Google Volley使用之基础

开源项目链接

Volley 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

啥是Google Android Volley？

一句简单的回答：Volley就是集AsyncHttpClient和Universal-Image-Loader优点于一身的一个Google亲儿子开源框架。

Google在I/O 2013大会上发布了Volley。它是Android平台上的网络通信库，能使网络通信更快，更简单，更健壮。其最明显的一个优点就是特别适合数据量不大但是通信频繁的场景，最明显的缺点就是大数据传输表现的很糟糕。

Volley提供了如下的便利功能：

JSON数据和图像等的异步下载；网络请求排序（scheduling）；网络请求优先级处理；缓存；多级别取消请求；与Activity生命周期联动（Activity结束时同时取消所有网络请求）；

Volley对APP的版本要求是android:minSdkVersion为8。

使用newRequestQueue和StringRequest

Volley的用法非常简单，这里使用官方例子发起一条HTTP GET请求，然后接收HTTP响应。首先需要获取到一个RequestQueue对象，可以调用如下方法获取到：

<code class="language-android hljs fix has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-attribute" style="box-sizing: border-box;">RequestQueue mQueue </span>=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;"> Volley.newRequestQueue(context);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

这里拿到的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，基本上在每一个需要和网络交互的Activity中创建一个RequestQueue对象就足够了。

StringRequest的构造函数需要传入四个参数（有一个三个参数的构造函数，默认是GET方式），第一个参数就是目标服务器的URL地址，第二个参数是服务器响应成功的回调，第三个参数是服务器响应失败的回调。将这个StringRequest对象添加到RequestQueue里面就可以了。使用Volley时您可以从任何线程开始请求，但响应始终传递到了主线程上。

<code class="language-android hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> TextView mTextView = (TextView) findViewById(R.id.text);
...

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Instantiate the RequestQueue.</span>
RequestQueue queue = Volley.newRequestQueue(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
String url =<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.google.com"</span>;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Request a string response from the provided URL.</span>
StringRequest stringRequest = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> StringRequest(Request.Method.GET, url,
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Response.Listener<String>() {
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onResponse</span>(String response) {
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Display the first 500 characters of the response string.</span>
        mTextView.setText(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response is: "</span>+ response.substring(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span>));
    }
}, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Response.ErrorListener() {
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onErrorResponse</span>(VolleyError error) {
        mTextView.setText(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"That didn't work!"</span>);
    }
});
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Add the request to the RequestQueue.</span>
queue.add(stringRequest);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>

如上代码就示范了一个简单的HTTP GET请求。

既然HTTP GET的例子这么easy搞定，是不是该再整一个POST的例子呢？

POST有点曲线救国，因为StringRequest中并没有提供设置POST参数的方法，但是当发出POST请求的时候，Volley会尝试调用StringRequest父类Request的getParams()方法来获取POST参数，所以我们只需要重写StringRequest的getParams()方法，在这里设置POST参数就可以了，代码如下所示：

<code class="language-android hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">RequestQueue <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">queue</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> Volley<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>newRequestQueue(this);

StringRequest stringRequest <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> StringRequest(Method<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>POST, url,  listener, errorListener) {  
    @Override 
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Map</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span>, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> getParams() throws AuthFailureError {  
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Map</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span>, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">map</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> HashMap<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span>, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>();  
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">map</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>put(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"key1"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"value1"</span>);  
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">map</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>put(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"key2"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"value2"</span>);  
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">map</span>;  
    }  
}; 

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">queue</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>add(stringRequest);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

如上代码就示范了一个简单的HTTP POST请求。

使用newRequestQueue和JsonRequest

和StringRequest基本上差不多，JsonRequest也是继承自Request类的，不过JsonRequest是一个抽象类，我们无法直接创建它的实例。JsonRequest有两个直接的子类，JsonObjectRequest和JsonArrayRequest。所以对于JSON格式的数据基本没啥压力了，他都帮你搞完了，如下展示一个简单例子：

<code class="language-android hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">RequestQueue queue = Volley.newRequestQueue(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);

JsonObjectRequest jsonObjectRequest = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> JsonObjectRequest(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://json_test.php"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>,  
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Response.Listener<JSONObject>() {  
            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onResponse</span>(JSONObject response) {  
                Log.d(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"TAG"</span>, response.toString());  
            }  
        }, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Response.ErrorListener() {  
            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onErrorResponse</span>(VolleyError error) {  
                Log.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"TAG"</span>, error.getMessage(), error);  
            }  
        });  

queue.add(stringRequest);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

如上就是一个Volley的JSON HTTP的简单例子咯！

取消Request

要取消一个请求，调用cancel()即可。一旦取消，Volley保证你的响应处理程序将永远不会被调用。这意味着在实践中，你可以取消所有待定的请求在你Activity的onStop()方法中，你不必乱抛垃圾的响应处理程序或者检查getActivity() == NULL，无论onSaveInstanceState()是否已经被调用。

你发出去的请求必须要自己保证是可控的，在这里还有一个更简单的方法：你可以标记发送的每个请求对象，然后你可以使用这个标签来提供请求取消的范围。

这里是一个使用字符串值标签的例子：

<code class="language-android hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TAG = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyTag"</span>;
StringRequest stringRequest; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Assume this exists.</span>
RequestQueue mRequestQueue;  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Assume this exists.</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Set the tag on the request.</span>
stringRequest.setTag(TAG);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Add the request to the RequestQueue.</span>
mRequestQueue.add(stringRequest);

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onStop</span> () {
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onStop();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mRequestQueue != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
        mRequestQueue.cancelAll(TAG);
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

