form_validation 2.1.0+11 icon indicating copy to clipboard operation
form_validation: ^2.1.0+11 copied to clipboard

Validators that can be used directly via code or constructed from JSON to provide dynamic validation.

Table of Contents

form_validation #

Form validators that can be used directly via code or constructed from JSON to provide more dynamic validation.

Live Web Example

Using the library #

Add the repo to your Flutter pubspec.yaml file.

  form_validation: <<version>> 

Then run...

flutter packages get

Validators #

The library provides a set of built-in validators while also providing a mechanism for applications to provide their own validators. All the built-in validators are able to be deserialized via JSON. They all expect an attribute of type to match a specific value when being desearialized.

Note: With the sole exception of RequiredValidator, all built in validators will pass on null or empty values.

CurrencyValidatorcurrencyEnsures the value is a valid currency
EmailValidatoremailEnsures the value is a validly formatted email address
MaxLengthValidatormax_lengthEnsures the value contains no more than a set number of characters
MaxNumberValidatormax_numberEnsures the value is no larger than a given number
MinLengthValidatormin_lengthEnsures the value contains no fewer than a set number of characters
MinNumberValidatormin_numberEnsures the value is no smaller than a given number
NumberValidatornumberEnsures the value is a valid number
PhoneNumberValidatorphone_numberEnsures the value is a validly formatted phone number
RequiredValidatorrequiredEnsures the value is not null, empty, nor white space only

Validation Messages / Translations #

The library provides a default set of English error messages for each validator's error message. This library uses the static_translations library for the string and language management, see it for details on how to override the defaults or provide values for other languages.

form_validation_currencylabelUsed when an invalid currency value is detected
form_validation_currency_positivelabelUsed when a valid, but negative, currency value is detected
form_validation_emaillabelUsed when an invalid email is detected
form_validation_max_lengthlabel, lengthUsed when a value contains more characters than length
form_validation_max_numberlabel, numberUsed when a value is larger than number
form_validation_min_lengthlabel, lengthUsed when a value contains fewer characters than length
form_validation_min_numberlabel, numberUsed when a value is smaller than number
form_validation_numberlabelUsed when a number is expected but not detected
form_validation_number_decimallabelUsed when a number is detected, but not allowed to be a decimal
form_validation_phone_numberlabelUsed when an invalid phone number is detected
form_validation_requiredlabelUsed when a value is required, but detected as null, empty, or all white space

JSON Support #

The Validator class can be used to decode a list of child ValueValidator entries. Each of the built-in validators can be deserialized via JSON. In addition to being able to deserialize from JSON, each of the built-in validators supports serializing to a JSON compatible map via toJson or an actual JSON encoded string via toJsonString.

The overall struction needs to be:

  "validators": [
    // One or more of the JSON objects shown below

CurrencyValidator #

  "allowNegative": <bool>, // Default: true; states whether negative values are allowed or not
  "type": "currency"

EmailValidator #

  "type": "email"

MaxLengthValidator #

  "length": <int>, // The maximum length the value may be
  "type": "max_length"

MaxNumberValidator #

  "length": <int>, // The maximum number the value may be
  "type": "max_number"

MinLengthValidator #

  "length": <int>, // The minimum length the value may be
  "type": "min_length"

MinNumberValidator #

  "length": <int>, // The minimum number the value may be
  "type": "min_number"

NumberValidator #

  "type": "number"

PhoneNumberValidator #

  "type": "phone_number"

RequiredValidator #

  "type": "required"

Custom Validators #

The Validator supports custom validators being added either directly through classes extending the ValueValidator abstract class and passing them in via the constructor. Alternatively, an application may register a validator type with Validator using the registerCustomValidatorBuilder function.

Example #

class MyCustomValidator extends ValueValidator {
  static const type = 'my_custom_validator';

  static MyCustomValidator fromDynamic(dynamic map) {
      // initialization args go here

    MyCustomValidator result;

    if (map != null) {
      assert(map['type'] == type);

      result = MyCustomValidator(
        // Do additional JSON conversion here

    return result;

  Map<String, dynamic> toJson() => {
    // add additional attributes here
    "type": type,

  String validate({
    @required BuildContext context,
    @required String label,
    @required String value,
  }) {
    String error;

    // In general, validators should pass if the value is empty.  Combine 
    // validators with the RequiredValidator to ensure a value is non-empty.
    if (value?.isNotEmpty == true) {
      // Do processing to determine if the value is valid or not

    return error;


void main() {

  // start app


var jsonStr = '''
  "validators": [{
    "type": "required"
  }, {
    "type": "my_custom_validator"

// This will create a validation chain with the RequiredValidator as well as the
// MyCustomValidator defined above
var validator = Validator.fromDynamic(json.decode(jsonStr));
pub points


verified publisher

Validators that can be used directly via code or constructed from JSON to provide dynamic validation.



API reference


Icon for licenses.MIT (LICENSE)


flutter, intl, json_class, meta, static_translations


Packages that depend on form_validation