ui state app

app.dart

import 'package:flutter/material.dart';

enum AppState { LOADING, COMPLETED, ERROR, IDEL }
void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHome(),
    );
  }
}

class MyHome extends StatefulWidget {
  const MyHome({Key? key}) : super(key: key);

  @override
  _MyHomeState createState() => _MyHomeState();
}

class _MyHomeState extends State<MyHome> {
  AppState uiState = AppState.LOADING;

  Future<void> _callApi() async {
    try {
      uiState = AppState.LOADING;
      setState(() {});
      await Future.delayed(Duration(seconds: 5)); // the api call and you can set the data from the api call
      uiState = AppState.COMPLETED;
      setState(() {});
      // to test the error state you can trow an error
    } catch (e) {
      uiState = AppState.ERROR;
      setState(() {});
    }
  }

  Future<void> _retry() async {
    /// you can add your retry stuff
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Builder(
          builder: (ctx) {
            switch (uiState) {
              case AppState.LOADING:
                return Center(child: CircularProgressIndicator());
              case AppState.COMPLETED:
                return Column(
                  children: [
                    Text("APP IS READY"),
                  ],
                );
              case AppState.ERROR:
                return Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    Text("APP HAS ERROR"),
                    TextButton(
                      onPressed: _retry,
                      child: Text("RETRY"),
                    ),
                  ],
                );
              default:
                return Container();
            }
          },
        ),
      ),
    );
  }
}