main_landscape.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
    android:id="@+id/constraint_layout"
>


    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 1"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_margin="4dp"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 2"
        app:layout_constraintLeft_toRightOf="@+id/button1"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_margin="4dp"
       />

</android.support.constraint.ConstraintLayout>

main_portrait.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
    android:id="@+id/constraint_layout"
>


    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 1"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_margin="4dp"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 2"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button1"
        android:layout_margin="4dp"
       />

</android.support.constraint.ConstraintLayout>

MainActivity.kt

import android.content.res.Configuration
import android.os.Bundle
import android.support.constraint.ConstraintSet
import android.support.v7.app.AppCompatActivity
import android.transition.ChangeBounds
import android.transition.TransitionManager
import kotlinx.android.synthetic.main.main_landscape.*

class MainActivity : AppCompatActivity() {

    val portraitConstraintSet = ConstraintSet()
    val landscapeConstraintSet = ConstraintSet()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // load portrait and layout constraint sets
        // they need to have the same items inside the <ConstraintLayout/>, just with different constraints
        portraitConstraintSet.clone(this,R.layout.main_portrait)
        landscapeConstraintSet.clone(this,R.layout.main_landscape)

        // start with the correct layout for the current orientation
        val orientation = resources.configuration.orientation
        if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
            setContentView(R.layout.main_landscape)
        }
        else {
            setContentView(R.layout.main_portrait)
        }
        
    }

    override fun onConfigurationChanged(configuration: Configuration?) {
        super.onConfigurationChanged(configuration)
        // we only want a changebounds transition, no fading
        val transition = ChangeBounds()
        // default duration is too small to see, so bump it up to 600ms
        transition.duration = 600
        TransitionManager.beginDelayedTransition(constraint_layout,transition)
        if (configuration?.orientation == Configuration.ORIENTATION_PORTRAIT) {
            portraitConstraintSet.applyTo(constraint_layout)
        }
        if (configuration?.orientation == Configuration.ORIENTATION_LANDSCAPE) {
            landscapeConstraintSet.applyTo(constraint_layout)
        }
    }

}