rj_form_engine

A schema-driven form engine for Flutter. Build complex, validated forms from pure configuration — no boilerplate, no repetitive wiring.

pub package pub points License: MIT

Why rj_form_engine?

Building forms in Flutter is repetitive. Every screen has the same patterns — text fields, dropdowns, date pickers, image uploads — all wired up by hand, validated manually, and state-managed individually.

rj_form_engine replaces all of that with a schema. You define what your form looks like. The engine renders it, validates it, and returns the data.

RjForm(
  fields: [
    FieldMeta(key: 'name',    label: 'Full Name',     type: FieldType.text,     required: true),
    FieldMeta(key: 'dob',     label: 'Date of Birth', type: FieldType.date),
    FieldMeta(key: 'country', label: 'Country',       type: FieldType.dropdown,
      dropdownSource: DropdownSource.async(fetchCountries),
    ),
    FieldMeta(key: 'city',    label: 'City',          type: FieldType.dropdown,
      dependency: FieldDependency(dependsOn: 'country'), // cascades automatically
      dropdownSource: DropdownSource.async(
        ({parentValue}) async => fetchCities(parentValue: parentValue),
      ),
    ),
  ],
  onSubmit: (result) async {
    print(result.values); // {'name': 'John', 'dob': DateTime(...), ...}
  },
)

Features

  • 13 field types — text, number, date, dropdown, textarea, image upload, slider, time picker, spinner, toggle, radio, chip multi-select, custom
  • Custom fields — inject any widget via FieldMeta.custom
  • Cascading dropdowns — parent/child dependency with auto-reload and auto-clear
  • Async dropdown loading — load items from APIs, databases, or caches
  • Static dropdowns — pass a fixed list when no async call is needed
  • 25+ built-in validators — email, phone, URL, password rules, date ranges, and more
  • Conditional visibility — show/hide fields based on other field values
  • View / edit modes — render read-only with a single flag
  • Pre-fill values — for edit or clone mode
  • External controller — read form state from outside the widget
  • onChanged callback — react to individual field changes in real time
  • Error summary — display all validation errors at the top of the form
  • Keyboard dismissal — Tap outside fields to dismiss the keyboard.
  • Accessibility — Semantics labels on all field widgets
  • Custom date/time formats — use dateFormat and timeFormat on FieldMeta
  • Typed field config — SliderConfig, DateConfig, ImageConfig, and more via FieldConfig
  • Themeable — one RjFormTheme controls all field styles
  • Minimal dependencies — only flutter SDK + image_picker
  • State-management agnostic — works with Provider, Riverpod, Bloc, GetX, or nothing at all

📸 Preview

Video Demo

See the engine in action, including dynamic validation, cascading logic, and smooth field transitions:

https://github.com/user-attachments/assets/420abb19-a3e8-4ae9-b4c7-3b6e0881237c

Screenshots

Default Fields Automatic Error Handling Dark/Custom Theme
Custom Fields Support Form Entry Page

Installation

Add to your pubspec.yaml:

dependencies:
  rj_form_engine: ^0.2.1

Then run:

flutter pub get

Quick Start

A minimal form with validation in under 20 lines:

import 'package:rj_form_engine/rj_form_engine.dart';

RjForm(
  fields: [
    FieldMeta(
      key: 'email',
      label: 'Email Address',
      type: FieldType.text,
      required: true,
      hint: 'Enter your email',
      validators: [RjValidators.email()],
    ),
    FieldMeta(
      key: 'age',
      label: 'Age',
      type: FieldType.number,
      required: true,
      validators: [RjValidators.min(18, message: 'Must be 18 or older')],
    ),
  ],
  onSubmit: (result) async {
    final email = result.get<String>('email');
    final age   = result.get<num>('age');
    // Send to your backend
  },
)

