【项目总结】-Android Service用法总结

Android Service组件在后台不可见，但一般情况下是与其他组件一同运行在一个进程中的（Local Service与其他部分在一个进程，Remote Service单独开进程），而且在主线程中，并不单独启动一个线程（除非程序员自己另外开线程）

Service组件提供了后台执行某些功能以及为其他应用程序提供服务，提供支撑功能的能力。

生命周期：OnCreate()->OnStartCommand()->OnDestroy()。

调用 Context.startService()可以多次调用，但只要调用stopService一次就会stop.多次调用startService或者bindService不会启动多个服务。

local service样例

public class LocalService extends Service {
    private NotificationManager mNM;

    // Unique Identification Number for the Notification.
    // We use it on Notification start, and to cancel it.
    private int NOTIFICATION = R.string.local_service_started;

    /**
     * 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;
        }
    }

    @Override
    public void onCreate() {
        mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);

        // Display a notification about us starting.  We put an icon in the status bar.
        showNotification();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i("LocalService", "Received start id " + startId + ": " + intent);
        // We want this service to continue running until it is explicitly
        // stopped, so return sticky.
        return START_STICKY;
    }

    @Override
    public void onDestroy() {
        // Cancel the persistent notification.
        mNM.cancel(NOTIFICATION);

        // Tell the user we stopped.
        Toast.makeText(this, R.string.local_service_stopped, Toast.LENGTH_SHORT).show();
    }

    @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();

    /**
     * Show a notification while this service is running.
     */
    private void showNotification() {
        // In this sample, we'll use the same text for the ticker and the expanded notification
        CharSequence text = getText(R.string.local_service_started);

        // Set the icon, scrolling text and timestamp
        Notification notification = new Notification(R.drawable.stat_sample, text,
                System.currentTimeMillis());

        // The PendingIntent to launch our activity if the user selects this notification
        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
                new Intent(this, LocalServiceActivities.Controller.class), 0);

        // Set the info for the views that show in the notification panel.
        notification.setLatestEventInfo(this, getText(R.string.local_service_label),
                       text, contentIntent);

        // Send the notification.
        mNM.notify(NOTIFICATION, notification);
    }
}

调用

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();
    }
};

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;
}

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

@Override
protected void onDestroy() {
    super.onDestroy();
    doUnbindService();
}

在Activity中通过mBoundService调用Service中的public方法来获取后台数据，实际上onServiceConnected中返回的是一个IBinder对象，只不过我们在此已经确定Local Service

已经在执行了，可以进行强制类型转换。

Local Service可以通过发送广播来给前台提供后台数据更新，前台只需要注册一个Receiver既可以与Service通讯。

例子：

后台Service的某个方法进行数据更新后执行

Intent intent = new Intent("XXXX_Message");

sendBroadcast(intent); 通知前台数据已经更新

前台

private MessageReceiver receiver;

class MessageReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context arg0, Intent arg1) {
String action = arg1.getAction();
if (action.equals("XXXX_Message")) {
//从Service接收广播消息
String msgStr = arg1.getStringExtra("msg_str");
}
}
}



@Override
protected void onResume() {

super.onResume();

IntentFilter filter = new IntentFilter("XXXX_Message");
if (receiver == null)
receiver = new MessageReceiver();
//注册BroadcastReceiver
registerReceiver(receiver, filter);
}



@Override
protected void onPause() {
unregisterReceiver(receiver);
super.onPause();
}