Kotlin Android AlertDialog

Android AlertDialog is a subclass of Dialog class. It is used to prompt a small dialog window to make a decision before a user can proceed in the same activity without changing the screen. A dialog shows the title, message, up to three buttons or a custom layout.
The instance of AlertDialog.Builder class is used to make an alert dialog. Through alert dialog, we create positive (yes), negative (no) and neutral (cancel) decision.

Kotlin Android AlertDialog Example

In this example, we prompt an alert dialog window by clicking a button. This dialog window sets three decision actions as positive, negative and neutral.

activity_main.xml

Add the following code in the activity_main.xml file. In this layout file, we add a button to prompt an alert dialog.

< ?xml version="1.0" encoding="utf-8"?>  
< android.support.constraint.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:layout_width="match_parent"  
    android:layout_height="match_parent"  
    tools:context="example.javatpoint.com.kotlinalertdialog.MainActivity">  
  
    < Button  
        android:id="@+id/button"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_marginBottom="8dp"  
        android:layout_marginEnd="8dp"  
        android:layout_marginStart="8dp"  
        android:layout_marginTop="8dp"  
        android:text="@string/button"  
        app:layout_constraintBottom_toBottomOf="parent"  
        app:layout_constraintEnd_toEndOf="parent"  
        app:layout_constraintStart_toStartOf="parent"  
        app:layout_constraintTop_toTopOf="parent" />  
  
< /android.support.constraint.ConstraintLayout>  

strings.xml

In the strings.xml file add the following code.

< resources>  
    < string name="app_name">Kotlin AlertDialog< /string>  
    < string name="button">click button< /string>  
    < string name="dialogTitle">Delete File< /string>  
    < string name="dialogMessage">Deleting file may be harm your system< /string>  
  
< /resources>  

MainActivity.kt

Add the following code in the MainActivity.kt class. The instance of AlertDialog.Builder class call the setTitle(), setMessage(), setIcon() methods to set the dialog title, message, icon respectively.
To set the action on alert dialog call the setPositiveButton(), setNeutralButton() and setNegativeButton() methods for positive, neutral and negative action respectively. The show() method of AlertDialog.Builder is used to display the alert dialog.

package example.javatpoint.com.kotlinalertdialog  
  
import android.support.v7.app.AppCompatActivity  
import android.os.Bundle  
import android.support.v7.app.AlertDialog  
import android.widget.Button  
import android.widget.Toast  
  
class MainActivity : AppCompatActivity() {  
  
    override fun onCreate(savedInstanceState: Bundle?) {  
        super.onCreate(savedInstanceState)  
        setContentView(R.layout.activity_main)  
  
        val button = findViewById< Button>(R.id.button)  
  
        button.setOnClickListener {  
            val builder = AlertDialog.Builder(this)  
            //set title for alert dialog  
            builder.setTitle(R.string.dialogTitle)  
            //set message for alert dialog  
            builder.setMessage(R.string.dialogMessage)  
            builder.setIcon(android.R.drawable.ic_dialog_alert)  
  
            //performing positive action  
            builder.setPositiveButton("Yes"){dialogInterface, which ->  
                Toast.makeText(applicationContext,"clicked yes",Toast.LENGTH_LONG).show()  
            }  
            //performing cancel action  
            builder.setNeutralButton("Cancel"){dialogInterface , which ->  
                Toast.makeText(applicationContext,"clicked cancel\n operation cancel",Toast.LENGTH_LONG).show()  
            }  
            //performing negative action  
            builder.setNegativeButton("No"){dialogInterface, which ->  
                Toast.makeText(applicationContext,"clicked No",Toast.LENGTH_LONG).show()  
            }  
            // Create the AlertDialog  
            val alertDialog: AlertDialog = builder.create()  
            // Set other dialog properties  
            alertDialog.setCancelable(false)  
            alertDialog.show()  
        }  
    }  
}