onErrorResponse(VolleyError error) {
                    VolleyLog<span class="built_in">.</span>d(<span class="built_in">TAG</span>, <span class="string">"Error: "</span> <span class="subst">+</span> error<span class="built_in">.</span>getMessage());
                    pDialog<span class="built_in">.</span>hide();
                }
            }) {

        @Override
        <span class="keyword">protected</span> <span class="built_in">Map</span><span class="subst"><</span><span class="built_in">String</span>, <span class="built_in">String</span><span class="subst">></span> getParams() {
            <span class="built_in">Map</span><span class="subst"><</span><span class="built_in">String</span>, <span class="built_in">String</span><span class="subst">></span> <span class="keyword">params</span> <span class="subst">=</span> <span class="literal">new</span> HashMap<span class="subst"><</span><span class="built_in">String</span>, <span class="built_in">String</span><span class="subst">></span>();
            <span class="keyword">params</span><span class="built_in">.</span>put(<span class="string">"name"</span>, <span class="string">"Androidhive"</span>);
            <span class="keyword">params</span><span class="built_in">.</span>put(<span class="string">"email"</span>, <span class="string">"abc@androidhive.info"</span>);
            <span class="keyword">params</span><span class="built_in">.</span>put(<span class="string">"password"</span>, <span class="string">"password123"</span>);

            <span class="keyword">return</span> <span class="keyword">params</span>;
        }

    };

<span class="comment">// Adding request to request queue</span>
AppController<span class="built_in">.</span>getInstance()<span class="built_in">.</span>addToRequestQueue(jsonObjReq, tag_json_obj);

添加请求头部信息

<span class="comment">// Tag used to cancel the request</span>
String tag_json_obj = <span class="string">"json_obj_req"</span>;

String url = <span class="string">"http://api.androidhive.info/volley/person_object.json"</span>;

ProgressDialog pDialog = <span class="keyword">new</span> ProgressDialog(<span class="keyword">this</span>);
pDialog.setMessage(<span class="string">"Loading..."</span>);
pDialog.show();     

JsonObjectRequest jsonObjReq = <span class="keyword">new</span> JsonObjectRequest(Method.POST,url, <span class="keyword">null</span>,<span class="keyword">new</span> Response.Listener<JSONObject>() {
    <span class="annotation">@Override</span>
    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onResponse</span>(JSONObject response) {
        Log.d(TAG, response.toString());
        pDialog.hide();
    }
}, <span class="keyword">new</span> Response.ErrorListener() {
    <span class="annotation">@Override</span>
    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onErrorResponse</span>(VolleyError error) {
        VolleyLog.d(TAG, <span class="string">"Error: "</span> + error.getMessage());
        pDialog.hide();
    }
}) {

<span class="javadoc">/**
* Passing some request headers
* */</span>
<span class="annotation">@Override</span>
<span class="keyword">public</span> Map<String, String> <span class="title">getHeaders</span>() <span class="keyword">throws</span> AuthFailureError {
    HashMap<String, String> headers = <span class="keyword">new</span> HashMap<String, String>();
    headers.put(<span class="string">"Content-Type"</span>, <span class="string">"application/json"</span>);
    headers.put(<span class="string">"apiKey"</span>, <span class="string">"xxxxxxxxxxxxxxx"</span>);
    <span class="keyword">return</span> headers;
}
};
<span class="comment">// Adding request to request queue</span>
AppController.getInstance().addToRequestQueue(jsonObjReq, tag_json_obj);

创建Image请求

Volley库中自带了NetworkImageView类，这个ImageView可以自动使用volley下载图片

用`NetworkImageView`加载图片

首先，说明一下，加载图片的原理：

NetworkImageView加载图片需要一个ImageLoader和一个图片URL，这个ImageLoader对象需要一个请求队列对象和ImageCahe对象。调用NetworkImageView的setUrl方法后，首先会判断当前ImageView的URL和新传入的URL是否一致，如果相同，就不用再发送http请求了，如果不同，那么就使用ImageLoader对象来发送http请求获取图片。

<span class="constant">ImageLoader imageLoader</span> = AppController.getInstance().getImageLoader();
<span class="comment">// If you are using NetworkImageView</span>
imgNetWorkView.setImageUrl(Const.URL_IMAGE, imageLoader);

加载一个图片只要这么简单~~~

用ImageView来加载图片

这个过程和NetworkImageView类似

ImageLoader imageLoader = AppController.getInstance().getImageLoader();

<span class="comment">// If you are using normal ImageView</span>
imageLoader.get(Const.URL_IMAGE, <span class="keyword">new</span> ImageListener() {

    <span class="annotation">@Override</span>
    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onErrorResponse</span>(VolleyError error) {
        Log.e(TAG, <span class="string">"Image Load Error: "</span> + error.getMessage());
    }

    <span class="annotation">@Override</span>
    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onResponse</span>(ImageContainer response, <span class="keyword">boolean</span> arg1) {
        <span class="keyword">if</span> (response.getBitmap() != <span class="keyword">null</span>) {
            <span class="comment">// load image into imageview</span>
            imageView.setImageBitmap(response.getBitmap());
        }
    }
});

