example.md

Just use the validate function to execute the list of predefined validators

    TextFormField(
	    validator: validate([
		    Required('This field is required'),
		    Email('Please enter the email correctly'),
    ]))

and the validator function will be executed using either the global key of the Form widget or the Form Field, click Here for more information about flutter validation.

please note that the validators functions will be executed in the same order that was defined

the validators are simple functions that returns true when the value is not as supposed so you can build your validators the works the same as the predefined ones

class BadWordValidator implements IValidator {
  String message = 'Message to be used as error message';
  BadWordValidator([this.message]);
  call(String value) {
    return value != "BadWord" ? false : true;
  }
}

also, you can always see the source code to learn more.

The last thing that you can use a 3rd lib to facilitate the process, you can see this one, here's one of it's function isDate() that validates if the string is date, because it's a function that returns boolean we can use it with our interface to form a validator function, like this:

	 class IsDate implements IValidator {
		 final String message = 'Message to be used as error message';
		 IsDate(this.message);
		 call(String value) {
			 return isDate(value);
		}
	}
		
    TextFormField(
	    key: myFormKey,
	    validator: validate([
		    IsDate('Please enter correct date')
    ]))