Form scope and context

Publish a controller and field registry to descendants and use the correct BuildContext for lookups and submit.

KeyedForm<Root> publishes its KeyedFormController<Root>, owns the field-anchor registry, and installs the reactive scope used by context selectors. KeyedForm.controllerOf, registryOf, and translateErrorOf perform an ambient lookup: their context must be below the matching KeyedForm in the widget tree.

A State.context that created the KeyedForm is above it and cannot perform that lookup. Use a descendant builder context instead:

dart

KeyedForm<InvoiceSchema>(
  controller: form,
  child: Builder(
    builder: (formContext) => FilledButton(
      onPressed: () => form.handleSubmit(formContext, saveInvoice),
      child: const Text('Save'),
    ),
  ),
)

handleSubmit also requires this descendant context. By default it reveals the first visible error using the registry owned by the form; a supplied onInvalid callback takes responsibility for invalid handling instead. The registry and form scope are created and disposed with the KeyedForm state; the controller is passed in by the application. Keep ownership clear: dispose a controller you created when its owning screen is disposed, not from an arbitrary field builder.

translateError is a stable, non-reactive function reference. Changing its identity does not re-propagate a new translator through existing descendants. See submit and scroll to error and field bindings.