创建未绑定的服务

首先要做的是将服务添加到 AndroidManifest.xml 标签内的 AndroidManifest.xml：

<application ...>

    ...        

    <service
        android:name=".RecordingService"
        <!--"enabled" tag specifies Whether or not the service can be instantiated by the system — "true" -->
        <!--if it can be, and "false" if not. The default value is "true".-->
        android:enabled="true"
        <!--exported tag specifies Whether or not components of other applications can invoke the -->
        <!--service or interact with it — "true" if they can, and "false" if not. When the value-->
        <!--is "false", only components of the same application or applications with the same user -->
        <!--ID can start the service or bind to it.-->
        android:exported="false" />

</application>

如果你打算在单独的包中管理服务类（例如：.AllServices.RecordingService），那么你需要指定服务的位置。因此，在上述情况下，我们将修改：

android:name=".RecordingService"

至

android:name=".AllServices.RecordingService"

或者最简单的方法是指定完整的包名称。

然后我们创建实际的服务类：

public class RecordingService extends Service {
    private int NOTIFICATION = 1; // Unique identifier for our notification

    public static boolean isRunning = false;
    public static RecordingService instance = null;

    private NotificationManager notificationManager = null;

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate(){
        instance = this;
        isRunning = true;

        notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

        super.onCreate();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId){
        // The PendingIntent to launch our activity if the user selects this notification
        PendingIntent contentIntent = PendingIntent.getActivity(this, 0, new Intent(this, MainActivity.class), 0);

        // Set the info for the views that show in the notification panel.
        Notification notification = new NotificationCompat.Builder(this)
                .setSmallIcon(R.mipmap.ic_launcher)        // the status icon
                .setTicker("Service running...")           // the status text
                .setWhen(System.currentTimeMillis())       // the time stamp
                .setContentTitle("My App")                 // the label of the entry
                .setContentText("Service running...")      // the content of the entry
                .setContentIntent(contentIntent)           // the intent to send when the entry is clicked
                .setOngoing(true)                          // make persistent (disable swipe-away)
                .build();

        // Start service in foreground mode
        startForeground(NOTIFICATION, notification);

        return START_STICKY;
    }

    @Override
    public void onDestroy(){
        isRunning = false;
        instance = null;

        notificationManager.cancel(NOTIFICATION); // Remove notification

        super.onDestroy();
    }

    public void doSomething(){
        Toast.makeText(getApplicationContext(), "Doing stuff from service...", Toast.LENGTH_SHORT).show();
    }

}

所有这些服务都在运行时显示通知，并且在调用 doSomething() 方法时可以显示 toasts。

正如你将注意到的，它被实现为单例 ，跟踪它自己的实例 - 但是没有通常的静态单例工厂方法，因为服务是自然的单例并且是由意图创建的。该实例对于外部有用，可以在服务运行时获得服务的句柄。

最后，我们需要从活动中启动和停止服务：

public void startOrStopService(){
    if( RecordingService.isRunning ){
        // Stop service
        Intent intent = new Intent(this, RecordingService.class);
        stopService(intent);
    }
    else {
        // Start service
        Intent intent = new Intent(this, RecordingService.class);
        startService(intent);
    }
}

在此示例中，服务以相同的方法启动和停止，具体取决于它的当前状态。

我们也可以从我们的活动中调用 doSomething() 方法：

public void makeServiceDoSomething(){
    if( RecordingService.isRunning )
        RecordingService.instance.doSomething();
}