Complete Example

A registration form demonstrating multiple field types, cascading dropdowns, conditional visibility, and custom validation:

import 'package:rj_form_engine/rj_form_engine.dart';

class RegistrationForm extends StatelessWidget {
  const RegistrationForm({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Registration')),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(16),
        child: RjForm(
          fields: [
            // Section header
            FieldMeta.section(key: 'personal_info', label: 'Personal Information'),

            // Text field
            FieldMeta(
              key: 'full_name',
              label: 'Full Name',
              type: FieldType.text,
              required: true,
              hint: 'John Doe',
              validators: [RjValidators.minLength(2)],
            ),

            // Email with validation
            FieldMeta(
              key: 'email',
              label: 'Email',
              type: FieldType.text,
              required: true,
              validators: [RjValidators.email()],
            ),

            // Password with rules
            FieldMeta(
              key: 'password',
              label: 'Password',
              type: FieldType.text,
              required: true,
              obscureText: true,
              validators: [
                RjValidators.minLength(8),
                RjValidators.hasUppercase(),
                RjValidators.hasDigit(),
                RjValidators.hasSpecialChar(),
              ],
            ),

            // Date picker
            FieldMeta(
              key: 'dob',
              label: 'Date of Birth',
              type: FieldType.date,
              required: true,
              dateFormat: 'dd/MM/yyyy',
              validators: [RjValidators.pastDate()],
            ),

            // Section header
            FieldMeta.section(key: 'location', label: 'Location'),

            // Async dropdown (country)
            FieldMeta(
              key: 'country',
              label: 'Country',
              type: FieldType.dropdown,
              required: true,
              dropdownSource: DropdownSource.async(
                ({parentValue}) async => fetchCountries(),
              ),
            ),

            // Cascading dropdown (city — depends on country)
            FieldMeta(
              key: 'city',
              label: 'City',
              type: FieldType.dropdown,
              required: true,
              dependency: FieldDependency(dependsOn: 'country'),
              dropdownSource: DropdownSource.async(
                ({parentValue}) async => fetchCities(parentValue: parentValue),
              ),
            ),

            // Conditional field — only shows when country == 'bd'
            FieldMeta(
              key: 'nid_number',
              label: 'NID Number',
              type: FieldType.text,
              dependency: FieldDependency(
                dependsOn: 'country',
                condition: (value) => value == 'bd',
              ),
              validators: [RjValidators.digitsOnly()],
            ),

            // Radio buttons
            FieldMeta(
              key: 'gender',
              label: 'Gender',
              type: FieldType.radio,
              required: true,
              options: const [
                DropdownItem(id: 'male', label: 'Male'),
                DropdownItem(id: 'female', label: 'Female'),
                DropdownItem(id: 'other', label: 'Other'),
              ],
            ),

            // Chip multi-select
            FieldMeta(
              key: 'interests',
              label: 'Interests',
              type: FieldType.chip,
              options: const [
                DropdownItem(id: 'tech', label: 'Technology'),
                DropdownItem(id: 'sports', label: 'Sports'),
                DropdownItem(id: 'music', label: 'Music'),
                DropdownItem(id: 'travel', label: 'Travel'),
              ],
              validators: [RjValidators.minSelect(1, message: 'Select at least one')],
            ),

            // Toggle
            FieldMeta(
              key: 'accept_terms',
              label: 'Accept Terms & Conditions',
              type: FieldType.toggle,
              required: true,
            ),
          ],
          onSubmit: (result) async {
            // result.values contains all field data
            await registerUser(result.values);
          },
          onSuccess: (result) {
            ScaffoldMessenger.of(context).showSnackBar(
              const SnackBar(content: Text('Registration successful!')),
            );
          },
          showErrorsSummary: true,
          theme: RjFormTheme(
            primaryColor: const Color(0xFF2563EB),
            borderRadius: BorderRadius.circular(10),
          ),
        ),
      ),
    );
  }

  Future<List<DropdownItem>> fetchCountries() async {
    // Replace with your API call
    return const [
      DropdownItem(id: 'bd', label: 'Bangladesh'),
      DropdownItem(id: 'us', label: 'United States'),
      DropdownItem(id: 'uk', label: 'United Kingdom'),
    ];
  }

