app 수준 gradle의 plugins에 >> id 'kotlin-kapt' << 추가해줘야함

[BindingAdapter] 안드로이드 DataBinding에 BindingAdapter 사용법

class MainActivity2 : AppCompatActivity() {
    private lateinit var binding: ActivityMain2Binding
    val liveText = MutableLiveData<String>()
    val liveVisible = MutableLiveData<Boolean>()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main2)
        binding.apply {
            lifecycleOwner =
                this@MainActivity2 // **중요** binding에 LifeCycleOwner을 지정해줘야 LiveData가 실시간으로 변화
            activity = this@MainActivity2 // xml 파일에 선언한 activity
        }

        binding.btnChange1.setOnClickListener {
            liveVisible.value = true
        }
        binding.btnChange2.setOnClickListener {
            liveVisible.value = false
        }
        liveText.value = "Hello DataBinding"

    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout 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>">

    <data>

        <variable
            name="activity"
            type="com.example.mutablelivedata.MainActivity2" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <TextView
            android:id="@+id/text_view"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{activity.liveText}"
            **app:visible**="@{activity.liveVisible}"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toTopOf="@id/btn_change1"
            app:layout_constraintVertical_chainStyle="packed"/>

        <Button
            android:id="@+id/btn_change1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="visible"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/text_view"
            app:layout_constraintBottom_toTopOf="@id/btn_change2"/>

        <Button
            android:id="@+id/btn_change2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="gone"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/btn_change1"
            app:layout_constraintBottom_toBottomOf="parent"/>

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

object DataAdatper {

    /**
     * View의 visibility를 변경
     * @param view 속성을 사용하는 view
     * @param isVisible visibility를 변경시키는 기준이 되는 값
     */
    @JvmStatic
    @BindingAdapter("visible")
    fun setVisible(view: View, isVisible: Boolean) {
        view.visibility = if (isVisible) View.VISIBLE else View.GONE
    }
}