android kotlin - EditText allow only characters

MainActivity.kt


package com.example.jetpack

import android.os.Bundle
import android.text.InputFilter
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)

        // allow only characters/alphabets/letters with white space
        // programmatically accepts both uppercase and lowercase letters
        editText2.filters = arrayOf(filter)
    }
}


// input filter to allow only characters and whitespace
val filter = InputFilter { charSequence, i, i2, spanned, i3, i4 ->
    if (charSequence == "") { // for backspace
        return@InputFilter charSequence
    }
    if (charSequence.toString().matches("[a-zA-Z ]+".toRegex())) {
        charSequence
    } else ""
}

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">

    <!-- allow only characters and whitespace in xml -->
    <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:digits="abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        android:inputType="text|textVisiblePassword"
        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" />

    <EditText
        android:id="@+id/editText2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="12dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="12dp"
        android:inputType="text|textVisiblePassword"
        android:padding="12dp"
        android:textSize="30sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText" />

</androidx.constraintlayout.widget.ConstraintLayout>