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Flutter FormBuilder - flutter_form_builder

This package helps in creation of data collection forms in Flutter by removing the boilerplate needed to build a form, validate fields, react to changes, and collect final user input.

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Simple Usage

To use this plugin, add flutter_form_builder as a dependency in your pubspec.yaml file.

Flutter Version Guide

  • Flutter 1.20 => v4.*
  • Flutter 2.* with no null-safety => v5.*
  • Flutter 2.* null-safety => v6.* - some dependencies (and therefore fields)* were removed to achieve null safety

New Video Tutorial

Youtube Video Tutorial
Check out the video tutorial from SyntacOps on Youtube

Example

final _formKey = GlobalKey<FormBuilderState>();

@override
Widget build(BuildContext context) {
  return Column(
    children: <Widget>[
      FormBuilder(
        key: _formKey,
        autovalidate: true,
        child: Column(
          children: <Widget>[
            FormBuilderFilterChip(
              name: 'filter_chip',
              decoration: InputDecoration(
                labelText: 'Select many options',
              ),
              options: [
                FormBuilderFieldOption(
                    value: 'Test', child: Text('Test')),
                FormBuilderFieldOption(
                    value: 'Test 1', child: Text('Test 1')),
                FormBuilderFieldOption(
                    value: 'Test 2', child: Text('Test 2')),
                FormBuilderFieldOption(
                    value: 'Test 3', child: Text('Test 3')),
                FormBuilderFieldOption(
                    value: 'Test 4', child: Text('Test 4')),
              ],
            ),
            FormBuilderChoiceChip(
              name: 'choice_chip',
              decoration: InputDecoration(
                labelText: 'Select an option',
              ),
              options: [
                FormBuilderFieldOption(
                    value: 'Test', child: Text('Test')),
                FormBuilderFieldOption(
                    value: 'Test 1', child: Text('Test 1')),
                FormBuilderFieldOption(
                    value: 'Test 2', child: Text('Test 2')),
                FormBuilderFieldOption(
                    value: 'Test 3', child: Text('Test 3')),
                FormBuilderFieldOption(
                    value: 'Test 4', child: Text('Test 4')),
              ],
            ),
            FormBuilderDateTimePicker(
              name: 'date',
              // onChanged: _onChanged,
              inputType: InputType.time,
              decoration: InputDecoration(
                labelText: 'Appointment Time',
              ),
              initialTime: TimeOfDay(hour: 8, minute: 0),
              // initialValue: DateTime.now(),
              // enabled: true,
            ),
            FormBuilderDateRangePicker(
              name: 'date_range',
              firstDate: DateTime(1970),
              lastDate: DateTime(2030),
              format: DateFormat('yyyy-MM-dd'),
              onChanged: _onChanged,
              decoration: InputDecoration(
                labelText: 'Date Range',
                helperText: 'Helper text',
                hintText: 'Hint text',
              ),
            ),
            FormBuilderSlider(
              name: 'slider',
              validator: FormBuilderValidators.compose([
                FormBuilderValidators.min(context, 6),
              ]),
              onChanged: _onChanged,
              min: 0.0,
              max: 10.0,
              initialValue: 7.0,
              divisions: 20,
              activeColor: Colors.red,
              inactiveColor: Colors.pink[100],
              decoration: InputDecoration(
                labelText: 'Number of things',
              ),
            ),
            FormBuilderCheckbox(
              name: 'accept_terms',
              initialValue: false,
              onChanged: _onChanged,
              title: RichText(
                text: TextSpan(
                  children: [
                    TextSpan(
                      text: 'I have read and agree to the ',
                      style: TextStyle(color: Colors.black),
                    ),
                    TextSpan(
                      text: 'Terms and Conditions',
                      style: TextStyle(color: Colors.blue),
                    ),
                  ],
                ),
              ),
              validator: FormBuilderValidators.equal(
                context,
                true,
                errorText:
                    'You must accept terms and conditions to continue',
              ),
            ),
            FormBuilderTextField(
              name: 'age',
              decoration: InputDecoration(
                labelText:
                    'This value is passed along to the [Text.maxLines] attribute of the [Text] widget used to display the hint text.',
              ),
              onChanged: _onChanged,
              // valueTransformer: (text) => num.tryParse(text),
              validator: FormBuilderValidators.compose([
                FormBuilderValidators.required(context),
                FormBuilderValidators.numeric(context),
                FormBuilderValidators.max(context, 70),
              ]),
              keyboardType: TextInputType.number,
            ),
            FormBuilderDropdown(
              name: 'gender',
              decoration: InputDecoration(
                labelText: 'Gender',
              ),
              // initialValue: 'Male',
              allowClear: true,
              hint: Text('Select Gender'),
              validator: FormBuilderValidators.compose(
                  [FormBuilderValidators.required(context)]),
              items: genderOptions
                  .map((gender) => DropdownMenuItem(
                        value: gender,
                        child: Text('$gender'),
                      ))
                  .toList(),
            ),
          ],
        ),
      ),
      Row(
        children: <Widget>[
          Expanded(
            child: MaterialButton(
              color: Theme.of(context).accentColor,
              child: Text(
                "Submit",
                style: TextStyle(color: Colors.white),
              ),
              onPressed: () {
                _formKey.currentState.save();
                if (_formKey.currentState.validate()) {
                  print(_formKey.currentState.value);
                } else {
                  print("validation failed");
                }
              },
            ),
          ),
          SizedBox(width: 20),
          Expanded(
            child: MaterialButton(
              color: Theme.of(context).accentColor,
              child: Text(
                "Reset",
                style: TextStyle(color: Colors.white),
              ),
              onPressed: () {
                _formKey.currentState.reset();
              },
            ),
          ),
        ],
      )
    ],
  );
}

