class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val homeFragment = HomeFragment()
        val chatListFragment = ChatListFragment()
        val myPageFragment = MyPageFragment()

        val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavigationView)

        //최초 화면을 홈으로 지정
        replaceFragment(homeFragment)

        //하단 네비게이터를 클릭 했을때 발생하는 이벤트 리스너너
        bottomNavigationView.setOnNavigationItemSelectedListener {
            when (it.itemId) {
                R.id.home -> replaceFragment(homeFragment)
                R.id.chatList -> replaceFragment(chatListFragment)
                R.id.myPage -> replaceFragment(myPageFragment)
            }
            true
        }
    }

    //전달 받은 fragment를 fragment컨테이너에 적용
    private fun replaceFragment(fragment: Fragment) {
        supportFragmentManager.beginTransaction()
            .apply {
                replace(R.id.fragmentContainer, fragment)
                commit()
            }
    }
}

class HomeFragment: Fragment(R.layout.fragment_home) {

    private var binding: FragmentHomeBinding? = null
    private lateinit var articleAdapter: ArticleAdapter
    private val auth: FirebaseAuth by lazy {
        Firebase.auth
    }
    private lateinit var articleDB: DatabaseReference
    private lateinit var userDB: DatabaseReference
    private val articleList = mutableListOf<ArticleModel>()

    ...

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        val fragmentHomeBinding = FragmentHomeBinding.bind(view)
        binding = fragmentHomeBinding
        //layout에 fragment_home.xml 맵핑 (gradel 앱단위에서 viewBinding enabled =true 설정)
        ...
    }

    override fun onDestroy() {
        super.onDestroy()

        articleDB.removeEventListener(listener)
    }

    @SuppressLint("NotifyDataSetChanged")
    override fun onResume() {
        super.onResume()
        //뷰를 다시그럼
        articleAdapter.notifyDataSetChanged()
    }
}

fragmentHomeBinding.addFloatingButton.setOnClickListener {
    //context의 safe call을 사용하여 intent에 context에 넣어준다
    context?.let {
        if(auth.currentUser != null){
            val intent = Intent(it,AddArticleActivity::class.java)
            startActivity(intent)
        }else{
            Snackbar.make(view,"로그인 후 사용해주세요", Snackbar.LENGTH_LONG).show()
        }

    }

}