AsyncValidator<T> typedef

AsyncValidator<T> = FutureOr<String?> Function(T? value, AsyncValidatorOptions options)

A function represents async validation invocation.

It takes target value, which may be null, and then returns validation error message if the value is not valid, or returns null if the value is valid.

options is AsyncValidatorOptions which has options for validators such as Locale to localize error message.

Implementation

typedef AsyncValidator<T> = FutureOr<String?> Function(
  T? value,
  AsyncValidatorOptions options,
);