l10n

Just add the FormBuilderLocalizations.delegate in the list of your app's localizationsDelegates

  return MaterialApp(
      supportedLocales: [
        Locale('en'),
        Locale('it'),
        Locale('fr'),
        Locale('es'),
      ],
      localizationsDelegates: [
        FormBuilderLocalizations.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],

Input widgets

The currently supported fields include:

  • FormBuilderCheckbox - Single Checkbox field
  • FormBuilderCheckboxGroup - List of Checkboxes for multiple selection
  • FormBuilderChoiceChip - Creates a chip that acts like a radio button.
  • FormBuilderDateRangePicker - For selection of a range of dates
  • FormBuilderDateTimePicker - For Date, Time and DateTime input
  • FormBuilderDropdown - Used to select one value from a list as a Dropdown
  • FormBuilderFilterChip - Creates a chip that acts like a checkbox.
  • FormBuilderRadioGroup - Used to select one value from a list of Radio Widgets
  • FormBuilderRangeSlider - Used to select a range from a range of values
  • FormBuilderSegmentedControl - For selection of a value from the CupertinoSegmentedControl as an input
  • FormBuilderSlider - For selection of a numerical value on a slider
  • FormBuilderSwitch - On/Off switch field
  • FormBuilderTextField - A Material Design text field input.

In order to create an input field in the form, along with the label, and any applicable validation, there are several attributes that are supported by all types of inputs namely:

Attribute Type Default Required Description
name String Yes This will form the key in the form value Map
initialValue T null No The initial value of the input field
enabled bool true No Determines whether the field widget will accept user input.
decoration InputDecoration InputDecoration() No Defines the border, labels, icons, and styles used to decorate the field.
validator FormFieldValidator<T> null No A FormFieldValidator that will check the validity of value in the FormField
onChanged ValueChanged<T> null No This event function will fire immediately the the field value changes
valueTransformer ValueTransformer<T> null No Function that transforms field value before saving to form value. e.g. transform TextField value for numeric field from String to num
The rest of the attributes will be determined by the type of Widget being used.

