FUTURE API IN FLUTTER

main.dart

import 'package:flutter/material.dart';
import 'dart:async';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: FutureInFlutter(),
    );
  }
}

class FutureInFlutter extends StatefulWidget {
  @override
  _FutureInFlutterState createState() => _FutureInFlutterState();
}

class _FutureInFlutterState extends State<FutureInFlutter> {
  bool _isLoading = false;
  
  @override
  void initState() {
    print('initState()');
    super.initState();
    initApp();
  }

  initApp() async {
    print('initApp()');
    setState(() => _isLoading = true);
    Future.delayed(Duration(seconds: 6)).then((_) {
      print('setState()');
      setState(() => _isLoading = false);
    });
  }

  @override
  Widget build(BuildContext context) {
    print('build()');
    return Scaffold(
      appBar: AppBar(title: Text("Future Example")),
      body: Center(
          child: _isLoading
              ? CircularProgressIndicator()
              : Text("Future Completed!",
                  style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold))),
    );
  }
}