validator property

String? Function(String? value)? validator

Default:

(String? value) {
      if (controller.text.trim().length < 4 ||
          controller.text.trim().length > 255) {
        return "It should be 4 to 255 characters long.";
      } else if (!isEmailValid(controller.text.trim()) &&
             addEmailValidation!) {
           return 'Please enter a valid email address';
         }
      return null;
    },

Warning: Remember value is not trimmed one, so use textEditingController in case.

Implementation

final String? Function(String? value)? validator;