Custom controllers

The concrete base class

AdvancedFieldController<T, E> is not abstract. Construct it directly for any value with no dedicated controller — a slider, a stepper, a date, a rating, a derived total — and bind it like any other field. Scalars has a running slider.

final rating = AdvancedFieldController<int, MyError>(
  initialValue: 0,
  validator: (stars) => stars == 0 ? MyError.required : null,
  name: 'rating',
);

Ordinary user writes need no force: — that is only for writing to a field you have marked read-only.

Domain methods

Extend the base class — or AdvancedTextFieldController when the widget binds a text controller — to add methods on top of setValue:

class IntegerFieldController<E extends Object>
    extends AdvancedFieldController<int, E> {
  IntegerFieldController({
    super.initialValue = 0,
    super.validator,
    super.asyncValidation,
    super.name,
  });

  bool get isNegative => fieldValue.isNegative;

  void increment() => setValue(fieldValue + 1);
}

Transforming what the user types

To normalise, mask or upper-case, override setValue on a text controller. Every write to textController — keystroke, paste or programmatic — goes through the public setValue, so the override always runs, and the transformed value is written back into the text controller in the same turn:

class PhoneFieldController extends AdvancedTextFieldController<MyError> {
  PhoneFieldController({String initialValue = '', super.validator})
    : super(initialValue: _digits(initialValue));

  static String _digits(String value) => value.replaceAll(RegExp(r'\D'), '');

  @override
  void setValue(String newValue, {bool force = false}) =>
      super.setValue(_digits(newValue), force: force);
}

Normalise initialValue before it reaches super, as above: reset() returns to that value without passing through setValue.

A list as the error type

The example app's PasswordFieldController is a text field whose error type is a List, so one field reports several rule violations at once — Custom validators has a running version.