[Flutter] Provider 상태에 따른 추가 액션(with addListener)

오늘은 Provider 구현시, 상태에 따라서 추가적인 액션이 필요한 경우에 대한 구조입니다.

개발환경 : 윈도우11, 안드로이드 스튜디오(Arctic Fox 2020.3.1 Patch 4), flutter 2.10

소스코드 - Release 35_ChangeNotifier_addListener4 · mike-bskim/provider_overview · GitHub

Release 35_ChangeNotifier_addListener4 · mike-bskim/provider_overview

 

main.dart

 

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

import 'app_provider.dart';
import 'success_page.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<AppProvider>(
      create: (_) => AppProvider(),
      child: MaterialApp(
        title: 'addListener of ChangeNotifier',
        debugShowCheckedModeBanner: false,
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: const MyHomePage(),
      ),
    );
  }
}

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

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final GlobalKey<FormState> formKey = GlobalKey<FormState>();
  AutovalidateMode autovalidateMode = AutovalidateMode.disabled;
  String? searchTerm;
  late final AppProvider appProv;

  @override
  void initState() {
    super.initState();
    appProv = context.read<AppProvider>();
    appProv.addListener(appListener);
  }

  // appListener 에서 상태를 체크해야해서, appProv 객체를 만들어야 한다
  void appListener() {
    if (appProv.state == AppState.success) {
      Navigator.push(context, MaterialPageRoute(
        builder: (context) {
          return const SuccessPage();
        },
      ));
    } else if (appProv.state == AppState.error) {
      showDialog(
        context: context,
        builder: (context) {
          return const AlertDialog(
            content: Text('Something went wrong'),
          );
        },
      );
    }
  }

  @override
  void dispose() {
    appProv.removeListener(appListener);
    super.dispose();
  }

  void submit() {
    setState(() {
      // 폼이 summit 된후, 모든 폼 입력에 대해서 항상 validation 확인
      autovalidateMode = AutovalidateMode.always;
    });

    final form = formKey.currentState;
    if (form == null || !form.validate()) return;
    form.save();
    context.read<AppProvider>().getResult(searchTerm!);
  }

  @override
  Widget build(BuildContext context) {
    final appState = context.watch<AppProvider>().state;

    return GestureDetector(
      onTap: () => FocusScope.of(context).unfocus(),
      child: Scaffold(
        body: Center(
          child: Padding(
            padding: const EdgeInsets.symmetric(horizontal: 30.0),
            child: Form(
              key: formKey,
              autovalidateMode: autovalidateMode,
              child: ListView(
                shrinkWrap: true,
                children: [
                  TextFormField(
                    autofocus: true,
                    decoration: const InputDecoration(
                      border: OutlineInputBorder(),
                      label: Text('Search'),
                      prefixIcon: Icon(Icons.search),
                    ),
                    validator: (String? value) {
                      if (value == null || value.trim().isEmpty) {
                        return 'Search term required';
                      }
                      return null;
                    },
                    onSaved: (String? value) {
                      searchTerm = value;
                    },
                  ),
                  const SizedBox(height: 20.0),
                  ElevatedButton(
                    child: Text(
                      appState == AppState.loading
                          ? 'Loading...'
                          : 'Get Result',
                      style: const TextStyle(fontSize: 24.0),
                    ),
                    onPressed: appState == AppState.loading ? null : submit,
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }
}

 

app_provider.dart

 

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:provider_overview/success_page.dart';

enum AppState {
  initial,
  loading,
  success,
  error,
}

class AppProvider with ChangeNotifier {
  AppState _state = AppState.initial;
  AppState get state => _state;

  Future<void> getResult(String searchTerm) async {
    _state = AppState.loading;
    notifyListeners();

    await Future.delayed(const Duration(seconds: 1));

    try {
      if (searchTerm == 'fail') {
        throw 'Something went wrong';
      }
      _state = AppState.success;
      notifyListeners();
    } catch (e) {
      _state = AppState.error;
      notifyListeners();
    }
  }
}

 

success_page.dart

 

import 'package:flutter/material.dart';

class SuccessPage extends StatelessWidget {
  const SuccessPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Success'),
      ),
      body: const Center(
        child: Text(
          'Success',
          style: TextStyle(fontSize: 48.0),
        ),
      ),
    );
  }
}

 

 

 

 

[참고자료] udemy - Flutter Provider Essential 코스 (Korean)