enhanced_change_notifier

Support for targeted notifications on object property changes.

Enhanced ChangeNotifiers introduce three new features in addition to all existing ChangeNotifier capabilities in Flutter Core:

• target: notifies listeners at the moment a specified property changes.
• once: notifies listeners only once at the moment of a change.
• immediate: allows notifications to be sent immediately after a listener is registered and upon subsequent changes.

Platform Support

Requirements

• Flutter >=3.0.0 <4.0.0
• Dart >=2.17.0

Getting started

published on pub.flutter-io.cn, run this Flutter command

flutter pub add enhanced_change_notifier

Usage in Dart

Multiple properties or Mutable data types, extending EnhancedChangeNotifier directly to meet flexible requirements like cache or targeted listener.

import 'package:enhanced_change_notifier/enhanced_change_notifier.dart';

class AppModel extends EnhancedChangeNotifier {
  String? _token;

  String? get token => _token;
  set token(String? token) {
    _token = token;
    notifyListeners("token");
  }
}

// GlobalFactory helps create a global singleton instance.
final GlobalFactory<AppModel> appStateModel = GlobalFactory(() => AppModel());

function _e_anyChangedListener() {
  print("any property is changed");
}

function _e_tokenChangedListener(String property) {
  print("$property is changed");
}

function _e_onceListener(String property) {
  print("$property is changed, will notify only once.");
}

function _e_immediateListener(String property) {
  print("$property is changed, will send immediately after listener is registered.");
}

appStateModel.getInstance().addListener(_e_anyChangedListener);
appStateModel.getInstance().addListener(_e_tokenChangedListener, target: 'token');
appStateModel.getInstance().addListener(_e_onceListener, target: 'token', once: true);
appStateModel.getInstance().addListener(_e_immediateListener, target: 'token', immediate: true);

A single implementation buffers pipelined listener pending a release signal.

import 'package:enhanced_change_notifier/signal.dart';

Signal isConsumerReady = Signal();
isConsumerReady.value = false;

// delayed signal release
Future.delayed(Duration(milliseconds: 300), () {
isConsumerReady.value = true;
});

// register listener consumed immediately or awaited once via Signal(True).
isConsumerReady.promise(() => print("Task 1 executed"));
isConsumerReady.promise(() => print("Task 2 executed"));
isConsumerReady.promise(() => print("Task 3 executed"));

Additional information

Feel free to file an issue if you have any problem.