  Future<List<DropdownItem>> fetchCities({String? parentValue}) async {
    // Replace with your API call
    final cities = {
      'bd': [const DropdownItem(id: 'dhaka', label: 'Dhaka')],
      'us': [const DropdownItem(id: 'nyc', label: 'New York')],
      'uk': [const DropdownItem(id: 'london', label: 'London')],
    };
    return cities[parentValue] ?? [];
  }

  Future<void> registerUser(Map<String, dynamic> data) async {
    // Replace with your API call
    await Future.delayed(const Duration(seconds: 1));
    print('Registered: $data');
  }
}

Core Concepts

FieldMeta

FieldMeta is the blueprint for a single form field. Every field in your form is defined by one FieldMeta instance.

Property Type Description
key String Required. Unique identifier for the field. Used to read/write values.
label String Required. Display label shown above the field.
type FieldType Required. Determines which widget is rendered.
required bool When true, the field must have a non-empty value to pass validation.
validators List<FieldValidator> Additional validation functions. See Validation.
hint String? Placeholder text displayed inside the field.
dependency FieldDependency? Controls visibility based on another field's value. See Dependencies.
dropdownSource DropdownSource? Item source for dropdown fields. Accepts static or async data.
options List<DropdownItem> Options for radio and chip fields.
config FieldConfig? Typed configuration (e.g., SliderConfig, DateConfig). Takes precedence over flat params.
viewOnly bool When true, renders the field as read-only.
builder CustomFieldBuilder? Custom widget builder for FieldType.custom.

Typed config (preferred over flat params):

// Slider with typed config
FieldMeta(
  key: 'volume',
  label: 'Volume',
  type: FieldType.slider,
  config: const SliderConfig(min: 0.0, max: 100.0, divisions: 10),
),

// Date with typed config
FieldMeta(
  key: 'deadline',
  label: 'Deadline',
  type: FieldType.date,
  config: DateConfig(
    firstDate: DateTime.now(),
    lastDate: DateTime.now().add(const Duration(days: 365)),
    format: 'yyyy-MM-dd',
  ),
),

FormController

FormController manages form state externally. It extends ChangeNotifier and works with any state management approach.

final _controller = FormController();

@override
void dispose() {
  _controller.dispose();
  super.dispose();
}

// Read values at any time
print(_controller.values);

// Validate programmatically
if (_controller.validate(fields)) {
  final result = _controller.toResult();
  // handle result
}

// Set or clear values
_controller.setValue('name', 'John');
_controller.clear();

When to use an external controller:

  • Submit from outside the form (e.g., AppBar action, FAB)
  • Enable/disable a button based on form state
  • Auto-save on field changes
  • Reset the form programmatically

Validation

Validation happens in two layers:

  1. required: true — built-in check for null, empty strings, and empty lists.
  2. validators — a list of FieldValidator functions that run after the required check.

Each validator returns String? — an error message if invalid, or null if valid.

FieldMeta(
  key: 'password',
  label: 'Password',
  type: FieldType.text,
  required: true,
  validators: [
    RjValidators.minLength(8),
    RjValidators.hasUppercase(),
    RjValidators.hasDigit(),
    RjValidators.hasSpecialChar(),
    RjValidators.custom(
      (value) => value.toString().contains('123')
          ? 'Password must not contain "123"'
          : null,
    ),
  ],
),

Available validators:

Validator Description
required() Non-null, non-empty check
email() Email format
url() HTTP/HTTPS URL format
phone() International phone (7-15 digits)
bdPhone() Bangladeshi mobile number
minLength(n) / maxLength(n) String length bounds
lengthBetween(min, max) String length range
min(n) / max(n) Numeric value bounds
between(min, max) Numeric range
positive() / nonNegative() Positive / non-negative numbers
hasUppercase() / hasLowercase() / hasDigit() / hasSpecialChar() Password rule checks
pattern(regex) Custom regex
lettersOnly() / digitsOnly() / alphanumeric() Character type checks
pastDate() / futureDate() Date range checks
minSelect(n) / maxSelect(n) Multi-select bounds
matches(other) Value matching (e.g., confirm password)
custom(fn) Wrap any custom validation logic

Note: All validators except required() skip null/empty values. Combine them with required: true to enforce presence.

