Android | Alert Dialog Box and How to create it

Alert Dialog shows the Alert message and gives the answer in the form of yes or no. Alert Dialog displays the message to warn you and then according to your response the next step is processed.

Android Alert Dialog is built with the use of three fields: Title, Message area, Action Button.
Alert Dialog code has three methods:

setTitle() method for displaying the Alert Dialog box Title
setMessage() method for displaying the message
setIcon() method is use to set the icon on Alert dialog box.

Then we add the two Button, setPositiveButton and setNegativeButton to our Alert Dialog Box as shown below.

Example:

Below are the steps for Creating the Alert Dialog Android Application:

Step 1: Create a new project. After that, you have java and XML file.
Step 2: Open your XML file and then add TextView for message as shown below (you can change it accordingly).
Step 3: Now, open up the activity java file. After, on create method declaration, the onbackpressed method is called when you click the back button of your device.
Step 4: Create the object of Builder class Using AlertDialog.Builder. Now, set the Title, message.
Step 5: In a builder object set the positive Button now gives the button name and add the OnClickListener of DialogInterface. Same as with the negative Button, at last, create the Alert dialog Box with builder object and then show the Alert Dialog.
Step 6: Now if positive button press finish the app goto outside from the app if negative then finish the dialog box

Step 7: Now run it and then press the back button. After that click Yes or No Button.

The complete code of MainActivity.java or activity_main.xml of Alert Dialog is given below:

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout 
    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=".MainActivity"> 
  
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Press The Back Button of Your Phone."
    android:textStyle="bold"
    android:textSize="30dp"
    android:gravity="center_horizontal"
    android:layout_marginTop="180dp"
    /> 
  
</RelativeLayout> 

MainActivity.java

package org.geeksforgeeks.navedmalik.alertdialog; 
  
import android.content.DialogInterface; 
import android.support.v7.app.AlertDialog; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
  
public class MainActivity extends AppCompatActivity { 
  
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.activity_main); 
    } 
  
    // Declare the onBackPressed method 
    // when the back button is pressed 
    // this method will call 
    @Override
    public void onBackPressed() 
    { 
  
        // Create the object of 
        // AlertDialog Builder class 
        AlertDialog.Builder builder 
            = new AlertDialog 
                  .Builder(MainActivity.this); 
  
        // Set the message show for the Alert time 
        builder.setMessage("Do you want to exit ?"); 
  
        // Set Alert Title 
        builder.setTitle("Alert !"); 
  
        // Set Cancelable false 
        // for when the user clicks on the outside 
        // the Dialog Box then it will remain show 
        builder.setCancelable(false); 
  
        // Set the positive button with yes name 
        // OnClickListener method is use of 
        // DialogInterface interface. 
  
        builder 
            .setPositiveButton( 
                "Yes", 
                new DialogInterface 
                    .OnClickListener() { 
  
                        @Override
                        public void onClick(DialogInterface dialog, 
                                            int which) 
                        { 
  
                            // When the user click yes button 
                            // then app will close 
                            finish(); 
                        } 
                    }); 
  
        // Set the Negative button with No name 
        // OnClickListener method is use 
        // of DialogInterface interface. 
        builder 
            .setNegativeButton( 
                "No", 
                new DialogInterface 
                    .OnClickListener() { 
  
                        @Override
                        public void onClick(DialogInterface dialog, 
                                            int which) 
                        { 
  
                            // If user click no 
                            // then dialog box is canceled. 
                            dialog.cancel(); 
                        } 
                    }); 
  
        // Create the Alert dialog 
        AlertDialog alertDialog = builder.create(); 
  
        // Show the Alert Dialog box 
        alertDialog.show(); 
    } 
} 

Output:

My Personal Notes

activity_main.xml

MainActivity.java

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