refactored error handling

Author: jorre127

lib/model/error_handling/result.dart

@@ -0,0 +1 @@
+typedef Result<T> = ({T? data, dynamic error});

lib/repository/error_handling/error_handling_repository_mixin.dart

@@ -0,0 +1,20 @@
+import 'package:flutter_template/model/error_handling/result.dart';
+import 'package:icapps_architecture/icapps_architecture.dart';
+
+mixin ErrorHandlingRepositoryMixin {
+  Future<Result<T>> fetch<T>({
+    required Future<T> Function() function,
+    required String errorMessage,
+  }) async {
+    T? data;
+    dynamic error;
+    try {
+      data = await function();
+    } catch (e) {
+      error = e;
+      staticLogger.e(errorMessage, error: error);
+    }
+
+    return (data: data, error: error);
+  }
+}

lib/repository/todo/todo_repository.dart

@@ -1,5 +1,9 @@
+import 'dart:async';
+
 import 'package:flutter_template/database/todo/todo_dao_storage.dart';
+import 'package:flutter_template/model/error_handling/result.dart';
 import 'package:flutter_template/model/webservice/todo/todo.dart';
+import 'package:flutter_template/repository/error_handling/error_handling_repository_mixin.dart';
 import 'package:flutter_template/webservice/todo/todo_service.dart';
 import 'package:injectable/injectable.dart';
 
@@ -10,14 +14,14 @@ abstract class TodoRepository {
 
   Stream<List<Todo>> getTodos();
 
-  Future<List<Todo>> fetchTodos();
+  Future<Result<List<Todo>>> fetchTodos();
 
   Future<void> saveTodo(String todo);
 
   Future<void> setTodoState({required int id, required bool value});
 }
 
-class _TodoRepository implements TodoRepository {
+class _TodoRepository with ErrorHandlingRepositoryMixin implements TodoRepository {
   final TodoDaoStorage _todoDao;
   final TodoService _todoService;
 
@@ -29,13 +33,16 @@ class _TodoRepository implements TodoRepository {
   ///Get Users will be requested from
   ///https://jsonplaceholder.typicode.com/todos
   @override
-  Future<List<Todo>> fetchTodos() async {
-    final results = await _todoService.getTodos();
-    for (final todo in results) {
-      await _todoDao.createTodoWithValue(todo);
-    }
-    return results;
-  }
+  Future<Result<List<Todo>>> fetchTodos() => fetch(
+        errorMessage: 'Failed to fetch todos',
+        function: () async {
+          final data = await _todoService.getTodos();
+          for (final todo in data) {
+            await _todoDao.createTodoWithValue(todo);
+          }
+          return data;
+        },
+      );
 
   @override
   Future<void> saveTodo(String todo) async {

lib/viewmodel/mixin/error_handling_mixin.dart

@@ -0,0 +1,28 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter_template/di/injectable.dart';
+import 'package:flutter_template/model/error_handling/result.dart';
+import 'package:flutter_template/navigator/main_navigator.dart';
+import 'package:icapps_architecture/icapps_architecture.dart';
+
+mixin ErrorHandlingViewModelMixin on ChangeNotifierEx {
+  MainNavigator get navigator => getIt();
+
+  Future<T?> failableFuture<T>(
+    Future<Result<T>> Function() future, {
+    ValueChanged<dynamic>? onError,
+    ValueChanged<bool>? onLoadingChanged,
+  }) async {
+    onLoadingChanged?.call(true);
+    notifyListeners();
+    final result = await future();
+    if (result.error != null) {
+      navigator.showError(result);
+      onError?.call(result.error);
+      return null;
+    }
+    onLoadingChanged?.call(false);
+    if (disposed) return null;
+    notifyListeners();
+    return result.data;
+  }
+}

lib/viewmodel/todo/todo_list/todo_list_viewmodel.dart

@@ -2,17 +2,19 @@ import 'package:flutter_template/model/webservice/todo/todo.dart';
 import 'package:flutter_template/navigator/main_navigator.dart';
 import 'package:flutter_template/repository/todo/todo_repository.dart';
 import 'package:flutter_template/util/locale/localization_keys.dart';
+import 'package:flutter_template/viewmodel/mixin/error_handling_mixin.dart';
 import 'package:icapps_architecture/icapps_architecture.dart';
 import 'package:injectable/injectable.dart';
 
 @injectable
-class TodoListViewModel with ChangeNotifierEx {
+class TodoListViewModel with ChangeNotifierEx, ErrorHandlingViewModelMixin {
   final MainNavigator _navigator;
   final TodoRepository _todoRepo;
 
   late Stream<List<Todo>> _todoStream;
 
   var _isLoading = false;
+
   String? _errorKey;
 
   bool get isLoading => _isLoading;
@@ -30,24 +32,13 @@ class TodoListViewModel with ChangeNotifierEx {
     _todoStream = _todoRepo.getTodos();
   }
 
-  Future<void> onDownloadClicked() async {
-    try {
-      _isLoading = true;
-      _errorKey = null;
-      notifyListeners();
-      await _todoRepo.fetchTodos();
-    } catch (e, stack) {
-      logger.error('failed to get todos', error: e, trace: stack);
-      if (e is LocalizedError) {
-        _errorKey = e.getLocalizedKey();
-      } else {
-        _errorKey = LocalizationKeys.errorGeneral;
-      }
-    } finally {
-      _isLoading = false;
-      notifyListeners();
-    }
-  }
+  Future<void> onDownloadClicked() => failableFuture(
+        _todoRepo.fetchTodos,
+        onError: (error) => _errorKey = _getErrorKeyFromError(error),
+        onLoadingChanged: (isLoading) => _isLoading = isLoading,
+      );
+
+  String _getErrorKeyFromError(dynamic error) => error is LocalizedError ? error.getLocalizedKey() : LocalizationKeys.errorGeneral;
 
   Future<void> onTodoChanged({required int? id, required bool value}) async {
     if (id == null) return;

test/repository/todo/todo_repository_test.dart

@@ -53,8 +53,8 @@ void main() {
   group('fetchTodos', () {
     test('fetchTodos', () async {
       when(todoService.getTodos()).thenAnswer((_) async => []);
-      final data = await sut.fetchTodos();
-      expect(data.isEmpty, true);
+      final result = await sut.fetchTodos();
+      expect(result.data?.isEmpty, true);
       verify(todoService.getTodos()).calledOnce();
       verifyNoMoreInteractions(todoService);
       verifyZeroInteractions(todoDao);
@@ -64,9 +64,9 @@ void main() {
             const Todo(id: 1, title: '2', completed: true),
             const Todo(id: 3, title: '3', completed: false),
           ]);
-      final data = await sut.fetchTodos();
-      expect(data.isNotEmpty, true);
-      expect(data.length, 2);
+      final result = await sut.fetchTodos();
+      expect(result.data?.isNotEmpty, true);
+      expect(result.data?.length, 2);
       verify(todoService.getTodos()).calledOnce();
       verify((todoDao as MockTodoDaoStorage).createTodoWithValue(any)).calledTwice();
     });