//开启服务做兼容处理
Intent intentOne = new Intent(this, BackService.class);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    startForegroundService(intentOne);
}else {
    startService(intentOne);
}

public void onCreate() {
    super.onCreate();
    if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.O){
        NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
       //数字是随便写的“40”，
        nm.createNotificationChannel(new NotificationChannel("40", "App Service", NotificationManager.IMPORTANCE_DEFAULT));
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, "40");

               //其中的2，是也随便写的，正式项目也是随便写
        startForeground(2 ,builder.build());
    }
  
}