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Description:

form validation

Table of Contents

form_validation

Using the library
Validators
Validation Messages / Translations
JSON Support

CurrencyValidator
EmailValidator
MaxLengthValidator
MaxNumberValidator
MinLengthValidator
MinNumberValidator
NumberValidator
PhoneNumberValidator
RequiredValidator

Custom Validators

Example

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.
dependencies:
form_validation: <<version>>
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Then run...
flutter packages get
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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.

Class
Type
Description

CurrencyValidator
currency
Ensures the value is a valid currency

EmailValidator
email
Ensures the value is a validly formatted email address

MaxLengthValidator
max_length
Ensures the value contains no more than a set number of characters

MaxNumberValidator
max_number
Ensures the value is no larger than a given number

MinLengthValidator
min_length
Ensures the value contains no fewer than a set number of characters

MinNumberValidator
min_number
Ensures the value is no smaller than a given number

NumberValidator
number
Ensures the value is a valid number

PhoneNumberValidator
phone_number
Ensures the value is a validly formatted phone number

RequiredValidator
required
Ensures 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 provides a class named [FormValidationTranslations] that has a values map. In it is the default strings to use. Update that map when a different language should be used. Below are the available keys.

Key
Parameters
Description

form_validation_currency
label
Used when an invalid currency value is detected

form_validation_currency_positive
label
Used when a valid, but negative, currency value is detected

form_validation_email
label
Used when an invalid email is detected

form_validation_max_length
label, length
Used when a value contains more characters than length

form_validation_max_number
label, number
Used when a value is larger than number

form_validation_min_length
label, length
Used when a value contains fewer characters than length

form_validation_min_number
label, number
Used when a value is smaller than number

form_validation_number
label
Used when a number is expected but not detected

form_validation_number_decimal
label
Used when a number is detected, but not allowed to be a decimal

form_validation_phone_number
label
Used when an invalid phone number is detected

form_validation_required
label
Used 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
]
}
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CurrencyValidator #
{
"allowNegative": <bool>, // Default: true; states whether negative values are allowed or not
"type": "currency"
}
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EmailValidator #
{
"type": "email"
}
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MaxLengthValidator #
{
"length": <int>, // The maximum length the value may be
"type": "max_length"
}
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MaxNumberValidator #
{
"length": <int>, // The maximum number the value may be
"type": "max_number"
}
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MinLengthValidator #
{
"length": <int>, // The minimum length the value may be
"type": "min_length"
}
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MinNumberValidator #
{
"length": <int>, // The minimum number the value may be
"type": "min_number"
}
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NumberValidator #
{
"type": "number"
}
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PhoneNumberValidator #
{
"type": "phone_number"
}
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RequiredValidator #
{
"type": "required"
}
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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) {
MyCustomValidator({
// 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() {
Validator.registerCustomValidatorBuilder(
MyCustomValidator.type,
MyCustomValidator.fromDynamic,
);

// 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));
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