How to Make an Alert Dialog Fill Majority of the Screen Size in Android?

An Alert Dialog is a window that appears on the screen to give notifications to the user, make some decisions for the user, or enter some information from the user. An Alert Dialog is generally not full screen, but in this article, we’ll be implementing something similar.

Building an Alert Dialog:

1. Title: This area gives title to the alert dialog 
2. Description: This area gives the main message of the alert dialog
3. Action button: This area deals with the decision of the user after reading the description

Step By Step Implementation

Step 1: Create a New Project in Android Studio

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. The code for that has been given in both Java and Kotlin Programming Language for Android.

Step 2: Working with activity_main.xml

Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file. 

XML

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:background="#00FF00">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Open Gift"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

Step 3: Working with the MainActivity File

Go to the MainActivity File and refer to the following code. Below is the code for the MainActivity File. Comments are added inside the code to understand the code in more detail.

Java

import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.WindowManager;
import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // for changing the background color of title bar
        ActionBar aBar = getSupportActionBar();
        ColorDrawable cd = new ColorDrawable(Color.parseColor("#FF00FF00"));
        if (aBar != null) {
            aBar.setBackgroundDrawable(cd);
        }

        // using onClickListener on button
        findViewById(R.id.button).setOnClickListener(v -> {

            // builds alert dialog
            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);

            // description of alert dialog
            builder.setMessage("Welcome to GeeksForGeeks!");

            // Title of alert dialog
            builder.setTitle("Gift !");

            builder.setCancelable(false);

            // Action button of alert dialog for cancel dialog and come to homepage
            builder.setPositiveButton("Great, see again!", (dialog, which) -> dialog.cancel());

            // Action button of alert dialog  for exit app
            builder.setNegativeButton("Exit", (dialog, which) -> finish());
            AlertDialog alertDialog = builder.create();

            // show alert dialog
            alertDialog.show();

            DisplayMetrics displayMetrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
            WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams();
            layoutParams.copyFrom(alertDialog.getWindow().getAttributes());

            // setting width to 90% of display
            layoutParams.width = (int) (displayMetrics.widthPixels * 0.9f);

            // setting height to 90% of display
            layoutParams.height = (int) (displayMetrics.heightPixels * 0.9f);
            alertDialog.getWindow().setAttributes(layoutParams);
        });
    }
}

Kotlin

import android.graphics.Color
import android.graphics.drawable.ColorDrawable
import android.os.Bundle
import android.util.DisplayMetrics
import android.view.View
import android.view.WindowManager
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity

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

        // for changing the background color of title bar
        val aBar = supportActionBar
        val cd = ColorDrawable(Color.parseColor("#FF00FF00"))
        aBar?.setBackgroundDrawable(cd)

        // using onClickListener on button
        findViewById<View>(R.id.button).setOnClickListener {

            // builds alert dialog
            val builder = AlertDialog.Builder(this)

            // description of alert dialog
            builder.setMessage("Welcome to GeeksForGeeks!")

            // Title of alert dialog
            builder.setTitle("Gift !")
            builder.setCancelable(false)

            // Action button of alert dialog for cancel dialog and come to homepage
            builder.setPositiveButton("Great, see again!") { dialog, which -> dialog.cancel() }

            // Action button of alert dialog  for exit app
            builder.setNegativeButton("Exit") { dialog, which -> finish() }

            val alertDialog = builder.create()

            // show alert dialog
            alertDialog.show()

            val displayMetrics = DisplayMetrics()
            windowManager.defaultDisplay.getMetrics(displayMetrics)
            val layoutParams = WindowManager.LayoutParams()
            layoutParams.copyFrom(alertDialog.window?.attributes)

            // setting width to 90% of display
            layoutParams.width = (displayMetrics.widthPixels * 0.9f).toInt()

            // setting height to 90% of display
            layoutParams.height = (displayMetrics.heightPixels * 0.9f).toInt()
            alertDialog.window?.attributes = layoutParams
        }
    }
}

Output: