val myDialog = Dialog(this)
        myDialog.setContentView(R.layout.my_dialog)
        myDialog.setTitle("My Dialog!")
        myDialog.setCancelable(true)
        myDialog.show()

<?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">

<TextView
        android:text="Hello world!"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/textView"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:textSize="30sp"/>

</android.support.constraint.ConstraintLayout>

myDialog.create()