可以再简单一点：

// Loading image with placeholder <span class="literal">and</span> <span class="built_in">error</span> image
imageLoader.get(<span class="keyword">Const</span>.URL_IMAGE, ImageLoader.getImageListener(imageView, R.drawable.ico_loading, R.drawable.ico_error));

ImageLoader.getImageListener方法中已经写了一个默认的ImageListener了

Volley Cache

volley中自带了强大的cache机制来管理请求cache，这会减少网络请求次数和用户等待时间。

从请求Cache中加载请求

<span class="keyword">Cache</span> <span class="keyword">cache</span> <span class="subst">=</span> AppController<span class="built_in">.</span>getInstance()<span class="built_in">.</span>getRequestQueue()<span class="built_in">.</span>getCache();
Entry entry <span class="subst">=</span> <span class="keyword">cache</span><span class="built_in">.</span>get(url);
<span class="keyword">if</span>(entry <span class="subst">!=</span> <span class="built_in">null</span>){
    try {
        <span class="built_in">String</span> <span class="built_in">data</span> <span class="subst">=</span> <span class="literal">new</span> <span class="built_in">String</span>(entry<span class="built_in">.</span><span class="built_in">data</span>, <span class="string">"UTF-8"</span>);
        <span class="comment">// handle data, like converting it to xml, json, bitmap etc.,</span>
    } catch (UnsupportedEncodingException e) {      
        e<span class="built_in">.</span>printStackTrace();
        }
    }
}<span class="keyword">else</span>{
    <span class="comment">// Cached response doesn't exists. Make network call here</span>
}

使请求缓存失效

失效并不意味这删除，Volley还会继续使用缓存的对象直到从服务器上获取到了新的数据，新的数据会覆盖旧的数据。

AppController.getInstance().getRequestQueue().getCache().invalidate(url, <span class="literal">true</span>);

关闭Cache

如果你想将某一个请求的Cache功能关闭，直接调用Request的setShouldCache()方法就可以：

<span class="comment">// String request</span>
StringRequest stringReq <span class="subst">=</span> <span class="literal">new</span> StringRequest(<span class="attribute">...</span><span class="built_in">.</span>);

<span class="comment">// disable cache</span>
stringReq<span class="built_in">.</span>setShouldCache(<span class="literal">false</span>);

将某一URL的Cache删除

调用Cache的remove方法可以删除这个URL的cache:

AppController.getInstance().getRequestQueue().getCache().<span class="built_in">remove</span>(url);

删除所有的Cache

AppController.getInstance().getRequestQueue().getCache().<span class="keyword">clear</span>();

取消请求

在你添加一个请求到请求队列中的时候，你可以发现，addToRequestQueue(request, tag)方法还接受一个tag参数，这个tag就是用来标记某一类请求的，这样就可以取消这个tag的所有请求了：

<span class="built_in">String</span> tag_json_arry = <span class="string">"json_req"</span>;
ApplicationController.getInstance().getRequestQueue().cancelAll(<span class="string">"feed_request"</span>);

请求优先级

在创建一个request的时候可以Override Request方法的getPriority方法返回一个优先级，优先级分为：Normal, Low, Immediate, High

<span class="keyword">private</span> Priority priority = Priority.HIGH;

StringRequest strReq = <span class="keyword">new</span> StringRequest(Method.GET,
            Const.URL_STRING_REQ, <span class="keyword">new</span> Response.Listener<String>() {

                <span class="annotation">@Override</span>
                <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onResponse</span>(String response) {
                    Log.d(TAG, response.toString());
                    msgResponse.setText(response.toString());
                    hideProgressDialog();

                }
            }, <span class="keyword">new</span> Response.ErrorListener() {

                <span class="annotation">@Override</span>
                <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onErrorResponse</span>(VolleyError error) {
                    VolleyLog.d(TAG, <span class="string">"Error: "</span> + error.getMessage());
                    hideProgressDialog();
                }
            }) {
        <span class="annotation">@Override</span>
        <span class="keyword">public</span> Priority <span class="title">getPriority</span>() {
            <span class="keyword">return</span> priority;
        }

    };

Missing! 创建xml请求 {#Missing!_创建xml请求}

就像创建Gson请求一样，你可以自定义一个XMLRequest类来请求xml数据

下载和编译volley.jar#

Maven#

Gradle#

Volley工作原理图#

创建Volley 单例#

创建Json请求#

创建json object请求#

创建String请求#

创建POST请求#

添加请求头部信息#

创建Image请求#

用NetworkImageView加载图片#

用ImageView来加载图片#

Volley Cache#

从请求Cache中加载请求#

使请求缓存失效#

关闭Cache#

将某一URL的Cache删除#

删除所有的Cache#

取消请求#

请求优先级#

Missing! 创建xml请求 {#Missing!_创建xml请求}#

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