<?xml version="1.0" encoding="utf-8"?> // ➊
<androidx.constraintlayout.widget.ConstraintLayout // ➋
    xmlns:android="http://schemas.android.com/apk/res/android" // ➋
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent" // ➌
    android:layout_height="match_parent" // ➌
    tools:context=".MainActivity">
    <TextView // ➍
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" /> // ➍

</androidx.constraintlayout.widget.ConstraintLayout>