Reusing input validator - flutter

Question

I'm trying to create a logic for reusing multiple input validator at once. Here is DartPad code
void main() {
String value = 'pppppp';
print(InputValidator([InputValidator.minCharacters(value, 2),
InputValidator.maxCharacters(value, 5)
]).validate().toString());
}
class InputValidator {
final List<String> validators;
InputValidator(this.validators);
List<String> validate() {
List<String> result = [];
validators.where((s) => s != null).forEach(result.add);
return result;
}
static String maxCharacters(String value, int limit) {
if (value.length > limit) {
return 'Max $limit characters allowed';
}
return null;
}
static String minCharacters(String value, int limit) {
if (value.length < limit) {
return 'Min $limit characters required';
}
return null;
}
}
the logic works great however I'm trying to make it even easier where I wouldn't need to pass value into each method. I want to make value parameter in InputValidator class and take that value when running a method. Problem is that each method is static so I can not use that parameter in method.. Is there any other way?
Here is how I would like to use it
validator: InputValidator(value, [InputValidator.minCharacters(2),
InputValidator.maxCharacters(5)
]).validate()

Answer 1

Once again thanks to #pskink where he pointed out on FormFieldValidator. With that it is very simple to reuse validating of TextFormField.
Here is validator class
FormFieldValidator<String> all(Iterable validators) {
return (String s) {
var error = validators
.map((v) => v(s))
.where((error) => error != null)
.join(' AND ');
return error.isEmpty? null : error;
};
}
FormFieldValidator<String> uppercase() {
return (String s) => s.startsWith(RegExp('[A-Z]'))? null : 'does not start with uppercase' ;
}
FormFieldValidator<String> limit(min, max) {
return (String s) => (min <= s.length && s.length <= max)? null : 'length not in range [$min..$max]';
}
and here how to use it
Column(
children: [
Form(key: _formKey, child: TextFormField(validator:all([limit(2,5), uppercase()]))),
FlatButton(child:Text('Validate'), onPressed: (){if(_formKey.currentState.validate())
{print('OK');}}),
],
);