Provider (Check Age) Example

 import "package:firebase/Stateless_Component_UI/Provider/Providers/home_page_provider.dart";

import "package:flutter/material.dart";
import "package:provider/provider.dart";

void main()
{
  runApp(const MyApp());
}
class MyApp extends StatelessWidget
{
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Provider App",
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.grey,
      ),
      home: const HomePage2(),
    );
  }
}

class HomePage2 extends StatefulWidget
{
  const HomePage2({super.key});
  @override
  State<HomePage2> createState()
  {
    return HomePage2State();
  }
}
class HomePage2State extends State<HomePage2>
{
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("This is Home Page"),
        centerTitle: true,
        backgroundColor: Colors.grey,
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(200.0),
          child: ChangeNotifierProvider<HomePageProvider>(
            create: (context) {
              return HomePageProvider();
            },
            child: Consumer<HomePageProvider>(
              builder: (context, provider, child) {
                return Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: <Widget>[
                    Text(provider.eligibilityMessage.toString(),
                      style: TextStyle(color: (provider.isEligible == true) ? Colors.green : Colors.red),
                    ),
                    const SizedBox(height: 20.0),
                    TextFormField(
                      decoration: InputDecoration(
                        hintText: "Enter your age",
                        labelText: "age",
                        border: OutlineInputBorder(
                          borderRadius: BorderRadius.circular(11.0),
                        ),
                      ),
                      onChanged: (value) {
                        provider.checkEligibility(int.parse(value));
                        if(provider.isEligible == true)
                          {
                            ScaffoldMessenger.of(context).showSnackBar(
                              const SnackBar(content: Text("You are Eligible!"),),);
                          }
                      },
                    ),
                  ],
                );
              },
            ),
          ),
        ),
      ),
    );
  }
}

import "package:flutter/material.dart";

class HomePageProvider with ChangeNotifier
{
  bool? isEligible;
  String? eligibilityMessage = "";

  void checkEligibility(int age)
  {
    if(age >= 18)
      {
        isEligible = true;
        eligibilityMessage = "You are Eligible";
        notifyListeners();
      }
    else
      {
        isEligible = false;
        eligibilityMessage = "You are not Eligible";
        notifyListeners();
      }
  }
}