android kotlin - EditText password validation

MainActivity.kt


package com.example.jetpack

import android.os.Bundle
import android.text.Editable
import android.text.TextWatcher
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import java.util.regex.Pattern


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


        // show password rules in text view
        textView.text = "Password minimum length 8"
        textView.append("\n1 uppercase")
        textView.append("\n1 number")
        textView.append("\n1 special character")


        // add text changed listener for edit text
        editText.addTextChangedListener(object: TextWatcher{
            override fun beforeTextChanged(s: CharSequence?,
                                           start: Int, count: Int, after: Int) {

            }

            override fun onTextChanged(s: CharSequence?,
                                       start: Int, before: Int, count: Int) {
                s?.apply {
                    // check user input a valid formatted password
                    if (isValidPassword() && toString().length>=8) {
                        editText.error == null
                    }else{
                        // show error on input invalid password
                        editText.error = "invalid password."
                    }
                }
            }
            override fun afterTextChanged(s: Editable?) {

            }
        })
    }
}


// extension function to validate password rules/patterns
fun CharSequence.isValidPassword(): Boolean {
    val passwordPattern = "^(?=.*[0-9])(?=.*[A-Z])(?=.*[@#$%^&+=!])(?=\\S+$).{4,}$"
    val pattern = Pattern.compile(passwordPattern)
    val matcher = pattern.matcher(this)
    return matcher.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="textPassword"
        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" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="12dp"
        android:fontFamily="sans-serif-condensed-medium"
        android:gravity="center"
        android:padding="8dp"
        android:textColor="#4F42B5"
        android:textSize="22sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText"
        tools:text="TextView" />

</androidx.constraintlayout.widget.ConstraintLayout>