class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        
        super.onCreate(savedInstanceState)  // 현재 UI를 일단 저장해둠
        setContentView(R.layout.activity_main)  // R.layout.activity_main이 View 타입 반환
    }
}

val intent = Intent(this, SubActivity::class.java)
startActivity(intent)

val intent = Intent(Intent.ACTION_DIAL)
val TEST_DIAL_NUMBER = Uri.fromParts("tel", "5551212", null)
intent.data = TEST_DIAL_NUMBER
startActivity(intent)

// 뷰바인딩 적용
class RecyclerActivity : AppCompatActivity() {
    private lateinit var binding: ActivityRecyclerBinding       // Activity 이름에 걸맞게 타입을 적어줘야 함

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityRecyclerBinding.inflate(layoutInflater)    // 여기도 마찬가지
        setContentView(binding.root)        // 여기도 변경

    }
}

 private var _binding: ResultProfileBinding? = null
    // This property is only valid between onCreateView and
    // onDestroyView.
    private val binding get() = _binding!!

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        _binding = ResultProfileBinding.inflate(inflater, container, false)
        val view = binding.root
        return view
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

package com.example.android_study

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.Fragment
import com.example.android_study.databinding.ActivityChangeFragmentBinding
import com.example.android_study.databinding.FragmentMyBinding

class ChangeFragmentActivity : AppCompatActivity() {

    private lateinit var binding : ActivityChangeFragmentBinding
    private lateinit var myFragment: MyFragment
    private lateinit var mySecondFragment: MySecondFragment

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityChangeFragmentBinding.inflate(layoutInflater)

        setContentView(binding.root)

        binding.fragmentChangeBtn1.setOnClickListener {
            myFragment = MyFragment.newInstance("hohohoho", "dfsfs")
            supportFragmentManager.beginTransaction().replace(R.id.activity_change_frame_layout, myFragment).commit()
        }

        binding.fragmentChangeBtn2.setOnClickListener {
            mySecondFragment = MySecondFragment.newInstance("hohohohoasfslkadjf", "Asdfsa")
            supportFragmentManager.beginTransaction().replace(R.id.activity_change_frame_layout, mySecondFragment).commit()
        }
    }
}

package com.example.android_study

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.example.android_study.databinding.FragmentMyBinding

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [MyFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class MyFragment : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null


    private var _binding: FragmentMyBinding? = null
    private val binding get() = _binding!!

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment

        _binding = FragmentMyBinding.inflate(inflater, container, false)
        return binding.root       ?
    }

    override fun onDestroyView() {
        _binding = null     // Fragment가 없어질 때 _binding을 null 처리함
        super.onDestroyView()
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        binding.textview.text = param1

//        super.onViewCreated(view, savedInstanceState)
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment MyFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            MyFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

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

        val et_id = findViewById<EditText>(R.id.et_id)
        val et_pw = findViewById<EditText>(R.id.et_pw)

        // 키보드의 엔터가 눌렸을 때 이벤트 처리하기 위한 코드
        et_pw.setOnEditorActionListener() { v, actionId, event ->
            if(actionId == EditorInfo.IME_ACTION_DONE){// 엔터가 눌렸다면
                Login(v) // 아래 정의한 함수를 호출하라
                true     // 반환 타입은 boolean
            } else {
                false   // 반환 타입은 boolean
            }
        }
    }

    fun Login(v: View){

        // 키보드 숨기기
        var imm = getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
        imm.hideSoftInputFromWindow(v.windowToken, 0)

        Log.d(TAG, "Login: 로그인 성공")
        Toast.makeText(this, "로그인 성공", Toast.LENGTH_LONG).show()
    }
}

class MainActivity : AppCompatActivity() {
    lateinit var et_id:EditText
    lateinit var et_pw:EditText

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

        et_id = findViewById<EditText>(R.id.et_id)
        et_pw = findViewById<EditText>(R.id.et_pw)

        // 아이디, 비밀번호가 저장되어 있다면 불러오고 그렇지 않으면 빈칸으로 세팅함
        // onCreate에서 이렇게 구현하면 한번만 로그인에 성공했던 디바이스의 경우 매번 로그인정보가 불러와지는 효과를 가진다
        var pref = this.getPreferences(0)
        et_id.setText(pref.getString("아이디", ""))
        et_pw.setText(pref.getString("비밀번호", ""))

        et_pw.setOnEditorActionListener() { v, actionId, event ->
            if(actionId == EditorInfo.IME_ACTION_DONE){
                Login(v)
                true
            } else {
                false
            }
        }
    }

    fun Login(v: View){
        if(et_id.text.toString() == "hojun" && et_pw.text.toString() =="0303"){
            Toast.makeText(this, "로그인 성공", Toast.LENGTH_LONG).show()
            var editor = this.getPreferences(0).edit()
            editor.putString("아이디", "hojun").apply()
            editor.putString("비밀번호", "0303").apply()
        }

        else{
            Toast.makeText(this, "로그인 실패", Toast.LENGTH_LONG).show()
        }

        // 키보드 숨기기
        var imm = getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
        imm.hideSoftInputFromWindow(v.windowToken, 0)
    }


}