Android中通过Messenger与Service实现进程间双向通信

转载博客原文：http://blog.csdn.net/iispring/article/details/48329925

Android中的Service和其调用者既可以在同一个App中，也可以在不同的App。如果Service在App1中，而调用Service的客户端在App2中，那么我们就可以用Service实现进程间的相互通信。本文将介绍如何通过bindService和Messenger实现进程间通信（IPC），如果对bindService绑定服务和Binder不熟悉，可参见《Android中bindService的使用及Service生命周期》，理解该博文是本文的基础。

让Service实现与其他进程通信的关键是Messenger，以及与其相关的IBinder和Hanlder。如果对Handler不熟悉，可参见《Android中Handler的使用》。

Messenger使用步骤

以下是如何使用Messenger的步骤: 

1. Service需要实现一个Hanlder，用以处理从客户端收到的消息 

2. 用该Handler创建一个Messenger对象，Messenger对象内部会引用该Handler对象 

3. 用创建好的Messenger对象获得一个IBinder实例，并且将该IBinder通过Service的onBind方法返回给各个客户端 

4. 客户端通过收到的IBinder对象实例化一个Messenger对象，该Messenger内部指向指向Service中的Handler。客户端通过该Messenger对象就可以向Service中的Hanlder发送消息。 

5. Service中的Hanlder收到消息后，在Handler中的handleMessage方法中处理消息。 

6. 通过上面的第4步与第5步，就完成了客户端向Service发送消息并且Service接收到消息的单向通信过程，即客户端 -> Service。如果要实现Service向客户端回消息的通信过程，即Service -> 客户端，那么前提是在客户端中也需要像Service一样内部维护有一个指向Handler的Messenger。当在第四步中客户端向Service发送信息时，将Message的replyTo属性设置为客户端自己的Messenger。这样在第5步Service在Handler的handleMessage中处理收到的消息时，可以通过Message的Messenger再向客户端发送Message，这样客户端内维护的Handler对象就会收到来自于Service的Message，从而完成Service向客户端发送消息且客户端接收到消息的通信过程。

综上六步就能完成客户端与Service的跨进程双向通信过程: 

客户端 -> Service -> 客户端

为了演示客户端与Service的跨进程通信，我建立了两个应用ClientApp和ServiceApp，两个应用的名称也是见名知意: 

1. ClientApp, 该App是客户端，用于调用服务 

2. ServiceApp，该App是Service端，用于供客户端ClientApp调用

Service代码

ServiceApp中只有一个MyService类，没有其他Activity，也就是说ServiceApp没有任何UI界面。ServiceApp的manifest.xml文件如下所示:

<code class="hljs xml 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-pi" style="color: rgb(0, 102, 102); box-sizing: border-box;"><?xml version="1.0" encoding="utf-8"?></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">manifest</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">xmlns:android</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"http://schemas.android.com/apk/res/android"</span>
<span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">package</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"com.ispring2.serviceapp"</span> ></span>

<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">application
</span>        <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:allowBackup</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>
<span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:icon</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"@drawable/ic_launcher"</span>
<span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:label</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"ServiceApp"</span>></span>

<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">service
</span>            <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".MyService"</span>
<span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:enabled</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>
<span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:exported</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span> ></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"com.ispring2.action.MYSERVICE"</span> /></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.DEFAULT"</span> /></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">service</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">application</span>></span>

<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">manifest</span>></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><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul><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></ul>

我们在ServiceApp的manifest.xml文件中注册了MyService，并通过exported=”true”将其声明为可被其他App调用的。需要注意的是，我们将其action设置为自定义的action（com.ispring2.action.MYSERVICE），这是为了方便客户端通过其action启动MyService。并且我们将其设置了值为android.intent.category.DEFAULT的category。

ServiceApp中MyService的代码如下所示:

<code class="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;">package</span> com.ispring2.serviceapp;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.app.Service;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.Intent;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Bundle;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Handler;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.IBinder;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Message;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Messenger;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.RemoteException;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.util.Log;

