feat: add validation to disable next button

lib/src/auth_screen.dart

@@ -35,9 +35,8 @@ class AuthScreen extends StatefulWidget {
   final String previousBtnTitle;
   final AppBar? customAppBar;
   final Color? customBackgroundColor;
-  final Widget Function(
+  final Widget Function(Future<void> Function()? onPressed, String label,
-          Future<void> Function() onPressed, String label, int step)?
+      int step, bool enabled)? nextButtonBuilder;
-      nextButtonBuilder;
   final Widget? Function(VoidCallback onPressed, String label, int step)?
       previousButtonBuilder;
   final Widget? titleWidget;
@@ -52,6 +51,7 @@ class _AuthScreenState extends State<AuthScreen> {
   final _pageController = PageController();
   final _animationDuration = const Duration(milliseconds: 300);
   final _animationCurve = Curves.ease;
+  bool _formValid = false;
 
   AppBar get _appBar =>
       widget.customAppBar ??
@@ -60,6 +60,7 @@ class _AuthScreenState extends State<AuthScreen> {
       );
 
   void onPrevious() {
+    _validate(_pageController.page!.toInt() - 1);
     _pageController.previousPage(
       duration: _animationDuration,
       curve: _animationCurve,
@@ -95,6 +96,7 @@ class _AuthScreenState extends State<AuthScreen> {
 
       return;
     } else {
+      _validate(_pageController.page!.toInt() + 1);
       _pageController.nextPage(
         duration: _animationDuration,
         curve: _animationCurve,
@@ -102,6 +104,29 @@ class _AuthScreenState extends State<AuthScreen> {
     }
   }
 
+  void _validate(int currentPage) {
+    bool isStepValid = true;
+
+    // Loop through each field in the current step
+    for (var field in widget.steps[currentPage].fields) {
+      for (var validator in field.validators) {
+        String? validationResult = validator(field.value);
+        if (validationResult != null) {
+          // If any validator returns an error, mark step as invalid and break
+          isStepValid = false;
+          break;
+        }
+      }
+      if (!isStepValid) {
+        break; // No need to check further fields if one is already invalid
+      }
+    }
+
+    setState(() {
+      _formValid = isStepValid;
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -136,7 +161,9 @@ class _AuthScreenState extends State<AuthScreen> {
                                 if (field.title != null) ...[
                                   field.title!,
                                 ],
-                                field.build(),
+                                field.build(context, () {
+                                  _validate(i);
+                                }),
                               ],
                             ),
                           )
@@ -197,16 +224,21 @@ class _AuthScreenState extends State<AuthScreen> {
                                   .call(onPrevious, widget.previousBtnTitle, i)!
                             ],
                             widget.nextButtonBuilder?.call(
-                                  () async {
+                                  !_formValid
+                                      ? null
+                                      : () async {
                                           await onNext(widget.steps[i]);
                                         },
                                   widget.steps.last == widget.steps[i]
                                       ? widget.submitBtnTitle
                                       : widget.nextBtnTitle,
                                   i,
+                                  _formValid,
                                 ) ??
                                 ElevatedButton(
-                                  onPressed: () async {
+                                  onPressed: !_formValid
+                                      ? null
+                                      : () async {
                                           await onNext(widget.steps[i]);
                                         },
                                   child: Row(

lib/src/config/registration_options.dart

@@ -28,9 +28,8 @@ class RegistrationOptions {
   final VoidCallback afterRegistration;
   final RegistrationRepository registrationRepository;
   final AppBar Function(String title)? customAppbarBuilder;
-  final Widget Function(
+  final Widget Function(Future<void> Function()? onPressed, String label,
-          Future<void> Function() onPressed, String label, int step)?
+      int step, bool enabled)? nextButtonBuilder;
-      nextButtonBuilder;
   final Widget? Function(VoidCallback onPressed, String label, int step)?
       previousButtonBuilder;
   final Color? backgroundColor;

lib/src/model/auth_bool_field.dart

@@ -24,12 +24,13 @@ class AuthBoolField extends AuthField {
   final Function(String value)? onChange;
 
   @override
-  Widget build() {
+  Widget build(BuildContext context, Function onValueChanged) {
     return FlutterFormInputBool(
       widgetType: widgetType,
       onChanged: (v) {
         value = v;
         onChange?.call(value);
+        onValueChanged();
       },
       validator: (value) {
         for (var validator in validators) {

lib/src/model/auth_drop_down.dart

@@ -24,7 +24,7 @@ class AuthDropdownField extends AuthField {
   final Icon icon;
 
   @override
-  Widget build() {
+  Widget build(BuildContext context, Function onValueChanged) {
     return Padding(
       padding: padding,
       child: DropdownButtonFormField<String>(
@@ -41,6 +41,7 @@ class AuthDropdownField extends AuthField {
         onChanged: (newValue) {
           selectedValue = newValue;
           onChanged(newValue);
+          onValueChanged();
         },
         validator: (value) {
           if (validators.isNotEmpty) {

lib/src/model/auth_field.dart

@@ -7,9 +7,10 @@ import 'package:flutter/material.dart';
 abstract class AuthField<T> {
   AuthField({
     required this.name,
+    required this.value,
+    this.onValueChanged,
     this.title,
     this.validators = const [],
-    required this.value,
   });
 
   final String name;
@@ -17,5 +18,7 @@ abstract class AuthField<T> {
   List<String? Function(T?)> validators;
   T value;
 
-  Widget build();
+  final Function(T)? onValueChanged; // Callback for value changes
+
+  Widget build(BuildContext context, Function onValueChanged);
 }

lib/src/model/auth_pass_field.dart

@@ -27,7 +27,7 @@ class AuthPassField extends AuthField {
   final EdgeInsets padding;
 
   @override
-  Widget build() {
+  Widget build(BuildContext context, Function onValueChanged) {
     return Padding(
       padding: padding,
       child: FlutterFormInputPassword(
@@ -37,6 +37,7 @@ class AuthPassField extends AuthField {
         onChanged: (v) {
           value = v;
           onChange?.call(value);
+          onValueChanged();
         },
         validator: (value) {
           for (var validator in validators) {

lib/src/model/auth_text_field.dart

@@ -28,7 +28,7 @@ class AuthTextField extends AuthField {
   final EdgeInsets padding;
 
   @override
-  Widget build() {
+  Widget build(BuildContext context, Function onValueChanged) {
     return Padding(
       padding: padding,
       child: TextFormField(
@@ -38,6 +38,7 @@ class AuthTextField extends AuthField {
         onChanged: (v) {
           value = v;
           onChange?.call(value);
+          onValueChanged();
         },
         validator: (value) {
           for (var validator in validators) {