Additional input fields

To make this package compartible with as many platforms as Flutter supports, we separated some input fields into their own packages because they depend on platform-specific plugins. Here's are the links to some of the packages that could be used with FormBuilder

Building your own custom field

To build your own field within a FormBuilder, we use FormBuilderField which will require that you define your own field.

var options = ["Option 1", "Option 2", "Option 3"];
FormBuilderField(
  name: "name",
  validator: FormBuilderValidators.compose([
    FormBuilderValidators.required(context),
  ]),
  builder: (FormFieldState<dynamic> field) {
    return InputDecorator(
      decoration: InputDecoration(
        labelText: "Select option",
        contentPadding:
            EdgeInsets.only(top: 10.0, bottom: 0.0),
        border: InputBorder.none,
        errorText: field.errorText,
      ),
      child: Container(
        height: 200,
        child: CupertinoPicker(
          itemExtent: 30,
          children: options.map((c) => Text(c)).toList(),
          onSelectedItemChanged: (index) {
            field.didChange(options[index]);
          },
        ),
      ),
    );
  },
),

Programmatically changing field value

You can either change the value of one field at a time like so:

_formKey.currentState.fields['color_picker'].didChange(Colors.black);

Or multiple fields value like so:

_formKey.currentState.patchValue({
  'age': '50',
  'slider': 6.7,
  'filter_chip': ['Test 1'],
  'choice_chip': 'Test 2',
  'rate': 4,
  'chips_test': [
    Contact('Andrew', '[email protected]', 'https://d2gg9evh47fn9z.cloudfront.net/800px_COLOURBOX4057996.jpg'),
  ],
});

Validation

The validator attribute in fields take in a FormFieldValidator which checks the validity of the field. A FormFieldValidator returns null if validation is successful and a String for the errorText if validation fails.

Built-in Validators

This package comes with several most common FormFieldValidators such as required, numeric, mail, URL, min, max, minLength, maxLength, IP, credit card etc. with default errorText.

Available built-in validators include:

  • FormBuilderValidators.creditCard() - requires the field's value to be a valid credit card number.
  • FormBuilderValidators.date() - requires the field's value to be a valid date string.
  • FormBuilderValidators.email() - requires the field's value to be a valid email address.
  • FormBuilderValidators.equal() - requires the field's value be equal to provided object.
  • FormBuilderValidators.integer() - requires the field's value to be an integer.
  • FormBuilderValidators.ip() - requires the field's value to be a valid IP address.
  • FormBuilderValidators.match() - requires the field's value to match the provided regex pattern.
  • FormBuilderValidators.max() - requires the field's value to be less than or equal to the provided number.
  • FormBuilderValidators.maxLength() - requires the length of the field's value to be less than or equal to the provided maximum length.
  • FormBuilderValidators.min() - requires the field's value to be greater than or equal to the provided number.
  • FormBuilderValidators.minLength() - requires the length of the field's value to be greater than or equal to the provided minimum length.
  • FormBuilderValidators.numeric() - requires the field's value to be a valid number.
  • FormBuilderValidators.required() - requires the field have a non-empty value.
  • FormBuilderValidators.url() - requires the field's value to be a valid url.

Using multiple validators

FormBuilderValidators class comes with a very useful static function named compose() which takes any number of FormFieldValidator functions. On validation each validator is run and if any returns a non-null value (i.e. a String), validation fails and the errorText for the field is set as the returned string.

Validation example:

FormBuilderTextField(
  name: 'age',
  decoration: InputDecoration(labelText: 'Age'),
  validator: FormBuilderValidators.compose([
    FormBuilderValidators.numeric(context, errorText: 'La edad debe ser numérica.'),
    FormBuilderValidators.max(context, 70),
    (val){
      if(val < 0)
        return 'We cannot have a negative age';
      return null;
    }
  ]),
),

Programmatically inducing an error

Option 1 - Using FormBuilder / FieldBuilderField key

final _formKey = GlobalKey<FormBuilderState>();
final _emailFieldKey = GlobalKey<FormBuilderFieldState>();
...
FormBuilder(
  key: _formKey,
  child: Column(
    children: [
      FormBuilderTextField(
        key: _emailFieldKey
        name: 'email',
        decoration: InputDecoration(labelText: 'Email'),
        validator: FormBuilderValidators.compose([
          FormBuilderValidators.required(context),
          FormBuilderValidators.email(context),
        ]),
      ),
      RaisedButton(
        child: Text('Submit'),
        onPressed: () async {
          if(await checkIfEmailExists()){
            // Either invalidate using Form Key
            _formKey.currentState?.invalidateField(name: 'email', errorText: 'Email already taken.');
            // OR invalidate using Field Key
            _emailFieldKey.currentState?.invalidate('Email already taken.');
          }
        },
      ),
    ],
  ),
),