<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);">MyService</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Service</span> {</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</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> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> RECEIVE_MESSAGE_CODE = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0001</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</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> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> SEND_MESSAGE_CODE = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0002</span>;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//clientMessenger表示的是客户端的Messenger，可以通过来自于客户端的Message的replyTo属性获得，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//其内部指向了客户端的ClientHandler实例，可以用clientMessenger向客户端发送消息</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Messenger clientMessenger = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//serviceMessenger是Service自身的Messenger，其内部指向了ServiceHandler的实例</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//客户端可以通过IBinder构建Service端的Messenger，从而向Service发送消息，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//并由ServiceHandler接收并处理来自于客户端的消息</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Messenger serviceMessenger = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Messenger(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ServiceHandler());

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//MyService用ServiceHandler接收并处理来自于客户端的消息</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</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);">ServiceHandler</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Handler</span> {</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> <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;">handleMessage</span>(Message msg) {
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ServiceHandler -> handleMessage"</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(msg.what == RECEIVE_MESSAGE_CODE){
Bundle data = msg.getData();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(data != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>){
String str = data.getString(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>);
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyService收到客户端如下信息: "</span> + str);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//通过Message的replyTo获取到客户端自身的Messenger，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Service可以通过它向客户端发送消息</span>
clientMessenger = msg.replyTo;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(clientMessenger != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>){
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyService向客户端回信"</span>);
Message msgToClient = Message.obtain();
msgToClient.what = SEND_MESSAGE_CODE;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//可以通过Bundle发送跨进程的信息</span>
Bundle bundle = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Bundle();
bundle.putString(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"你好，客户端，我是MyService"</span>);
msgToClient.setData(bundle);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span>{
clientMessenger.send(msgToClient);
}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (RemoteException e){
e.printStackTrace();
Log.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyService向客户端发送信息失败: "</span> + e.getMessage());
}
}
}
}
}

<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;">onCreate</span>() {
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyService -> onCreate"</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate();
}

<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> IBinder <span class="hljs-title" style="box-sizing: border-box;">onBind</span>(Intent intent) {
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyServivce -> onBind"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//获取Service自身Messenger所对应的IBinder，并将其发送共享给所有客户端</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> serviceMessenger.getBinder();
}

<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;">onDestroy</span>() {
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"MyService -> onDestroy"</span>);
clientMessenger = <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;">super</span>.onDestroy();
}
}</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><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li></ul><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><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li></ul>

MyService中有一个内部类ServiceHandler，继承自Hanlder并重写了handleMessage方法，MyService用ServiceHandler接收并处理来自于客户端的消息。
MyService中，我们用ServiceHandler的实例初始化了serviceMessenger。serviceMessenger是Service自身的Messenger，其内部指向了ServiceHandler的实例，客户端可以通过IBinder构建Service端的Messenger，从而向Service发送消息，并由ServiceHandler接收并处理来自于客户端的消息。

客户端代码

客户端应用ClientApp就一个MainActivity，其界面上就只有两个按钮:bindService和unbindService, 界面如下: 



代码如下所示：

<code class="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;">package</span> com.ispring.clientapp;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.app.Activity;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.ComponentName;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.Intent;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.ServiceConnection;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.pm.PackageManager;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.pm.ResolveInfo;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Bundle;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Handler;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.IBinder;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Message;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.Messenger;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.os.RemoteException;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.util.Log;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.view.View;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.widget.Button;

<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);">MainActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Activity</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);">Button</span>.<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">OnClickListener</span> {</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</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> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> SEND_MESSAGE_CODE = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0001</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</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> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> RECEIVE_MESSAGE_CODE = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0002</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> isBound = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//用于启动MyService的Intent对应的action</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String SERVICE_ACTION = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"com.ispring2.action.MYSERVICE"</span>;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//serviceMessenger表示的是Service端的Messenger，其内部指向了MyService的ServiceHandler实例</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//可以用serviceMessenger向MyService发送消息</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Messenger serviceMessenger = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//clientMessenger是客户端自身的Messenger，内部指向了ClientHandler的实例</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//MyService可以通过Message的replyTo得到clientMessenger，从而MyService可以向客户端发送消息，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//并由ClientHandler接收并处理来自于Service的消息</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Messenger clientMessenger = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Messenger(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ClientHandler());

