กดปุ่มแล้วจะแสดง dialog ถ้าตอบ Yes จะเปลี่ยนสี background ของ activity นี้เป็นสีแดง

ไฟล์ที่เกี่ยวข้อง

• activity_main.xml
• MainActivity.kt

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/layoutRoot"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

    <Button
            android:id="@+id/btnShowAlert"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Show Alert"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

package com.phaisarn.myapplication

import android.graphics.Color
import android.os.Bundle
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.app.AlertDialog
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // when button is clicked, show the alert
        btnShowAlert.setOnClickListener {
            // Initialize a new instance of
            val builder = AlertDialog.Builder(this@MainActivity)

            // Set the alert dialog title
            builder.setTitle("App background color")

            // Display a message on alert dialog
            builder.setMessage("Are you want to set the app background color to RED?")

            // Set a positive button and its click listener on alert dialog
            builder.setPositiveButton("YES") { _, _ ->
                // Do something when user press the positive button
                Toast.makeText(applicationContext, "Ok, we change the app background.", Toast.LENGTH_SHORT).show()

                // Change the app background color
                layoutRoot.setBackgroundColor(Color.RED)
            }

            // Display a negative button on alert dialog
            builder.setNegativeButton("No") { _, _ ->
                Toast.makeText(applicationContext, "You are not agree.", Toast.LENGTH_SHORT).show()
            }

            // Display a neutral button on alert dialog
            builder.setNeutralButton("Cancel") { _, _ ->
                Toast.makeText(applicationContext, "You cancelled the dialog.", Toast.LENGTH_SHORT).show()
            }

            // Finally, make the alert dialog using builder
            val dialog: AlertDialog = builder.create()

            // Display the alert dialog on app interface
            dialog.show()
        }
    }
}

Link

• android kotlin – AlertDialog example