Looking at the Android view system

The traditional approach to building Android UIs is to define component trees and modify them during runtime. While this can be done completely programmatically, the preferred way is to create layout files. They use XML tags and attributes to define which UI elements should be presented on screen. Let's take a look:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="match_parent">
  <TextView
    android:id="@+id/message"
    style="@style/TextAppearance.AppCompat.Medium"
    android:layout_width="wrap_content"
 ...