Android Basic Alert Dialog Box

Alert tutorial.

First, your XML layout should include an id for the ConstraintLayout.

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mainLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".MainActivity"
    tools:showIn="@layout/activity_main">

</androidx.constraintlayout.widget.ConstraintLayout>

The critical part is the android:id="@+id/mainLayout". Don't forget it. It has an id of mainLayout.

Next, we need to write some Kotlin code. It's not too difficult, just type this:

        Snackbar.make(mainLayout, "Updated 3h ago", Snackbar.LENGTH_INDEFINITE).show()