android kotlin - AlertDialog example

Step 1. Create a class MainActivity.kt

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // Set a click listener for button widget
        button.setOnClickListener{
            val builder = AlertDialog.Builder(this@MainActivity)
            builder.setTitle("App background color")
            builder.setMessage("Are you want to set the app background color to RED?")
            builder.setPositiveButton("YES"){dialog, which ->
                Toast.makeText(applicationContext,"Ok, we change the app background.",Toast.LENGTH_SHORT).show()
             
                root_layout.setBackgroundColor(Color.RED)
            }
            builder.setNegativeButton("No"){dialog,which ->
                Toast.makeText(applicationContext,"You are not agree.",Toast.LENGTH_SHORT).show()
            }
            builder.setNeutralButton("Cancel"){_,_ ->
                Toast.makeText(applicationContext,"You cancelled the dialog.",Toast.LENGTH_SHORT).show()
            }
            val dialog: AlertDialog = builder.create()
            dialog.show()
        }
    }
}

Step 2. create a layout activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/root_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    >
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Show Me Alert Dialog"
        />
</LinearLayout>