Form-level state

AdvancedFormController is a ValueListenable of AdvancedFormState — bind canSubmit, wasModified, and validation to the UI.

AdvancedFormController is itself a ValueListenable<AdvancedFormState>, so form-wide state renders the same way a field does:

ValueListenableBuilder<AdvancedFormState>(
  valueListenable: form,
  builder: (context, state, _) => ElevatedButton(
    onPressed: state.wasModified ? form.submit : null,
    child: const Text('Submit'),
  ),
);

AdvancedFormState carries wasModified (any field changed since registerFields), fields / subforms, validationEnabled, and validationMode — the configured mode, not reduced by validationEnabled. Four members are derived from the fields on every read, so they never report a field or subform that has since been removed:

Member	Meaning
`validating`	An async check is in flight somewhere in the tree
`canSubmit`	Every field is `valid` right now — a snapshot of known errors, so it is true on a quiet form nobody has checked yet, and false while any check is pending or in flight. `await form.validate()` is the guarantee
`hasFailedValidation`	Some field's async check could not run — it threw or timed out. Drives one form-level banner
`validationErrors`	Every error in the form tree, sync or async, keyed by field, for an error summary

With provider, context.select<SignupFormController, bool>((c) => c.value.validating) subscribes to one slice.

To react outside a builder, form.onValuesChanged and form.onStatusChanged are Listenables covering the whole tree, subforms included. Pass a named callback so you can removeListener it later.

AdvancedFormController takes two optional constructor arguments: debugName, a label for logging across nested subforms, and validateAll — when true, a change to any field re-runs the sync validator on every other autovalidating field, which is what you want when fields validate against each other. No async check is restarted: a field whose own value did not change keeps its last answer, so typing starts no async checks. It is the blunt version of subscribeToFields, reaching the whole tree instead of the dependencies you name.