Prefilled forms

wasModified compares each field's value with its value at registerFields time. A controller that registers fields in its constructor and then loads server data reports wasModified: true forever, and a "Save" button gated on it is live from the start. Press both buttons below and watch the wasModified chip.

class EditProfileController extends AdvancedFormController {
  EditProfileController() {
    registerFields([name, email]); // baseline: both empty
  }

  final name = AdvancedTextFieldController(validator: filled('Required'));
  final email = AdvancedTextFieldController(validator: filled('Required'));

  /// Writes the loaded values without arming validation — but they differ
  /// from the empty baseline, so wasModified becomes true.
  Future<void> loadWithPrefill() async {
    final profile = await _fetchProfile();
    name.prefill(profile.name);
    email.prefill(profile.email);
  }

  /// The same, then registers the same fields again so the loaded values
  /// become the new baseline: wasModified is false until the user edits.
  Future<void> loadAndRebaseline() async {
    await loadWithPrefill();
    registerFields([name, email]);
  }

  Future<({String name, String email})> _fetchProfile() async {
    await Future<void>.delayed(const Duration(milliseconds: 400));
    return (name: 'Ada Lovelace', email: 'ada@example.com');
  }
}

Two ways to get the baseline right

1. Build the field controllers with the loaded data as initialValue:. The form is constructed after the data arrives, wasModified starts false, and reset() returns to the loaded values — which is what a Discard button should do. Preferred whenever the form has one.
2. Re-call registerFields(sameList) once the data has arrived, as above. Re-baselining does not move reset(): that always returns to the constructor's initialValue, so after a re-baseline resetAll() lands off the baseline and flips wasModified back to true.

prefill versus setValue

Both write the value and clear both errors. setValue also marks the field as edited by the user, which is what lets a validation mode fire; prefill does not, so a bad value from the server shows no error until submit — where validate() still catches it. Both count towards wasModified, because both change the value.