Flrx Validator

Validator

Introduction

Flrx Validator allows you to take a specific value and validate against a set of rules. It is primarily designed to be used by Flutter's FormField's validator, however you can use it with any Dart 2 Project.

The Validator takes a List of Rule. The value supplied to the Validator is supplied to the Rules in the order they were registered. The error message of the first Rule that fails is returned back. If all the Rules pass, then null is returned to the FormField.

Running the Validator

There are two ways to run the validator.

Through the instance

The Validator instance itself can be passed to a FormField Widget if you want to add validation.

TextFormField(validator: Validator<String>())

Via validate()

The Validator's validate() method is useful if you want to validate a value outside a FormField. For example, Flutter does not have any Cupertino FormField Widgets. For such cases you can perform validation like this:


  @override
  Widget build(BuildContext context) {
  
    ...  
        CupertinoTextField(controller: _textEditingController),
        Text(emailValidationMessage),
    ...
  
  }
      
  void onFormSubmitPressed() {
    String value = _textEditingController.text;
    setState(() {
      emailValidationMessage = Validator<String>().validate(value) ?? '';
      });
  }
  
  ...

}

You can see the full example here.

Although for simple forms this may seem like a good idea, this could quickly go out of hand. You might want to use a Custom FormField Widget instead.

Adding Rules

The Validator takes Rules against which the value is validated. You can add Rules to the validator in the following ways

Via Validator() constructor

TextFormField(validator: Validator<String>(rules: [RequiredRule()]))

As Validator's add method returns Validator instance, therefore we can chain it to do something like this.

Via add()

TextFormField(
    validator: Validator<String>()
        .add(RequiredRule())
)

As Validator's add method returns Validator instance, therefore we can chain it to do something like this.

TextFormField(
    validator: Validator<String>()
        .add(RequiredRule())
        .add(EmailRule())
)

Via addAll()

If you have multiple Rules to add and you do not want to chain the add method, then addAll method can be used as shown below:

TextFormField(
    validator: Validator<String>()
        .addAll([RequiredRule(), EmailRule()])
)

Remember

The Validator runs the Rule's in the order they are registered.

Specifying name of the entity

Validator also accepts the name of the entity/field on which it is run, this way it is able to customize its validation message and put the entityName provided in its constructor.

TextFormField(
    validator: Validator<String>(
      rules:[MinLengthRule(6)],
      entityName: 'Password',
    )
)

will produce a validation message like:

Password should be more than 6 characters

Transforming the message

Validator also accepts a function which can be used to transform the message that is returned after the validation of the input.

transformMessage function can be used for cases like localization among others.

By default, transformMessage replaces the keys in the message by the corresponding values which are defined in the params map.

Consider a situation where we want to change the case of the message to upperCase, it can be done as follows:

TextFormField(
    rules: [RequiredRule()],
    validator: Validator<String>(
        transformMessage: (String message, Map<String, String> params) =>
            message.toUpperCase();
    )
)

Remember

The Rule also accepts the transformMessage which takes precedence over the Validator's transformMessage.

← Rule →