Unsaved-changes guard

Goal: while an editor has unsaved changes, block back — gesture, system button, and context.pop() alike — and show a “discard?” dialog.

Mix RouteGuard into the route. canPop is read synchronously (predictive back needs a sync answer); rebuildOn re-evaluates it as state changes; onPopBlocked runs when a blocked back is attempted.

class Editor extends AppRoute with RouteGuard {
  const Editor();

  @override
  bool get canPop => !formState.isDirty;

  @override
  Listenable? get rebuildOn => formState; // re-check when the form changes

  @override
  void onPopBlocked(BuildContext context) async {
    final discard = await showDialog<bool>(
      context: context,
      builder: (_) => AlertDialog(
        content: const Text('Discard unsaved changes?'),
        actions: [
          TextButton(onPressed: () => Navigator.pop(context, false), child: const Text('Keep')),
          TextButton(onPressed: () => Navigator.pop(context, true), child: const Text('Discard')),
        ],
      ),
    );
    if (discard == true) {
      formState.reset();          // clears isDirty → canPop becomes true
      if (context.mounted) context.pop();
    }
  }
}

Notes

• raku_router wraps a guarded screen in a PopScope, so the guard is honoured by the predictive-back gesture, an imperative Navigator.pop, the system back button, and the Router’s popRoute — onPopBlocked fires on all of them.
• For redirecting into a screen (e.g. auth), use a redirect instead.