ChangeNotifier

main.dart

import 'package:flutter/material.dart';

void main() {
  print("Hello World!");
  var notifier = TestNotifier();
  
  var listener1 = () {
    print("Inside listener 1");
  };
  
  var listener2 = () {
    print("Inside listener 2");
  };
  
  notifier.addListener(listener1);
  notifier.addListener(listener1);
  
  notifier.pingListeners();
}

class TestNotifier extends ChangeNotifier {
   void pingListeners() {
     this.notifyListeners();
   }
}