Custom Rule

Validasi provides a way to create a custom rule by using the custom and customFor method. The custom rule will then be called when the built-in rules already performed. For details, see Execution Flow.

custom Method

The custom method will receive a function that will be called when the validation is performed.

import 'package:validasi/validasi.dart';

Validasi.string().custom((value, fail) {});

customFor Method

The customFor method will receive a class instance that implements the CustomRule interface. This method is useful when you want to create a custom rule that can be reused in multiple schemas.

main.dart

import 'package:validasi/validasi.dart';
import 'package:app/rules/my_rule.dart';

Validasi.string().customFor(MyRule()); 

my_rule.dart

import 'dart:async';
import 'package:validasi/validasi.dart';

class MyRule extends CustomRule<String> { 
    @override
    FutureOr<bool> handle(value, fail) {
        return true;
    }
}

Asyncronous Custom Rule

You can also run an async function inside the custom rule.

import 'package:validasi/validasi.dart';
import 'package:app/data.dart';

void main() {
    final schema = Validasi.string().custom((value, fail) async {
        if (await Data.user().contains(value)) {
            return true;
        }

        return fail('Ups, not hello');
    });

    final result = schema.tryParseAsync('world');
}

Keep in mind when running async rule, you need to use the async variants instead (e.g. tryParseAsync, parseAsync).

The Method Signature

Both the custom and handle method share similar signature. The value parameter is the value that will be validated by your custom rule. The fail parameter is a function that you can call when the validation failed.

Both methods expects FutureOr<bool> as the return type. You can return true to indicate that the validation passed or false to indicate that the validation failed. You can also return a Future<bool> if you want to run an async since FutureOr is a union type of Future and T.

The fail parameter is a function that will receive a message that will be used as the error message. The fail function will return false to indicate that the validation failed. Alternatively, you can just return false this will fallback to default error message: field is not valid.

INFO

When running async rule in a non-async parse variants (e.g. tryParse, parse), Validasi will throw an exception.