1<?xml version="1.0" encoding="utf-8"?> 2<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" 3 xmlns:app="http://schemas.android.com/apk/res-auto" 4 xmlns:tools="http://schemas.android.com/tools" 5 android:layout_width="match_parent" 6 android:layout_height="match_parent" 7 tools:context=".MainActivity"> 8 9 <TextView 10 android:layout_width="wrap_content" 11 android:layout_height="wrap_content" 12 android:text="Hello World!" 13 android:id="@+id/textView" 14 app:layout_constraintBottom_toBottomOf="parent" 15 app:layout_constraintLeft_toLeftOf="parent" 16 app:layout_constraintRight_toRightOf="parent" 17 app:layout_constraintTop_toTopOf="parent" /> 18 19</android.support.constraint.ConstraintLayout>