01_MainViewModel.kt

class MainViewModel {
  val visible = ObservableBoolean(false)
}

02_main.xml

<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="vm"
            type="MainViewModel"
            />

    </data>
<ImageView
    android:layout_width="50dp"
    android:layout_height="50dp"
    app:viewVisible="@{vm.visible}"
    />
/layout>

03_DatabindingUtil.kt

// ViewModel -> View
@BindingAdapter("viewVisible")
fun viewVisible(v: View, visible: Boolean) {
    if (visible) {
        v.visibility = View.VISIBLE
    } else {
        v.visibility = View.GONE
    }
}

// Databinding -> ViewModel, viewVisibleAttrChanged.onChange() 가 호출되면 리턴 값이 ViewModel 로 바인딩됨
@InverseBindingAdapter(attribute = "viewVisible", event = "viewVisibleAttrChanged")
fun viewVisible(v: View): Boolean {
    return v.visibility == View.VISIBLE
}

// View -> Databinding, View 에 변화가 생기면 viewVisibleAttrChanged 이벤트로 등록된 InverseBindingAdapter 함수를 호출
@BindingAdapter("viewVisibleAttrChanged", requireAll = false)
fun viewVisibleChanged(v: View, newAttrChanged: InverseBindingListener) {
    newAttrChanged.onChange()
}