await and unawaited requests in dart

unawait_demo.dart

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Data Loading Example',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool _mainDataLoading = true;
  bool _secondaryDataLoading = true;
  List _mainData = [];
  List _secondaryData = [];

  @override
  void initState() {
    super.initState();
    loadData();
  }

  Future<void> loadData() async {
    try {
      setState(() {
        _mainDataLoading = true;
        _secondaryDataLoading = true;
      });

      // Wait for critical main data to load
      _mainData = await loadMainData();

      // Start loading secondary data without waiting
      unawaited(_loadSecondaryData().whenComplete(() {
        setState(() {
          _secondaryDataLoading = false;
        });
      }));
    } on Exception catch (error) {
      print('Error loading data: $error');
    } finally {
      setState(() {
        _mainDataLoading = false;
      });
    }
  }

  Future<List> loadMainData() async {
    await Future.delayed(Duration(seconds: 2)); // Simulate data loading time
    return ['Item 1', 'Item 2', 'Item 3'];
  }

  Future<void> _loadSecondaryData() async {
    await Future.delayed(Duration(seconds: 3)); // Simulate data loading time
    setState(() {
      _secondaryData = ['Item A', 'Item B', 'Item C'];
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Data Loading Example'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            _mainDataLoading
                ? CircularProgressIndicator()
                : Text('Main Data: ' + _mainData.join(', ')),
            SizedBox(height: 20),
            _secondaryDataLoading
                ? CircularProgressIndicator()
                : Text('Secondary Data: ' + _secondaryData.join(', ')),
          ],
        ),
      ),
    );
  }
}