Kotlin Fragment

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

        setFrag(0)

        btn_fragment1.setOnClickListener {
            setFrag(0)
        }
        btn_fragment2.setOnClickListener {
            setFrag(1)
        }
        btn_fragment3.setOnClickListener {
            setFrag(2)
        }
    }

    private fun setFrag(fragNum : Int) {
        // Fragment 연결
        val ft = supportFragmentManager.beginTransaction()
        when(fragNum){
            0 -> {
                ft.replace(R.id.main_frame, Fragment1()).commit()
            }
            1 -> {
                ft.replace(R.id.main_frame, Fragment2()).commit()
            }
            2 -> {
                ft.replace(R.id.main_frame, Fragment3()).commit()
            }
        }
    }
}

// activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

// char_list.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_margin="16dp">
        <Button
            android:id="@+id/btn_fragment1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Fragment1"/>
        <Button
            android:id="@+id/btn_fragment2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Fragment2"/>
        <Button
            android:id="@+id/btn_fragment3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Fragment3"/>
    </LinearLayout>
    <FrameLayout
        android:id="@+id/main_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="16dp"/>
</LinearLayout>

// Fragement1, 2, 3.kt
class Fragment1 : Fragment() {
    override fun onCreateView( // Fragment 첫 실행시 수행
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // frag.xml 연결 (1,2,3)
        val view = inflater.inflate(R.layout.frag1, container, false)
        return view
    }
}