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//客户端用ClientHandler接收并处理来自于Service的消息</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</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);">ClientHandler</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Handler</span> {</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> <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;">handleMessage</span>(Message msg) {
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ClientHandler -> handleMessage"</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(msg.what == RECEIVE_MESSAGE_CODE){
Bundle data = msg.getData();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(data != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>){
String str = data.getString(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>);
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端收到Service的消息: "</span> + str);
}
}
}
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> ServiceConnection conn = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ServiceConnection() {
<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;">onServiceConnected</span>(ComponentName name, IBinder binder) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//客户端与Service建立连接</span>
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端 onServiceConnected"</span>);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//我们可以通过从Service的onBind方法中返回的IBinder初始化一个指向Service端的Messenger</span>
serviceMessenger = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Messenger(binder);
isBound = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;

Message msg = Message.obtain();
msg.what = SEND_MESSAGE_CODE;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//此处跨进程Message通信不能将msg.obj设置为non-Parcelable的对象，应该使用Bundle</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//msg.obj = "你好，MyService，我是客户端";</span>
Bundle data = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Bundle();
data.putString(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"你好，MyService，我是客户端"</span>);
msg.setData(data);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//需要将Message的replyTo设置为客户端的clientMessenger，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//以便Service可以通过它向客户端发送消息</span>
msg.replyTo = clientMessenger;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端向service发送信息"</span>);
serviceMessenger.send(msg);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (RemoteException e) {
e.printStackTrace();
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端向service发送消息失败: "</span> + e.getMessage());
}
}

<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;">onServiceDisconnected</span>(ComponentName name) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//客户端与Service失去连接</span>
serviceMessenger = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
isBound = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端 onServiceDisconnected"</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;">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;">onCreate</span>(Bundle savedInstanceState) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}

<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;">onClick</span>(View v) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(v.getId() == R.id.btnBindService){
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//单击了bindService按钮</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(!isBound){
Intent intent = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Intent();
intent.setAction(SERVICE_ACTION);
intent.addCategory(Intent.CATEGORY_DEFAULT);