现在是不是发现Volley灰常简单了呢！就是举一反三的操作。

好了，不扯了，网络HTTP的Volley简单使用先说到这里。

使用newRequestQueue和ImageRequest

ImageRequest也是继承自Request的，因此它的用法和上面的也是基本相同的。

<code class="language-android hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">ImageRequest imageRequest = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ImageRequest(  
        <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://developer.android.com/images/home/aw_dac.png"</span>,  
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Response.Listener<Bitmap>() {  
            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onResponse</span>(Bitmap response) {  
                imageView.setImageBitmap(response);  
            }  
        }, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, Config.RGB_565, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Response.ErrorListener() {  
            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onErrorResponse</span>(VolleyError error) {  
                imageView.setImageResource(R.drawable.default_image);  
            }  
        });  </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

ImageRequest的构造函数有六个参数，第一个参数是图片URL；第二个参数是图片请求成功的回调；第三第四个参数分别用于指定允许图片最大的宽度和高度，如果指定的网络图片的宽度或高度大于这里的最大值，则会对图片进行压缩，指定成0的话就表示不管图片有多大，都不会进行压缩；第五个参数用于指定图片深度；第六个参数是图片请求失败的回调。

使用newRequestQueue和ImageLoader

ImageLoader也可以用于加载网络上的图片，并且它的内部也是使用ImageRequest来实现的，不过ImageLoader明显要比ImageRequest更加高效，因为它不仅可以帮我们对图片进行缓存，还可以过滤掉重复的链接，避免重复发送请求。

由于ImageLoader已经不是继承自Request，所以它的用法变为如下：

创建一个RequestQueue对象。创建一个ImageLoader对象。获取一个ImageListener对象。调用ImageLoader的get()方法加载网络上的图片。

<code class="language-android hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">RequestQueue mQueue = Volley.newRequestQueue(context);

ImageLoader imageLoader = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ImageLoader(mQueue, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ImageCache() {  
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">putBitmap</span>(String url, Bitmap bitmap) {  
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//未实现</span>
    }  

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Bitmap <span class="hljs-title" style="box-sizing: border-box;">getBitmap</span>(String url) {  
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//未实现</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;  
    }  
});

ImageListener listener = ImageLoader.getImageListener(imageView,  
        R.drawable.default_image, R.drawable.failed_image);

imageLoader.get(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://google/pictures/1201.jpeg"</span>, listener, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span>);        </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

如上简单使用了ImageLoader进行图片加载。

现在进行升级，实现ImageCache接口如下：

<code class="language-android hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">BitmapCache</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ImageCache</span> {</span>  

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> LruCache<String, Bitmap> mCache;  

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">BitmapCache</span>() {  
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> maxSize = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1024</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1024</span>;  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//演示写死，实际需要动态计算</span>
        mCache = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> LruCache<String, Bitmap>(maxSize) {  
            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">sizeOf</span>(String key, Bitmap bitmap) {  
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> bitmap.getRowBytes() * bitmap.getHeight();  
            }  
        };  
    }  

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Bitmap <span class="hljs-title" style="box-sizing: border-box;">getBitmap</span>(String url) {  
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mCache.get(url);  
    }  

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> 
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">putBitmap</span>(String url, Bitmap bitmap) {  
        mCache.put(url, bitmap);  
    }  
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

这里这么搞一下就简单的把ImageLoader优势展示了一把。

使用newRequestQueue和NetworkImageView

NetworkImageView是一个继承自ImageView的View控件，拥有ImageView控件的所有功能，并且在ImageView的基础上加入了加载网络图片的功能。NetworkImageView控件的用法分为以下五步：

创建一个RequestQueue对象。创建一个ImageLoader对象。在布局文件中添加一个NetworkImageView控件。在代码中获取该控件的实例。设置要加载的图片地址。

这里以XML文件结合java的方式演示：

<code class="language-android hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><LinearLayout xmlns:android=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://schemas.android.com/apk/res/android"</span> 
    android:layout_width=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fill_parent"</span> 
    android:layout_height=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fill_parent"</span> 
    android:orientation=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"vertical"</span> > 

    <<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.android</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.volley</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toolbox</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.NetworkImageView</span>   
        android:id=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"@+id/network_image_view"</span> 
        android:layout_width=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"200dp"</span> 
        android:layout_height=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"200dp"</span> 
        android:layout_gravity=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"center_horizontal"</span> /> 

</LinearLayout></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>

<code class="language-android hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">networkImageView = (NetworkImageView) findViewById(R<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.id</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.network</span>_image_view)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

networkImageView<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDefaultImageResId</span>(R<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.drawable</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.default</span>_image)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  </span>
networkImageView<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setErrorImageResId</span>(R<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.drawable</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.failed</span>_image)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  </span>
networkImageView<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setImageUrl</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://img.my.csdn.net/uploads/201404/13/1397393290_5765.jpeg"</span>, imageLoader)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

如上演示了Volley的一些基本使用特性和方法。

Volley请求管理方式

在Android Developer上看到的这幅图：

RequestQueue会维护一个缓存调度线程（cache线程）和一个网络调度线程池（net线程），当一个Request被加到队列中的时候，cache线程会把这个请求进行筛选：如果这个请求的内容可以在缓存中找到，cache线程会亲自解析相应内容，并分发到主线程（UI）。如果缓存中没有，这个request就会被加入到另一个NetworkQueue，所有真正准备进行网络通信的request都在这里，第一个可用的net线程会从NetworkQueue中拿出一个request扔向服务器。当响应数据到的时候，这个net线程会解析原始响应数据，写入缓存，并把解析后的结果返回给主线程。

【工匠若水 http://blog.csdn.net/yanbober】 继续阅读《Google Volley使用之自定义》 http://blog.csdn.net/yanbober/article/details/45307099