Conditional Visibility & Dependencies

Fields can be shown or hidden based on other field values using FieldDependency:

// Show only when 'reason' equals 'other'
FieldMeta(
  key: 'other_reason',
  label: 'Please specify',
  type: FieldType.textArea,
  dependency: FieldDependency(
    dependsOn: 'reason',
    condition: (value) => value == 'other',
  ),
),

Cascading dropdowns use the same mechanism. When the parent dropdown changes, the child automatically reloads its items and clears its current value:

FieldMeta(
  key: 'city',
  label: 'City',
  type: FieldType.dropdown,
  dependency: FieldDependency(dependsOn: 'country'),
  dropdownSource: DropdownSource.async(
    ({parentValue}) async => fetchCities(parentValue: parentValue),
  ),
),

Custom Fields

Use FieldMeta.custom to embed any widget into your form. The builder receives the full FieldMeta, current value, an onChanged callback, and any error text:

FieldMeta.custom(
  key: 'rating',
  label: 'Rating',
  required: true,
  validators: [(v) => v == null ? 'Please select a rating' : null],
  builder: (context, field, value, onChanged, errorText) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Text(field.label, style: const TextStyle(fontWeight: FontWeight.w500)),
        StarRatingWidget(
          value: value as int? ?? 0,
          onChanged: onChanged,
        ),
        if (errorText != null)
          Padding(
            padding: const EdgeInsets.only(top: 4),
            child: Text(errorText, style: const TextStyle(color: Colors.red, fontSize: 12)),
          ),
      ],
    );
  },
),

Field Types

Type Widget Returns Common Use
FieldType.text RjTextField String Names, emails, passwords
FieldType.number RjNumberField num? Age, price, quantity
FieldType.date RjDateField DateTime Birth dates, deadlines
FieldType.dropdown RjDropdownField String? (item id) Country, category, status
FieldType.textArea RjTextField String Descriptions, comments
FieldType.image RjImageField List<String> (file paths) Photo uploads
FieldType.slider RjSliderField double Volume, rating, range
FieldType.timePicker RjTimePickerField TimeOfDay Meeting time, schedule
FieldType.spinner RjSpinnerField int Quantity, count
FieldType.toggle RjToggleField bool Accept terms, enable feature
FieldType.radio RjRadioField String (option id) Gender, single choice
FieldType.chip RjChipField List<String> (option ids) Tags, interests, skills
FieldType.custom Your widget Any Signature pad, star rating, maps

Common Patterns

Pre-filling Values (Edit Mode)

RjForm(
  fields: fields,
  initialValues: {
    'name': 'John Doe',
    'email': 'john@example.com',
    'country': 'bd',
    'dob': DateTime(1990, 5, 15),
  },
  onSubmit: (_) async {},
)

External Controller with Custom Submit Button

class MyForm extends StatefulWidget {
  const MyForm({super.key});

  @override
  State<MyForm> createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  final _controller = FormController();

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  Future<void> _submit() async {
    if (_controller.validate(fields)) {
      final result = _controller.toResult();
      // handle result
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Expanded(
          child: RjForm(
            fields: fields,
            controller: _controller,
            hideSubmitButton: true,
            onSubmit: (_) async {},
          ),
        ),
        ElevatedButton(
          onPressed: _submit,
          child: const Text('Submit'),
        ),
      ],
    );
  }
}

View Mode (Read-only)

RjForm(
  fields: fields,
  initialValues: existingRecord,
  viewOnly: true,
  onSubmit: (_) async {}, // Never called in view mode
)

