android kotlin - EditText password validation

Android Kotlin - EditText Password Validation (Breakdown)

This code demonstrates password validation for an EditText field in an Android application written in Kotlin. Here's a breakdown of the functionalities:

  1. Layout and References:

    • The activity_main.xml file defines the user interface with an EditText for password input and a TextView to display password requirements.
    • In MainActivity.kt, the onCreate function retrieves references to these UI elements using findViewById.

  2. Password Rules:

    • The textView displays the password requirements: minimum length of 8 characters, containing at least one uppercase letter, one number, and one special character.

  3. Password Validation with TextWatcher:

    • A TextWatcher is added to the editText. This listener gets triggered whenever the text in the edit text changes.
    • Inside the onTextChanged method, the code checks if the entered text is a valid password using the isValidPassword extension function and if its length is at least 8 characters.
      • If valid, the error message on the editText is cleared.
      • If invalid, an error message "invalid password" is set on the editText.

  4. Password Validation Function:

    • The isValidPassword extension function takes a CharSequence (which can be a String) as input.
    • It uses a regular expression (passwordPattern) to define the password format. This pattern ensures the password has:
      • At least one digit ([0-9])
      • At least one uppercase letter ([A-Z])
      • At least one special character ([@#$%^&+=!]))
      • No whitespace characters (\\S+$)
      • Minimum length of 4 characters (.{4,}$)
    • The function compiles the pattern and uses a matcher to check if the input matches the defined format. It returns true if the password is valid and false otherwise.

Summary

This code effectively implements password validation for an EditText field in an Android app. It leverages a TextWatcher to monitor user input and validates the password against a defined pattern using regular expressions. This approach ensures secure password creation by enforcing complexity requirements.


MainActivity.kt 

package com.cfsuman.kotlintutorials

import android.app.Activity
import android.os.Bundle
import android.text.Editable
import android.text.TextWatcher
import android.widget.EditText
import android.widget.TextView
import java.util.regex.Pattern


class MainActivity : Activity() {
    private lateinit var editText:EditText
    private lateinit var textView:TextView

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

        // get the widgets reference from XML layout
        editText = findViewById(R.id.editText)
        textView = findViewById(R.id.textView)

        // 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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#DCDCDC"
    android:padding="32dp">

    <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>
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