override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    Log.d("MainActivity", "onCreate: ");

    supportFragmentManager.beginTransaction().add(R.id.container, homeFragment)  //沒有.commit()
    supportFragmentManager.beginTransaction().add(R.id.container, dashboardFragment).commit()
    supportFragmentManager.beginTransaction().add(R.id.container, notificationFragment).commit()
}