FutureBuilder

 import "package:flutter/material.dart";

void main()
{
  runApp(MyApp());
}
class MyApp extends StatelessWidget
{
  MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "FutureBuilder Demo",
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: FutureDemo(),
    );
  }
}
class FutureDemo extends StatefulWidget
{
  FutureDemo({super.key});

  @override
  State<FutureDemo> createState()
  {
    return FutureDemoState();
  }
}
class FutureDemoState extends State<FutureDemo>
{
  /// Here below return type is String
  Future<String> getData() async {
    await Future.delayed(const Duration(seconds: 3),);
    return "Data";
  }

  /// Here below return type is integer
  // Future<int> getData() async {
  //   await Future.delayed(Duration(seconds: 3),);
  //   return 0;
  // }

  /// Here below return type is boolean
  // Future<bool> getData() async {
  //   await Future.delayed(Duration(seconds: 3),);
  //   return true;
  // }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Future Builder Demo"),
        centerTitle: true,
        backgroundColor: Colors.grey,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            ElevatedButton(
              onPressed: () {
                setState(() {
                  getData();
                },);
              },
              child: const Text("Click Here"),
            ),
            const SizedBox(height: 40.0),
            FutureBuilder(
              future: getData(),
              builder: (context, snapshot) {
                if(snapshot.connectionState == ConnectionState.waiting)
                  {
                    return const CircularProgressIndicator();
                  }
                else if(snapshot.connectionState == ConnectionState.done ||
                snapshot.connectionState == ConnectionState.active)
                  {
                    if(snapshot.hasError)
                      {
                        return Text(snapshot.error.toString());
                      }
                    else if(snapshot.hasData)
                      {
                        return Text(snapshot.data.toString());
                      }
                    else
                      {
                        return const Text("Something went Wrong!");
                      }
                  }
                else
                  {
                    return Text(snapshot.connectionState.toString());
                  }
              },
            ),
          ],
        ),
      ),
    );
  }
}