Learning Concurrency in Kotlin

Adding UI elements

Now we can start adding some UI elements to do some testing. First, let's update the layout of MainActivity, which is located in res/layout/activity_main.xml. For now, just adding a ProgressBar will do, so let's replace the contents of the ConstraintLayout so that a ProgressBar is located in the middle of the screen:

<android.support.constraint.ConstraintLayout ...>    <ProgressBar        android:id="@+id/progressBar"        style="?android:attr/progressBarStyle"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent" /></android.support.constraint.ConstraintLayout> ...