Introducing: Volley Library

What is Volley?

Volley is a library that makes networking for Android apps easier and most importantly, faster.

Google I/O 2013, Google 介绍了这个高大上的玩意儿。作为 Apache 的 HttpClient 解决方案的又一选择, Volley 具有如下优点:

  1. Volley 会自动对齐所有的网络请求。
  2. Volley 提供了完全透明化的磁盘和内存缓存。
  3. Volley 提供了一套强大的“取消请求”的 API,可以轻松取消请求池中的请求。
  4. Volley提供了强大的个性化功能、debug 和 跟踪工具。

然后呢,咳咳。。。嗯嗯,技术文章要严肃!据说介个呢,就是 Volley 一词灵感的由来了。话说乍一看这一个个的真的好像那啥啊有木有!!!真是羞羞~(。•ˇ‸ˇ•。)

Volley

Where to get it?

Volley 并没有像其它库一样提供现成的 jar 包给我们,而是非常可爱地提供了整个项目的源代码供我们下载,自行编译。

1.Clone Volley 的源码:

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

2.安装 Ant

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sudo apt-get install ant1.7
sudo apt-get install ant-optional

3.准备配置环境变量

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vim ~/.bashrc

4.配置 ANDROID_HOME 环境变量,提供我的配置供参考

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export JAVA_HOME=/opt/java
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
export ANDROID_HOME=/opt/adt/sdk

5.进入 Volley 目录,编译 jar 包

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cd volley
ant jar

6.从 /volley/bin 中获得新成就——volley.jar

Sample Project

在接下来的项目中,我用了三个按钮,分别用来:

  • 获得一串Json对象
  • 获取一张图片并设置到imageView
  • 获取一张图片并设置到 Volley 提供的 NetworkImageView (Recommended)

在测试前,请确保已将之前获得的 Volley.jar 放入项目的 /libsadd to buildpath。另外,项目中有网络请求,所以请确保在 AndroidManifest.xml 中请求完全的网络访问权限。

activity_main.xml

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<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/btn_json"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Get Json" />

    <TextView
        android:id="@+id/tv_json"
        android:layout_width="match_parent"
        android:hint="This request returns your Json-formatted ip address as reponse."
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/btn_imageview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Set ImageView" />

    <ImageView
        android:id="@+id/iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/btn_networkimageview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Set NetworkImageView" />

    <com.android.volley.toolbox.NetworkImageView
        android:id="@+id/iv_net"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

MainActivity.java

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public class MainActivity extends Activity {

  private Button mButtonJson;
  private Button mButtonImageView;
  private Button mButtonNetImageView;
  private TextView mTextViewJson;
  private ImageView mImageView;
  private NetworkImageView mNetworkImageView;

  private final String JSON_URL = "http://ip.jsontest.com/";
  private final String AVATAR_URL = "http://www.gravatar.com/avatar/2395dcaf9490cb28a21bf1e75af6f352?s=160";
  private static final String TAG = MainActivity.class.getSimpleName();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      findViewById();
      setJsonListener();
      setImageViewListener();
      setNetworkImageViewListener();
  }

  /**
  * This is damned easy!!!
  */
  private void setNetworkImageViewListener() {
      mButtonNetImageView.setOnClickListener(new OnClickListener() {

          @Override
          public void onClick(View v) {
              RequestQueue requestQueue = Volley
                      .newRequestQueue(getApplicationContext());
              final LruCache<String, Bitmap> lru = new LruCache<String, Bitmap>(
                      50);
              ImageCache cache = new ImageCache() {

                  @Override
                  public void putBitmap(String key, Bitmap value) {
                      // TODO Auto-generated method stub
                      lru.put(key, value);
                  }

                  @Override
                  public Bitmap getBitmap(String key) {
                      // TODO Auto-generated method stub
                      Bitmap bitmap = lru.get(key);
                      return bitmap;
                  }
              };
              ImageLoader loader = new ImageLoader(requestQueue, cache);
              mNetworkImageView.setImageUrl(AVATAR_URL, loader);
          }
      });
  }

  /**
  * The getImageListener's calling will need 3 parameters. Here are the
  * official comments in volley's source code.
  * 
  * @param imageView
  *            The imageView that the listener is associated with.
  * @param defaultImageResId
  *            Default image resource ID to use, or 0 if it doesn't exist.
  * @param errorImageResId
  *            Error image resource ID to use, or 0 if it doesn't exist.
  */
  private void setImageViewListener() {
      mButtonImageView.setOnClickListener(new OnClickListener() {

          @Override
          public void onClick(View v) {
              RequestQueue requestQueue = Volley
                      .newRequestQueue(getApplicationContext());
              final LruCache<String, Bitmap> lru = new LruCache<String, Bitmap>(
                      50); // 50 is the cache size
              ImageCache cache = new ImageCache() {

                  @Override
                  public void putBitmap(String key, Bitmap value) {
                      lru.put(key, value);
                  }

                  @Override
                  public Bitmap getBitmap(String key) {
                      Bitmap bitmap = lru.get(key);
                      return bitmap;
                  }
              };
              ImageLoader loader = new ImageLoader(requestQueue, cache);
              // Here I use "android.R.drawable.ic_delete" simply because
              // it looks like a cross which means error.
              ImageListener listener = ImageLoader.getImageListener(
                      mImageView, 0, android.R.drawable.ic_delete);
              loader.get(AVATAR_URL, listener);
          }
      });
  }

  private void setJsonListener() {
      mButtonJson.setOnClickListener(new OnClickListener() {
          @Override
          public void onClick(View arg0) {
              // Any of your requests should be added to the RequestQueue
              // instance. Use Volley's static method instead of retriving new
              // instance manually.
              RequestQueue requestQueue = Volley
                      .newRequestQueue(getApplicationContext());
              // Build up the request
              JsonObjectRequest request = new JsonObjectRequest(
                      Request.Method.GET, JSON_URL, null,
                      new Listener<JSONObject>() {

                          @Override
                          public void onResponse(JSONObject response) {
                              // TODO Auto-generated method stub
                              mTextViewJson.setText(response.toString());
                          }
                      }, new Response.ErrorListener() {

                          @Override
                          public void onErrorResponse(VolleyError arg0) {
                              // TODO Auto-generated method stub
                              Log.i(TAG, "---->onErrorResponse");
                          }
                      });
              // Add the request to the request queue
              requestQueue.add(request);
          }
      });
  }

  private void findViewById() {
      mButtonJson = (Button) findViewById(R.id.btn_json);
      mButtonImageView = (Button) findViewById(R.id.btn_imageview);
      mButtonNetImageView = (Button) findViewById(R.id.btn_networkimageview);
      mTextViewJson = (TextView) findViewById(R.id.tv_json);
      mImageView = (ImageView) findViewById(R.id.iv);
      mNetworkImageView = (NetworkImageView) findViewById(R.id.iv_net);
  }
}

References

《Google I/O 2013 – Volley: Easy, Fast Networking for Android》

《Android 网络通信框架 Volley 简介》

《快速构建Android REST客户端系列》

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