layout.kt

//ActivityViewModel.kt
private val _textToShow = MutableLiveData<String>()

val textToShow : LiveData<String>()
  get() = textToShow

fun buttonClicked(){
  _textToShow.value = "Hello"
}

//layout.xml
<?xml version="1.0" encoding="utf-8"?>
<layout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
        <variable
                name="viewModel"
                type="com.example.android.app.ui.viewmodels.ActivityViewModel"/>
    </data>

<LinearLayout
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation:"vertical">
  <Button
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="@string/press_btn"
          style="@style/normalButton"
          android:id="@+id/button"
          android:onClick="@{()->viewModel.buttonClicked()}"/>
  <TextView
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="@{viewModel.textToShow}"/>
</LinearLayout>
</layout>