【C#/WPF実践入門編(10)】MVVMパターン/アーキテクチャの基礎② ～VisualStudioでフォルダ構成とサービス層で実務向け設計～

WpfCounterApp/
├── Commands/          # コマンド関連クラス
│   └── SimpleCommand.cs
├── Models/            # データモデル
│   └── CounterModel.cs
├── Services/          # ビジネスロジック・外部連携
│   └── JsonCounterStorage.cs
├── ViewModels/        # ViewModel
│   └── CounterViewModel.cs
├── Views/             # View（XAML + コードビハインド）
│   ├── CounterWindow.xaml
│   └── CounterWindow.xaml.cs
├── App.xaml
└── App.xaml.cs

<Window x:Class="WpfCounterApp.Views.CounterWindow"
...

using System.Windows;

namespace WpfCounterApp.Views
{
...

<Application x:Class="WpfCounterApp.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WpfCounterApp"
             StartupUri="Views/CounterWindow.xaml">
    <Application.Resources>
         
    </Application.Resources>
</Application>

using System.IO;
using System.Text.Json;

namespace WpfCounterApp.Services
{
    public class JsonCounterStorage
    {
        private const string FilePath = "counter.json";

        public int Load()
        {
            if (!File.Exists(FilePath)) return 0;

            var json = File.ReadAllText(FilePath);
            return JsonSerializer.Deserialize<int>(json);
        }

        public void Save(int value)
        {
            var json = JsonSerializer.Serialize(value);
            File.WriteAllText(FilePath, json);
        }
    }
}

    public class CounterModel
    {
        ...

        public CounterModel(int initialValue = 0)
        {
            Value = initialValue;
        }
        ...

using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows.Input;
using WpfCounterApp.Commands;
using WpfCounterApp.Models;
using WpfCounterApp.Services;

namespace WpfCounterApp.ViewModels
{
    public class CounterViewModel : INotifyPropertyChanged
    {
        private readonly CounterModel _model;
        private readonly JsonCounterStorage _storage; //★追加
        private readonly SimpleCommand _incrementCommand;
        private readonly SimpleCommand _decrementCommand;

        public CounterViewModel()
        {
            //★起動時、カウンター値を読み込む
            _storage = new JsonCounterStorage(); 
            int initialValue = _storage.Load(); 
            _model = new CounterModel(initialValue);

            _incrementCommand = new SimpleCommand(_ => ExecuteIncrement());
            _decrementCommand = new SimpleCommand(_ => ExecuteDecrement(), _ => _model.CanDecrement());
        }

        public int Count => _model.Value;

        public ICommand IncrementCommand => _incrementCommand;
        public ICommand DecrementCommand => _decrementCommand;

        private void ExecuteIncrement()
        {
            _model.Increment();
            OnPropertyChanged(nameof(Count));
            _storage.Save(_model.Value); //★変更後の値を保存
        }

        private void ExecuteDecrement()
        {
            _model.Decrement();
            OnPropertyChanged(nameof(Count));
            _storage.Save(_model.Value); //★変更後の値を保存
        }

        public event PropertyChangedEventHandler? PropertyChanged;

        protected void OnPropertyChanged([CallerMemberName] string? propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

            if (propertyName == nameof(Count))
            {
                _decrementCommand.RaiseCanExecuteChanged();
            }
        }
    }
}

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