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Android 使用binder访问service的方式
binder机制是贯穿整个Android系统的进程间访问机制，经常被用来访问service，我们结合代码看一下binder在访问service的情形下是怎么具体使用的。
service 你可以理解成没有的界面的activity，它是跑在后台的程序，所谓后台是相对于可以被看得到的程序的，后台程序是不能直接交互的程序。
binder主要是用来进程间通信的，但也可用在和本地service通信。
1. 我们先来看一个与本地service通信的例子。
package com.ckt.wangxin;import android.app.Service;import android.content.Intent;import android.os.Binder;import android.os.IBinder;import android.widget.Toast;/** * This is a service stub for both LocalBinderClient * and RemoteBinderClient * @author Wang Xin * @email springnap@163.com * */public class LocalService extends Service { @Override public IBinder onBind(Intent intent) { return new LocalBinder(); } public void sayHelloWorld(){ Toast.makeText(this.getApplicationContext(), "Hello World Local Service!", Toast.LENGTH_SHORT).show(); } public class LocalBinder extends Binder { LocalService getService() { // Return this instance of LocalService so clients can call public methods return LocalService.this; } } }
local servcie 的代码如上，在onBinder方法中返回binder，binder包含了service的句柄，客户端得到句柄以后就可以调用servcie的公共方法了，这种调用方式是最常见的。
客户端代码
package com.ckt.wangxin;import android.app.Activity;import android.content.ComponentName;import android.content.Context;import android.content.Intent;import android.content.ServiceConnection;import android.os.Bundle;import android.os.IBinder;import android.util.Log;import com.ckt.wangxin.LocalService.LocalBinder;public class LocalServiceTestActivity extends Activity { static final String TAG = "LocalBinderTestActivity"; ServiceConnection mSc; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mSc = new ServiceConnection(){ @Override public void onServiceConnected(ComponentName name, IBinder service) { Log.d(TAG, "service connected"); LocalService ss = ((LocalBinder)service).getService(); ss.sayHelloWorld(); } @Override public void onServiceDisconnected(ComponentName name) { Log.d(TAG, "service disconnected"); } }; } @Override protected void onStart() { super.onStart(); Log.d(TAG, this.getApplicationContext().getPackageCodePath()); Intent service = new Intent(this.getApplicationContext(),LocalService.class); this.bindService(service, mSc, Context.BIND_AUTO_CREATE); } @Override protected void onStop() { super.onStop(); //must unbind the service otherwise the ServiceConnection will be leaked. <span style="color: rgb(255, 0, 0); ">this.unbindService(mSc);</span> }}
需要注意的是在onStop中要解绑定service, 否则会造成内存泄露的问题。
2. 我们再看一下与另外一个进程中的service进行通信的问题（跨进程通信！）。
如何将servcie运行在另外一个进程呢？在manifest 里面配置个属性就行了。
android:process=":remote" , 代表这个service运行在同一个应用程序的不同进程中。
<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.ckt.wangxin" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="15" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".LocalServiceTestActivity" android:label="@string/app_name" > <!-- <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> --> </activity> <service android:name=".LocalService"></service> <!-- android:process=":remote" specify this service run in another process in the same application. --> <service android:name=".RemoteService" android:process=":remote"></service> <activity android:name="RemoteServiceTestActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application></manifest>
客户端可以使用Messenger发送消息到service。
客户端代码：
package com.ckt.wangxin;import android.app.Activity;import android.content.ComponentName;import android.content.Context;import android.content.Intent;import android.content.ServiceConnection;import android.os.Bundle;import android.os.Handler;import android.os.IBinder;import android.os.Message;import android.os.Messenger;import android.os.RemoteException;import android.util.Log;import android.widget.Toast;public class RemoteServiceTestActivity extends Activity { static final String TAG = "RemoteServiceTestActivity"; ServiceConnection mSc; public static final int SAY_HELLO_TO_CLIENT = 0; /** * Handler of incoming messages from service. */ class IncomingHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case SAY_HELLO_TO_CLIENT: Toast.makeText(RemoteServiceTestActivity.this.getApplicationContext(), "Hello World Remote Client!", Toast.LENGTH_SHORT).show(); break; default: super.handleMessage(msg); } } } Messenger messenger_reciever = new Messenger(new IncomingHandler()); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mSc = new ServiceConnection(){ @Override public void onServiceConnected(ComponentName name, IBinder service) { Log.d(TAG, "service connected"); <span style="color: rgb(204, 0, 0); ">Messenger messenger = new Messenger(service); Message msg = new Message(); msg.what = RemoteService.MSG_SAY_HELLO;</span> msg.replyTo = messenger_reciever; try { <span style="color: rgb(255, 0, 0); ">messenger.send(msg);</span> } catch (RemoteException e) { e.printStackTrace(); } } @Override public void onServiceDisconnected(ComponentName name) { Log.d(TAG, "service disconnected"); } }; } @Override protected void onStart() { super.onStart(); Log.d(TAG, this.getApplicationContext().getPackageCodePath()); Intent service = new Intent(this.getApplicationContext(),RemoteService.class); this.bindService(service, mSc, Context.BIND_AUTO_CREATE); } @Override protected void onStop() { super.onStop(); //must unbind the service otherwise the ServiceConnection will be leaked. this.unbindService(mSc); }}
获得service端传来的binder，用来构建一个Messenger向service发送消息。
service端代码：
package com.ckt.wangxin;import android.app.Service;import android.content.Intent;import android.os.Handler;import android.os.IBinder;import android.os.Message;import android.os.Messenger;import android.os.RemoteException;import android.widget.Toast;public class RemoteService extends Service { public static final int MSG_SAY_HELLO = 0; @Override public IBinder onBind(Intent intent) { <span style="color: rgb(204, 0, 0); "> return messager.getBinder();</span> } Handler IncomingHandler = new Handler() { @Override public void handleMessage(Message msg) { if(msg.replyTo != null){ Message msg_client = this.obtainMessage(); msg_client.what = RemoteServiceTestActivity.SAY_HELLO_TO_CLIENT; try { ((Messenger)msg.replyTo).send(msg_client); } catch (RemoteException e) { // TODO Auto-generated catch block e.printStackTrace(); } } switch (msg.what) { case MSG_SAY_HELLO: Toast.makeText(RemoteService.this.getApplicationContext(), "Hello World Remote Service!", Toast.LENGTH_SHORT).show(); break; default: super.handleMessage(msg); } } }; Messenger messager = new Messenger (IncomingHandler);}
构建一个Messenger，包含一个handler，然后将messenger的binder传给客户端，客户端可以通过handler再构造一个messenger与service通信，消息在handler里面被处理。
现在是service端单向响应客户端的消息，同理可以做成双向发送消息，实现双向通信。
demo 源码可以在这里下载 源代码下载
Android 使用binder访问service的方式
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