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Android ApiDemos示例解析(39):App->Service->Local Service Binding

本例和下列Local Service Controller 的Activity代码都定义在LocalServiceActivities.Java 中,作为LocalServiceActivities 内部类实现的。 调用的Service为LocalService。

LocalService既可以做为“Started” Service,也可以做为”Bound” Service。

一个“Bound” Service 可以通过Client/Service模式提供Service。它运行应用程序组件(比如Activity)与之绑定,然后接受请求并返回响应或者提供进程间通信机制,它的生命周期通常与调用它的组件(如Activity)相同。 而对于LocalService即作为“Started” Service又作为“Bound”Service,如果LocalService已作为“Started” Service启动,中即使所有Client都断开与它的绑定,LocalService也不会停止。

如果一个Service需要作为“Bound”Service运行其它组件与之绑定,就必须实现onBind方法。这个方法返回一个IBound对象给Client。Client可以通过这个IBind对象来调用Service的方法。

Client可以通过bindService来实现与“Bound”Service的绑定,Service 与 Client 的绑定是异步实现的,因此Client 需要通过 ServiceConnection 接口来监视与Service之间的连接。 Client 调用bindService 时,bindService 立即返回,之后当Android系统为Client 和Service之间建立起链接后调用 ServiceConnection 的 onServiceConnection 来通知Client 与Service之间的链接建立成功,并给Client返回 Service 提供的IBind对象。

LocalService 只提供给同一个Application的组件使用,不提供进程间通信接口,因此只需要派生一个Binder的子类如果直接的函数调用接口。

[java]
// Class for clients to access.  Because we know  
 // this service always runs in the same process as  
 //its clients, we don't need to deal with IPC.  
public class LocalBinder extends Binder { 
 LocalService getService() { 
 return LocalService.this; 
 } 

// Class for clients to access.  Because we know
 // this service always runs in the same process as
 //its clients, we don't need to deal with IPC.
public class LocalBinder extends Binder {
 LocalService getService() {
 return LocalService.this;
 }
}
LocalBinder只提供了一个方法getService ,返回LocalService 对象自身。

LocalService的 onBind方法定义:

[java] 
@Override 
public IBinder onBind(Intent intent) { 
 return mBinder; 

  
// This is the object that receives interactions from clients.  See  
// RemoteService for a more complete example.  
private final IBinder mBinder = new LocalBinder(); 
@Override
public IBinder onBind(Intent intent) {
 return mBinder;
}
 
// This is the object that receives interactions from clients.  See
// RemoteService for a more complete example.
private final IBinder mBinder = new LocalBinder();
onBind的返回值为mBinder 为 LocalBinder类对象。它定义了一个方法getService。

再来看看Client类 LocalServiceActivities.Binding 的实现:

[java]
private LocalService mBoundService; 
  
private ServiceConnection mConnection = new ServiceConnection() { 
 public void onServiceConnected(ComponentName className, IBinder service) { 
 // This is called when the connection with the service has been  
 // established, giving us the service object we can use to  
 // interact with the service.  Because we have bound to a explicit  
 // service that we know is running in our own process, we can  
 // cast its IBinder to a concrete class and directly access it.  
 mBoundService = ((LocalService.LocalBinder)service).getService(); 
  
 // Tell the user about this for our demo.  
 Toast.makeText(Binding.this, R.string.local_service_connected, 
 Toast.LENGTH_SHORT).show(); 
 } 
  
 public void onServiceDisconnected(ComponentName className) { 
 // This is called when the connection with the service has been  
 // unexpectedly disconnected -- that is, its process crashed.  
 // Because it is running in our same process, we should never  
 // see this happen.  
 mBoundService = null; 
 Toast.makeText(Binding.this, R.string.local_service_disconnected, 
 Toast.LENGTH_SHORT).show(); 
 } 
}; 
private LocalService mBoundService;
 
private ServiceConnection mConnection = new ServiceConnection() {
 public void onServiceConnected(ComponentName className, IBinder service) {
 // This is called when the connection with the service has been
 // established, giving us the service object we can use to
 // interact with the service.  Because we have bound to a explicit
 // service that we know is running in our own process, we can
 // cast its IBinder to a concrete class and directly access it.
 mBoundService = ((LocalService.LocalBinder)service).getService();
 
 // Tell the user about this for our demo.
 Toast.makeText(Binding.this, R.string.local_service_connected,
 Toast.LENGTH_SHORT).show();
 }
 
 public void onServiceDisconnected(ComponentName className) {
 // This is called when the connection with the service has been
 // unexpectedly disconnected -- that is, its process crashed.
 // Because it is running in our same process, we should never
 // see this happen.
 mBoundService = null;
 Toast.makeText(Binding.this, R.string.local_service_disconnected,
 Toast.LENGTH_SHORT).show();
 }
};
mConnection定义了ServiceConnection接口,onServiceConnected ,onServiceDisconnected分别在Service与Client 之间建立链接和断开链接时调用。其中IBinder service 就是 Service 的onBind的返回对象。 这里将其通过类型转换为LocalService也就是mBoundService。

Client 通过调用bindService建立与Service之间的绑定:

[java] 
bindService(new Intent(Binding.this, 
 LocalService.class), mConnection, Context.BIND_AUTO_CREATE); 
bindService(new Intent(Binding.this,
 LocalService.class), mConnection, Context.BIND_AUTO_CREATE);
如果需要断开与Service之间的绑定,则调用unbindService.

[java] www.zzzyk.com
unbindService(mConnection); 
unbindService(mConnection);[java] view plaincopyprint?
<p>如果你熟悉Socket编程, Client 绑定”Bound”Service 的方法和使用Socket通信非常类似。</p><p><a href=/2012/0630/20120630034121506.png"><img class="aligncenter size-full wp-image-1254" title="20110514001" alt="" src=/2012/0630/20120630034121506.png" width="339" height="501" /></a></p> 
<p>如果你熟悉Socket编程, Client 绑定”Bound”Service 的方法和使用Socket通信非常类似。</p><p><a href=/2012/0630/20120630034121506.png"><img class="aligncenter size-full wp-image-1254" title="20110514001" alt="" src=/2012/0630/20120630034121506.png" width="339" height="501" /></a></p>

作者:mapdigit
 

 

补充:移动开发 , Android ,
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