PackageManager pm = getPackageManager();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//我们先通过一个隐式的Intent获取可能会被启动的Service的信息</span>
ResolveInfo info = pm.resolveService(intent, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(info != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>){
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果ResolveInfo不为空，说明我们能通过上面隐式的Intent找到对应的Service</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//我们可以获取将要启动的Service的package信息以及类型</span>
String packageName = info.serviceInfo.packageName;
String serviceNmae = info.serviceInfo.name;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//然后我们需要将根据得到的Service的包名和类名，构建一个ComponentName</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//从而设置intent要启动的具体的组件信息，这样intent就从隐式变成了一个显式的intent</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//之所以大费周折将其从隐式转换为显式intent，是因为从Android 5.0 Lollipop开始，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Android不再支持通过通过隐式的intent启动Service，只能通过显式intent的方式启动Service</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在Android 5.0 Lollipop之前的版本倒是可以通过隐式intent启动Service</span>
ComponentName componentName = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ComponentName(packageName, serviceNmae);
intent.setComponent(componentName);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span>{
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端调用bindService方法"</span>);
bindService(intent, conn, BIND_AUTO_CREATE);
}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span>(Exception e){
e.printStackTrace();
Log.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, e.getMessage());
}
}
}
}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(v.getId() == R.id.btnUnbindService){
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//单击了unbindService按钮</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(isBound){
Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DemoLog"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"客户端调用unbindService方法"</span>);
unbindService(conn);
}
}
}
}</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><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li><li style="box-sizing: border-box; padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li><li style="box-sizing: border-box; padding: 0px 5px;">98</li><li style="box-sizing: border-box; padding: 0px 5px;">99</li><li style="box-sizing: border-box; padding: 0px 5px;">100</li><li style="box-sizing: border-box; padding: 0px 5px;">101</li><li style="box-sizing: border-box; padding: 0px 5px;">102</li><li style="box-sizing: border-box; padding: 0px 5px;">103</li><li style="box-sizing: border-box; padding: 0px 5px;">104</li><li style="box-sizing: border-box; padding: 0px 5px;">105</li><li style="box-sizing: border-box; padding: 0px 5px;">106</li><li style="box-sizing: border-box; padding: 0px 5px;">107</li><li style="box-sizing: border-box; padding: 0px 5px;">108</li><li style="box-sizing: border-box; padding: 0px 5px;">109</li><li style="box-sizing: border-box; padding: 0px 5px;">110</li><li style="box-sizing: border-box; padding: 0px 5px;">111</li><li style="box-sizing: border-box; padding: 0px 5px;">112</li><li style="box-sizing: border-box; padding: 0px 5px;">113</li><li style="box-sizing: border-box; padding: 0px 5px;">114</li><li style="box-sizing: border-box; padding: 0px 5px;">115</li><li style="box-sizing: border-box; padding: 0px 5px;">116</li><li style="box-sizing: border-box; padding: 0px 5px;">117</li><li style="box-sizing: border-box; padding: 0px 5px;">118</li><li style="box-sizing: border-box; padding: 0px 5px;">119</li><li style="box-sizing: border-box; padding: 0px 5px;">120</li><li style="box-sizing: border-box; padding: 0px 5px;">121</li><li style="box-sizing: border-box; padding: 0px 5px;">122</li><li style="box-sizing: border-box; padding: 0px 5px;">123</li><li style="box-sizing: border-box; padding: 0px 5px;">124</li><li style="box-sizing: border-box; padding: 0px 5px;">125</li><li style="box-sizing: border-box; padding: 0px 5px;">126</li><li style="box-sizing: border-box; padding: 0px 5px;">127</li><li style="box-sizing: border-box; padding: 0px 5px;">128</li><li style="box-sizing: border-box; padding: 0px 5px;">129</li><li style="box-sizing: border-box; padding: 0px 5px;">130</li><li style="box-sizing: border-box; padding: 0px 5px;">131</li><li style="box-sizing: border-box; padding: 0px 5px;">132</li><li style="box-sizing: border-box; padding: 0px 5px;">133</li><li style="box-sizing: border-box; padding: 0px 5px;">134</li><li style="box-sizing: border-box; padding: 0px 5px;">135</li><li style="box-sizing: border-box; padding: 0px 5px;">136</li><li style="box-sizing: border-box; padding: 0px 5px;">137</li><li style="box-sizing: border-box; padding: 0px 5px;">138</li><li style="box-sizing: border-box; padding: 0px 5px;">139</li><li style="box-sizing: border-box; padding: 0px 5px;">140</li><li style="box-sizing: border-box; padding: 0px 5px;">141</li><li style="box-sizing: border-box; padding: 0px 5px;">142</li><li style="box-sizing: border-box; padding: 0px 5px;">143</li></ul><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><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; 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ClientHandler继承自Hanlder，并重写了handleMessage方法，客户端用ClientHandler接收并处理来自于Service的消息。
我们用ClientHandler的实例初始化了clientMessenger。clientMessenger是客户端自身的Messenger，内部指向了ClientHandler的实例，MyService可以通过Message的replyTo得到clientMessenger，从而MyService可以向客户端发送消息，并由ClientHandler接收并处理来自于Service的消息。

分析结果

我们在上述代码的各个关键节点都添加了代码输出语句，我们通过DDMS观察输出结果。

首先打开ClientApp，单击上面的bindService按钮，我们看到DDMS里面的输出结果如下所示: 



我们通过上面的图片可以看出，客户端ClientApp和服务ServiceApp的所属进程PID分别为2524和2542，二者运行在不同的进程中。

我们通过输出结果分析一下代码的执行过程: 

1. 首先我们要明白一点，Messenger是和Handler以及IBinder绑定在一起的。因此Messenger的构造函数有两种： 

a. 一种是传入一个Hanlder，根据传入的Handler创建Messenger，且该Messenger指向该Handler，当我们向Messenger发送信息的时候，Handler会受到信息并处理消息，该构造函数往往是在某个类中构建该类自身的Messenger，比如在MyService中用ServiceHandler的实例初始化了自身的serviceMessenger以及在客户端中用ClientHandler的实例初始化了其自身的clientMessenger。这种Messenger可以看做是本地的Messenger。创建完的Messenger可以通过getBinder()方法得到对应的IBinder类型的实例。 

b. 另一种是传入一个IBinder，根据传入的IBinder实例创建一个远程的Messenger。这种构造函数往往是在客户端中，通过得到Service的onBind方法返回的IBinder，然后基于此IBinder初始化一个远程的Messenger。该Messenger指向的是Service，而不是客户端，所以该Messenger就是一种远程的Messenger。比如客户端中的serviceMessenger就是一种远程的Messenger，指向的是MyService。

