How to validate Email Address in Android on EditText using Kotlin?

This example demonstrates how to validate Email Address in Android on EditText using Kotlin.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/relativeLayout"
   android:layout_width="match_parent"
   android:layout_height="match_parent">
   <TextView
      android:id="@+id/textView"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="70dp"
      android:background="#008080"
      android:padding="5dp"
      android:text="TutorialsPoint"
      android:textColor="#fff"
      android:textSize="24sp"
      android:textStyle="bold" />
   <EditText
      android:id="@+id/editText"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true"
      android:layout_margin="20dp"
      android:hint="Enter Email id" />
   <Button
      android:id="@+id/text"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@+id/editText"
      android:layout_centerInParent="true"
      android:text="Check validation"
      android:textAlignment="center"
      android:textColor="#000"
      android:textSize="18sp" />
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.kt
import android.os.Bundle
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   lateinit var button: Button
   lateinit var emailId: EditText
   var emailPattern = "[a-zA-Z0-9._-]+@[a-z]+\\.+[a-z]+"
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      button = findViewById(R.id.text)
      emailId = findViewById(R.id.editText)
      button.setOnClickListener {
         if (emailId.text.toString().isEmpty()) {
            Toast.makeText(applicationContext, "enter email address", Toast.LENGTH_SHORT).show()
         }
         else {
            if (emailId.text.toString().trim { it <= ' ' }.matches(emailPattern.toRegex())) {
               Toast.makeText(applicationContext, "valid email address", Toast.LENGTH_SHORT).show()
            }
            else {
               Toast.makeText(applicationContext, "Invalid email address", Toast.LENGTH_SHORT).show()
            }
         }
      }
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.q11">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen