【起航計劃 034】2015 起航計劃 Android APIDemo的魔鬼步伐 33 App->Service->Local Service Binding 綁定服務 ServiceConnecti

本例和下列Local Service Controller 的Activity代碼都定義在LocalServiceActivities.Java 中，做爲LocalServiceActivities 內部類實現的。 調用的Service爲LocalService。

LocalService既能夠作爲「Started」 Service，也能夠作爲」Bound」 Service。

一個「Bound」 Service 能夠經過Client/Service模式提供Service。它運行應用程序組件（好比Activity）與之綁定，而後接受請求並返回響應或者提供進 程間通訊機制，它的生命週期一般與調用它的組件（如Activity）相同。 而對於LocalService即做爲「Started」 Service又做爲「Bound」Service，若是LocalService已做爲「Started」 Service啓動，中即便全部Client都斷開與它的綁定，LocalService也不會中止。

若是一個Service須要做爲「Bound」Service運行其它組件與之綁定，就必須實現onBind方法。這個方法返回一個IBound對象給Client。Client能夠經過這個IBind對象來調用Service的方法。

Client能夠經過bindService來實現與「Bound」Service的綁定，Service 與 Client 的綁定是異步實現的，所以Client 須要經過 ServiceConnection 接口來監視與Service之間的鏈接。 Client 調用bindService 時，bindService 當即返回，以後當Android系統爲Client 和Service之間創建起連接後調用 ServiceConnection 的 onServiceConnection 來通知Client 與Service之間的連接創建成功，並給Client返回 Service 提供的IBind對象。

LocalService 只提供給同一個Application的組件使用，不提供進程間通訊接口，所以只須要派生一個Binder的子類若是直接的函數調用接口。

// 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只提供了一個方法getService ，返回LocalService 對象自身。

LocalService的 onBind方法定義：

    @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的返回值爲mBinder 爲 LocalBinder類對象。它定義了一個方法getService。

再來看看Client類 LocalServiceActivities.Binding 的實現:

        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定義了ServiceConnection接口，onServiceConnected ，onServiceDisconnected分別在Service與Client 之間創建連接和斷開連接時調用。其中IBinder service 就是 Service 的onBind的返回對象。 這裏將其經過類型轉換爲LocalService也就是mBoundService。

 

Client 經過調用bindService創建與Service之間的綁定：

        void doBindService() {
            // Establish a connection with the service.  We use an explicit
            // class name because we want a specific service implementation that
            // we know will be running in our own process (and thus won't be
            // supporting component replacement by other applications).
            bindService(new Intent(Binding.this, 
                    LocalService.class), mConnection, Context.BIND_AUTO_CREATE);
            mIsBound = true;
        }

 

若是須要斷開與Service之間的綁定，則調用unbindService.

        void doUnbindService() {
            if (mIsBound) {
                // Detach our existing connection.
                unbindService(mConnection);
                mIsBound = false;
            }
        }

 

若是你熟悉Socket編程, Client 綁定」Bound」Service 的方法和使用Socket通訊很是相似。