2.当单击了客户端中的bindService按钮后，我们通过intent启动了MyService，MyService开始执行其生命周期，先执行onCreate回调方法，然后执行onBind回调方法，在执行onBind方法的时候，该方法返回了MyService中本地serviceMessenger所对应的binder，将其返回给客户端。

3.MyService的onBind方法返回之后，会将IBinder传入客户端的ServiceConnection对象的onServiceConnected回调方法中，该方法的执行表明客户端与MyService建立了连接。此时，我们会根据来自于MyService的IBinder初始化一个指向MyService的serviceMessenger，serviceMessenger是一个远程Messenger。

4.在得到指向MyService的serviceMessenger之后，我们就可以通过它向MyService发送下消息了。我们构建了一个Message，并通过Bundle为其设置了数据，而且需要注意的是，我们还将Message的replyTo设置为客户端的clientMessenger，以便Service可以通过它向客户端发送消息。然后通过代码serviceMessenger.send(msg)将Message发送给MyService。

5.客户端通过serviceMessenger向MyService发送消息后，MyService的ServiceHandler收到消息，并在handleMessage中处理该消息。我们首先读取了该Message的Bundle数据，并打印出来。然后我们通过通过Message的replyTo获取到指向客户端自身的Messenger，并且我们将其保存在了MyService的clientMessenger中，clientMessenger相对于MyService来说是一个远程的Messenger。然后我们又构造了一条Message，并且也通过Bundle设置数据，通过执行代码clientMessenger.send(msgToClient)向客户端回信发送消息。由于我们保存了clientMessenger，所以我们可以在后续的过程中随时向客户端主动发送消息。

6.MyService通过clientMessenger向客户端发信信息后，客户端的ClientHandler收到信息，并在其handleMessage方法中处理消息: 读取来自于MyService的Message的Bundle数据，并将其打印出来。

通过以上的几步我们就能实现客户单与Service的跨进程的双向通信: 

1. 客户端发信息到Service，Service读取信息，即客户端 -> Service 

2. Service给客户端回信，客户端读取信息，即Service -> 客户端

以上就是当我们单击客户端上的bindService按钮所发生的代码执行过程，当我们单击unbindService按钮时，DDMS输出结果如下所示: 



当执行unbindService的时候，客户端与MyService就断开了连接，此时没有其他的客户端连接到MyService上，所以MyService就执行了onUnbind回调方法，然后执行onDestroy回调方法，MyService销毁。

注意事项

在客户端代码中，有两点需要注意: 

1.当通过执行bindService(intent, conn, BIND_AUTO_CREATE)代码的时候，如果intent只设置了action和category，没有明确指明要启动的组件，那么该intent就是是隐式的。在Android 5.0及以上的版本中，必须使用显式的intent去执行启动服务，如果使用隐式的intent，则会报如下错误: 


 
3072-3072/com.ispring.clientapp E/DemoLog﹕ Service Intent must be explicit: Intent { act=com.ispring2.action.MYSERVICE cat=[android.intent.category.DEFAULT] }

解决办法是我们先构建一个隐式的Intent，然后通过PackageManager的resolveService获取可能会被启动的Service的信息。如果ResolveInfo不为空，说明我们能通过上面隐式的Intent找到对应的Service，并且我们还可以获取将要启动的Service的package信息以及类型。然后我们需要将根据得到的Service的包名和类名，构建一个ComponentName，从而设置intent要启动的具体的组件信息，这样intent就从隐式变成了一个显式的intent。然后我们可以将该显式的intent传递给bindService方法去启动服务。 

具体可参见连接：http://stackoverflow.com/questions/24480069/google-in-app-billing-illegalargumentexception-service-intent-must-be-explicit/26318757#26318757。

2.当用Messenger在两个进程之间传递Message时，Message的obj不能设置为设置为non-Parcelable的对象，比如在跨进程的情形下，Message的obj设置为了一个String对象，那么在Messenger执行send(Message)方法时就会报如下错误: 


 
Java.lang.RuntimeException: Can’t marshal non-Parcelable objects
across processes.

解决该问题最简单的办法是，在跨进程的时候不使用Message的obj，用Bundle传递数据，setData设置Bundle数据，getData获取Bundle数据。

希望本文对大家使用Messenger以及与Service的跨进程双向通信有所帮助。

PS：CSDN的Markdown编辑器内嵌的html不支持style吗？设置了style不管用，有知道的请告知一下