Real-time Change Tracking

RjForm(
  fields: fields,
  onSubmit: (_) async {},
  onChanged: (key, value) {
    // Useful for auto-save, analytics, or enabling buttons
    print('$key changed to: $value');
  },
)

Error Summary

RjForm(
  fields: fields,
  onSubmit: (_) async {},
  showErrorsSummary: true,
  // Optional: customize the summary message
  errorsSummaryBuilder: (errors) {
    return 'Please fix ${errors.length} error(s) before submitting.';
  },
)

Theming

RjForm(
  fields: fields,
  theme: RjFormTheme(
    primaryColor:    const Color(0xFF0D9488),
    borderColor:     const Color(0xFFD1D5DB),
    errorColor:      const Color(0xFFDC2626),
    borderRadius:    BorderRadius.circular(12),
    fieldSpacing:    24,
    fieldFillColor:  Colors.grey.shade50,
    labelStyle:      const TextStyle(fontWeight: FontWeight.w600),
    submitButtonColor: const Color(0xFF0D9488),
  ),
  onSubmit: (_) async {},
)

Best Practices

  1. Always provide explicit key values. Keys are used as identifiers for form state. Duplicate keys cause silent data overwrites.

  2. Combine required: true with validators. Validators skip empty values by design. Use required to enforce presence, then validators to enforce format.

  3. Use typed FieldConfig over flat params. SliderConfig, DateConfig, ImageConfig, etc., are the preferred way to configure field-specific behavior. Flat params (sliderMin, dateFormat, etc.) are kept for backward compatibility.

  4. Dispose external controllers. If you create a FormController yourself, call dispose() in your widget's dispose() method. Controllers managed internally by RjForm are disposed automatically.

  5. Use DropdownSource.async for large lists. Static dropdowns load all items at widget build. For lists fetched from an API or database, use DropdownSource.async to avoid blocking the UI thread.

  6. Provide unique keys for sections. FieldMeta.section requires an explicit key parameter. Duplicate section keys will trigger an assertion in debug mode.

  7. Handle type casting in FormResult.get<T>(). Values are stored with their native types (DateTime, double, List<String>, etc.). If you cast to the wrong type, get<T>() returns null. Check the Field Types table for expected return types.

Examples & Demo

A minimal working example is included in the /example folder for quick testing.

For a full-featured demo application with multiple screens and advanced use cases, check:

👉 https://github.com/ReturajProshad/rj_form_engine_demo

Run minimal example

git clone https://github.com/ReturajProshad/rj_form_engine
cd rj_form_engine/example
flutter pub get
flutter run

Limitations

  • Image picker supports gallery only. Camera capture is not currently supported. For camera or file picker functionality, use a custom field via FieldMeta.custom.
  • No built-in form state persistence. Form data is lost if the app is killed in the background. Implement your own persistence layer if needed.
  • Single-column layout. Fields render vertically. Multi-column or grid layouts require custom field builders.
  • No i18n built-in. Labels, hints, and error messages are plain strings. You must handle localization yourself (e.g., via AppLocalizations.of(context)).
  • FormResult.get<T>() returns null on type mismatch. If you request result.get<int>('age') but the stored value is a String, you get null silently. Always use the correct type.

Roadmap

  • Camera support for image fields
  • Multi-column / grid layout support
  • Built-in i18n / localization
  • Form state persistence (auto-save / restore)
  • File upload field (non-image)
  • Rich text / markdown field
  • Dynamic field addition/removal at runtime
  • Integration tests

Contributing

Contributions are welcome! If you find a bug or have a feature request:

  1. Open an issue with a clear description and reproduction steps.
  2. For code contributions, please fork the repo, create a feature branch, and submit a pull request.
  3. Follow the existing code style and include tests for new functionality.

Author

Returaj Proshad Shornocar — Flutter & Mobile Software Engineer

GitHub · LinkedIn

License

MIT — see LICENSE

Libraries

rj_form_engine
rj_form_engine — A schema-driven form engine for Flutter.