MainActivity.kt
package com.example.jetpack
import android.os.Bundle
import android.text.Editable
import android.text.TextWatcher
import android.util.Patterns
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// add text changed listener for edit text
editText.addTextChangedListener(object: TextWatcher{
override fun beforeTextChanged(p0: CharSequence?,
p1: Int, p2: Int, p3: Int) {
}
override fun onTextChanged(p0: CharSequence?,
p1: Int, p2: Int, p3: Int) {
// check inputted text that it is a valid email address or not
if (p0.isValidEmail()){
editText.error = null
}else{
editText.error = "Invalid email."
}
}
override fun afterTextChanged(p0: Editable?) { }
})
}
}
// extension function to validate edit text inputted email address
fun CharSequence?.isValidEmail():Boolean{
return !isNullOrEmpty() && Patterns.EMAIL_ADDRESS.matcher(this).matches()
}
activity_main.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:id="@+id/constraintLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FEFEFA"
tools:context=".MainActivity">
<EditText
android:id="@+id/editText"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="12dp"
android:layout_marginEnd="12dp"
android:padding="12dp"
android:textSize="30sp"
android:inputType="textEmailAddress"
android:fontFamily="sans-serif-condensed-medium"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.12" />
</androidx.constraintlayout.widget.ConstraintLayout>


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