Android 使用binder访问service的方式

蹉跎莫遣韶光老，人生唯有读书好。这篇文章主要讲述Android 使用binder访问service的方式相关的知识，希望能为你提供帮助。
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 [email protected] * */ 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. this.unbindService(mSc); } }

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"); Messenger messenger = new Messenger(service); Message msg = new Message(); msg.what = RemoteService.MSG_SAY_HELLO; msg.replyTo = messenger_reciever; try { messenger.send(msg); } 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) { return messager.getBinder(); }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); } }}; Messengermessager = 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。
【Android 使用binder访问service的方式】demo 源码可以在这里下载源代码下载