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wc form validators

Form Validators #
A Flutter plugin which provides a set of validators that can be used by form fields.

About #
This flutter plugin provides utility functions to make form validation easy. This plugin was inspired by Angular Validators class.
Version #
This plugin supports dart version 2.2+
How to use Form Validators #
For Example: #
Validating if TextFormField is non-empty and has a valid email address
TextFormField(
decoration: InputDecoration(
labelText: 'Email',
),
validator: Validators.compose([
Validators.required('Email is required'),
Validators.email('Invalid email address'),
]),
),
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Api Overview #
Utility Functions #

Required
Minimum
Maximum
Email
Minimum Length
Maximum Length
Pattern
Compose

All validator functions have return type of FormFieldValidator<String> which is a required type for validator field in TextFormField.

Required #
Validators.required(String errorMessage) is validator that requires the field have a non-empty value.
Example
This code will validate the name and show error if it is empty.
TextFormField(
decoration: InputDecoration(
labelText: 'Name',
),
validator: Validators.required('Name is required'),
),
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Parameters

Params
Description

errorMessage
String value is passed to this parameter to show an error in case of a validation failure.

Minimum #
Validators.min(double min, String errorMessage) is a validator that requires the field's value be greater than or equal to the provided number (double min). TextFormField's value must be an integer or double otherwise this validator will throw a parse exception.
Example
This code will validate a TextFormField's value and show an error in case its value is non-empty and less than 5.
TextFormField(
keyboardType: TextInputType.numberWithOptions(
decimal: true,
signed: true,
),
decoration: InputDecoration(
labelText: 'Minimum 5',
),
validator: Validators.min(5, 'Value less than 5 not allowed'),
),

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Parameters
Validators.min takes two parameters.

Params
Description

min
double value is passed to this param. Validator will return an error if TextFormField is non-empty and its value is less than min

errorMessage
String value is passed to this parameter to show an error in case of a validation failure

Maximum #
Validators.max(double max, String errorMessage) is a validator that requires the field's value to be less than or equal to the provided number (double max). TextFormField's value must be an integer or double otherwise this validator will throw a parse exception.
Example
This code will validate TextFormField's value and show an error in case its value is non-empty and greater than 5.
TextFormField(
keyboardType: TextInputType.numberWithOptions(
decimal: true,
signed: true,
),
decoration: InputDecoration(
labelText: 'Maximum 5',
),
validator: Validators.max(5, 'Value greater than 5 not allowed'),
),

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Parameters
Validators.max takes two parameters.

Params
Description

max
double value is passed to this param. Validator will return an error if TextFormField is non-empty and its value is greater than max

errorMessage
String value is passed to this parameter to show an error in case of validation failure

Email #
Validators.email(String errorMessage) is a validator that requires the field's value pass an email validation test.
Its uses regex of HTML5 for email validation.
Its regex is ^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,253}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,253}[a-zA-Z0-9])?)*$
If you want to use custom regex for email validation, please take a look at Pattern.
Example
This code will validate the email and show an error if TextFormField's value is non-empty and the email address is invalid.
TextFormField(
decoration: InputDecoration(
labelText: 'Email',
),
validator: Validators.email('Invalid email address'),
),
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Parameters

Params
Description

errorMessage
String value is passed to this parameter to show an error in case of validation failure.

Minimum Length #
Validators.minLength(int minLength, String errorMessage) is a validator that requires the length of the field's value to be greater than or equal to the provided minimum length.
Example
This code will validate the TextFormField's value and show an error in case field's value is non-empty and its character length is less than 5.
TextFormField(
decoration: InputDecoration(
labelText: 'Minimum length 5',
),
validator: Validators.minLength(5, 'Characters are less than 5'),
),
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Parameters

Params
Description

minLength
int value is passed to this param. Validator will return an error if TextFormField is non-empty and its number of characters is less than minLength.

errorMessage
String value is passed to this parameter to show error in case of validation failure.

Maximum Length #
Validators.maxLength(int maxLength, String errorMessage) is a validator that requires the length of the field's value to be less than or equal to the provided maximum length.
Example
This code will validate TextFormField's value and show an error in case the field's value is non-empty and its character length is greater than 5.
TextFormField(
decoration: InputDecoration(
labelText: 'Maximum length 5',
),
validator: Validators.maxLength(5, 'Characters are greater than 5'),
),
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Parameters

Params
Description

maxLength
int value is passed to this param. The validator will return an error if the TextFormField is non-empty and its number of characters are greater than maxLength.

errorMessage
String value is passed to this parameter to show error in case of validation failure.

Pattern #
Validators.patternString(String pattern, String errorMessage) and Validators.patternRegExp(RegExp pattern, String errorMessage) are validators that require the field's value to match a regex pattern.
In case of Validators.patternString, you need to pass regex like this r"^[A-Za-z]+$"
Examples
This code will validate the TextFormField's value and show an error in case the field's value is non-empty and it contains characters other than letters.
patternRegExp
TextFormField(
decoration: InputDecoration(
labelText: 'Pattern r"^[A-Za-z]+\$"',
),
validator: Validators.patternRegExp(
RegExp(r"^[A-Za-z]+$"), 'Only alphabets are allowed'),
),

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patternString
TextFormField(
decoration: InputDecoration(
labelText: 'Pattern r"^[A-Za-z]+\$"',
),
validator: Validators.patternString(
r"^[A-Za-z]+$", 'Only alphabets are allowed'),
),
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Parameters

Params
Description

pattern
String or RegExp the value is passed to this param. The validator will return an error if the TextFormField is non-empty and it's not matching the pattern that you have provided.

errorMessage
String value is passed to this parameter to show error in case of a validation failure.

Compose #
Validators.compose(List<FormFieldValidator<String>> validators) composes multiple validators into a single validator.
How it works
This function takes multiple validators as a list and will validate each validator in the provided sequence. If any of its validator returns an error message, it won't check the remaining validators and will return this error to the TextFormField.
Example
This code will validate that Name is non-empty and has a character length between 5 and 10.
TextFormField(
decoration: InputDecoration(
labelText: 'Name',
),
validator: Validators.compose([
Validators.required('Name is required'),
Validators.minLength(5, 'Name cannot be less than 5 characters'),
Validators.maxLength(10, 'Name cannot be greater than 10 characters'),
]),
),
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Parameters

Params
Description

validators
List<FormFieldValidator<String>> value is passed to this param containing validators that you want to combine into one validator

Note:

If TextFormField's value is empty, then validators Minimum, Maximum, Email, Minimum Length, Maximum Length and Pattern won't return any error because it considers TextFormField as optional. Use these validators in combination with the Required validator if the specified TextFormField is compulsory and you want a validation failure if the field is empty. Check Compose validator to find out how to merge multiple validators.