wc_form_validators 0.1.0

A Flutter plugin to validate forms with util functions.

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 is inspiration from 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 valid email address

TextFormField(
  decoration: InputDecoration(
    labelText: 'Email',
  ),
  validator: Validators.compose([
    Validators.required('Email is required'),
    Validators.email('Invalid email address'),
  ]),
),

Api Overview

Utility Functions

• Required
• Minimum
• Maximum
• Email
• Minimum Length
• Maximum Length
• Pattern
• Compose

All validator functions have have return type of FormFieldValidator<String> which is 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 if name and show error if it is empty.

TextFormField(
  decoration: InputDecoration(
    labelText: 'Name',
  ),
  validator: Validators.required('Name is required'),
),

Parameters

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

---

Minimum

Validators.min(double min, String errorMessage) is a validator that requires the field's value to be greater than or equal to the provided number (double min). TextFormField's value must be integer or double otherwise this validator will throw parse exception.

Example

This code will validate 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'),
  ),

Parameters

Validators.min takes two parameters.

Params	Description
min	double value is passed to this param. Validator will return error if TextFormField is non-empty and its value is less than min
errorMessage	String value is passed to this parameter to show error in case of 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 integer or double otherwise this validator will throw parse exception.

Example

This code will validate TextFormField's value and show 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'),
  ),

Parameters

Validators.max takes two parameters.

Params	Description
max	double value is passed to this param. Validator will return error if TextFormField is non-empty and its value is greater than max
errorMessage	String value is passed to this parameter to show 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 email and show error if TextFormField's value is non-empty and email address is invalid.

  TextFormField(
    decoration: InputDecoration(
      labelText: 'Email',
    ),
    validator: Validators.email('Invalid email address'),
  ),

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 TextFormField's value and show error in case of field's value is non-empty and its character's length is less than 5.

  TextFormField(
    decoration: InputDecoration(
      labelText: 'Minimum length 5',
    ),
    validator: Validators.minLength(5, 'Characters are less than 5'),
  ),

Parameters

Params	Description
minLength	int value is passed to this param. Validator will return error if TextFormField is non-empty and its number of characters are 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 error in case of field's value is non-empty and its character's length is greater than 5.

  TextFormField(
    decoration: InputDecoration(
      labelText: 'Maximum length 5',
    ),
    validator: Validators.maxLength(5, 'Characters are greater than 5'),
  ),

Parameters

Params	Description
maxLength	int value is passed to this param. Validator will return error if 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 requires 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 TextFormField's value and show error in case of field's value is non-empty and its contains character other than alphabets.

patternRegExp

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

patternString

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

Parameters

Params	Description
pattern	String or RegExp value is passed to this param. Validator will return error if TextFormField is non-empty and its not matching pattern that you have provided.
errorMessage	String value is passed to this parameter to show error in case of 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 list and will validate each validator in provided sequence. If any of its validator returns error message, it won't check remaining validators and will return this error to TextFormField.

Example

This code will validate that Name is non-empty and has 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'),
    ]),
  ),

Parameters

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

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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 with combination of Required validator if specified TextFormField is compulsory and want validation failure if field is empty. Check Compose validator to find out how to merge multiple validators.

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