Option 2 - Using InputDecoration.errorText

Declare a variable to hold your error:

String _emailError;

Use the variable as the errorText within InputDecoration

FormBuilderTextField(
  name: 'email',
  decoration: InputDecoration(
    labelText: 'Email',
    errorText: _emailError,
  ),
  validator: FormBuilderValidators.compose([
      FormBuilderValidators.required(context),
      FormBuilderValidators.email(context),
  ]),
),

Set the error text

RaisedButton(
  child: Text('Submit'),
  onPressed: () async {
    setState(() => _emailError = null);
    if(await checkIfEmailExists()){
      setState(() => _emailError = 'Email already taken.');
    }
  },
),

Conditional validation

You can also validate a field based on the value of another field

FormBuilderRadioGroup(
  decoration: InputDecoration(labelText: 'My best language'),
  name: 'my_language',
  validator: FormBuilderValidators.required(context),
  options: [
    'Dart',
    'Kotlin',
    'Java',
    'Swift',
    'Objective-C',
    'Other'
  ]
    .map((lang) => FormBuilderFieldOption(value: lang))
    .toList(growable: false),
  ),
  FormBuilderTextField(
    name: 'specify',
    decoration:
        InputDecoration(labelText: 'If Other, please specify'),
    validator: (val) {
      if (_formKey.currentState.fields['my_language']?.value ==
              'Other' &&
          (val == null || val.isEmpty)) {
        return 'Kindly specify your language';
      }
      return null;
    },
  ),

SUPPORT

Issues and PRs

Any kind of support in the form of reporting bugs, answering questions or PRs is always appreciated.

We especially welcome efforts to internationalize/localize the package by translating the default validation errorText strings.

Localizing messages

  1. With the app’s root directory as the current directory, generate l10n/intl_messages.arb from lib/localization/form_builder_localizations.dart:

    flutter pub pub run intl_translation:extract_to_arb --output-dir=lib/l10n lib/localization/form_builder_localizations.dart

  2. The intl_messages.arb file is a JSON format map with one entry for each Intl.message() function defined in lib/localization/form_builder_localizations.dart. This file serves as a template for the different translations (for example intl_en.arb and intl_es.arb are English and Spanish translations respectively). You are therefore you are required to copy the intl_messages.arb and put the content in a new file with the name of your locale with a name with format intl_<locale>.arb (e.g. intl_fr.arb for French Translations).

  3. Translate the messages in the new file to the required language.

  4. With the app’s root directory as the current directory, generate intl_messages_<locale>.dart for your intl_<locale>.arb file and update intl_messages_all.dart, which imports all of the messages files:

flutter pub run intl_translation:generate_from_arb --output-dir=lib/l10n --no-use-deferred-loading lib/localization/form_builder_localizations.dart lib/l10n/intl_<en>.arb lib/l10n/intl_messages.arb

e.g. To generate for French run: flutter pub run intl_translation:generate_from_arb --output-dir=lib/l10n --no-use-deferred-loading lib/localization/form_builder_localizations.dart lib/l10n/intl_fr.arb lib/l10n/intl_messages.arb

  • Alternatively you could run the following command to generate Dart translation files for all the intl_<locale>.arb files in the l10n/ directory:

flutter pub pub run intl_translation:generate_from_arb --output-dir=lib/l10n --no-use-deferred-loading lib/localization/form_builder_localizations.dart lib/l10n/intl_*.arb

  1. Include your new language to FormBuilderLocalization's supported languages. Go to lib/localization/form_builder_localizations.dart and include the language like so:

@override
  bool isSupported(Locale locale) {
    return ['en', 'es', 'fr'].contains(locale.languageCode);
  }
  1. Submit your PR and be of help to millions of people all over the world!

Coffee :-)

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