15. Singleton 주입 → DependencyInjection

✔️  Singleton 주입

• Logger 같은 전역 서비스(Singleton)를 ViewModel에 안전하게 주입하여 사용합니다.
• MVVM에서 Logger.Instance를 직접 참조하지 않고, 인터페이스 기반으로 느슨한 결합을 유지합니다.

✔️ "Singleton 주입"을, DependencyInjection 기반으로 확장

• App.xaml.cs에서 DI 컨테이너를 구성하고,
• ILoggerService를 싱글톤으로 등록해 MainViewModel, SubViewModel에 자동으로 주입됩니다.
• App.xaml.cs에서 ServiceCollection을 구성하고 ILoggerService, MainViewModel, SubViewModel을 등록
• MainWindow.xaml.cs, SubWindow.xaml.cs에서 Ioc.Default.GetRequiredService<T>()로 ViewModel 주입
• ViewModel 생성자는 그대로 ILoggerService를 받음

📁 Message 구현

WPF_Singleton04_03MVVM/
  ├── Messages/
  │   ├── LogUpdateMessage.cs
//├── Services/
//│   ├── ILoggerService.cs
//│   └── Logger.cs            ← Singleton 구현
//├── ViewModels/
//│   └── MainViewModel.cs
//│   └── SubViewModel.cs
//├── Views/
//│   └── MainWindow.xaml
//│   └── MainWindow.xaml.cs
//│   └── SubWindow.xaml
//│   └── SubWindow.xaml.cs
//└── App.xaml.cs

✔️ LogUpdateMessage 메시지 구현

// 메시지 정의
public class LogUpdateMessage : ValueChangedMessage<string>
{
    public LogUpdateMessage(string value) : base(value) { }
}

📁 Services 구현

WPF_Singleton04_03MVVM/
//├── Messages/
//│   ├── LogUpdateMessage.cs
  ├── Services/
  │   ├── ILoggerService.cs
  │   └── Logger.cs            ← Singleton 구현
//├── ViewModels/
//│   └── MainViewModel.cs
//│   └── SubViewModel.cs
//├── Views/
//│   └── MainWindow.xaml
//│   └── MainWindow.xaml.cs
//│   └── SubWindow.xaml
//│   └── SubWindow.xaml.cs
//└── App.xaml.cs

✔️ ILoggerService 인터페이스 구현

public interface ILoggerService
{
    void Log(string message);
    string GetLogs();
}

✔️ Logger 클래스 구현

public sealed class Logger : ILoggerService
{
    private static Logger? _instance = null;
    private static readonly object _lock = new();
    private readonly StringBuilder _logs = new();
 
    private Logger()
    {
        Console.WriteLine("Logger 인스턴스가 생성되었습니다.");
    }
 
    public static Logger Instance
    {
        get
        {
            lock (_lock)
            {
                return _instance ??= new Logger();
            }
        }
    }
 
    public void Log(string message)
    {
        string log = $"{DateTime.Now:HH:mm:ss} - {message}";
        _logs.AppendLine(log);
        // 로그가 업데이트되면 메시지를 발송하여 ViewModel에 알림
        WeakReferenceMessenger.Default.Send(new LogUpdateMessage(_logs.ToString()));
    }
 
    public string GetLogs()
    {
        return _logs.ToString();
    }
}

📁 ViewModel 구현

WPF_Singleton04_03MVVM/
//├── Messages/
//│   ├── LogUpdateMessage.cs
//├── Services/
//│   ├── ILoggerService.cs
//│   └── Logger.cs            ← Singleton 구현
  ├── ViewModels/
  │   └── MainViewModel.cs
  │   └── SubViewModel.cs
//├── Views/
//│   └── MainWindow.xaml
//│   └── MainWindow.xaml.cs
//│   └── SubWindow.xaml
//│   └── SubWindow.xaml.cs
//└── App.xaml.cs

✔️ MainViewModel 구현

public partial class MainViewModel : ObservableObject
{
    private readonly ILoggerService _logger;
 
    [ObservableProperty]
    private string logText;
 
    public MainViewModel(ILoggerService logger)
    {
        _logger = logger;
        _logger.Log("MainWindow 열림");
        LogText = _logger.GetLogs();
 
        // 메시지 수신 등록
        WeakReferenceMessenger.Default.Register<LogUpdateMessage>(this, (r, m) =>
        {
            LogText = m.Value;
        });
    }
 
    [RelayCommand]
    private void WriteLog()
    {
        _logger.Log("MainWindow에서 로그 기록");
        var logs = _logger.GetLogs();
        LogText = logs;
        WeakReferenceMessenger.Default.Send(new LogUpdateMessage(logs));
    }
 
    [RelayCommand]
    private void OpenSubWindow()
    {
        var sub = new SubWindow();
        sub.Show();
    }
}

✔️ SubViewModel 구현

public partial class SubViewModel : ObservableObject
{
    private readonly ILoggerService _logger;
 
    [ObservableProperty]
    private string logText;
 
    public SubViewModel(ILoggerService logger)
    {
        _logger = logger;
        _logger.Log("SubWindow 열림");
        LogText = _logger.GetLogs();
 
        WeakReferenceMessenger.Default.Register<LogUpdateMessage>(this, (r, m) =>
        {
            LogText = m.Value;
        });
    }
 
    [RelayCommand]
    private void WriteLog()
    {
        _logger.Log("SubWindow에서 로그 기록");
        var logs = _logger.GetLogs();
        LogText = logs;
        WeakReferenceMessenger.Default.Send(new LogUpdateMessage(logs));
    }
}

📁 View 구현

WPF_Singleton04_03MVVM/
//├── Messages/
//│   ├── LogUpdateMessage.cs
//├── Services/
//│   ├── ILoggerService.cs
//│   └── Logger.cs            ← Singleton 구현
//├── ViewModels/
//│   └── MainViewModel.cs
//│   └── SubViewModel.cs
  ├── Views/
  │   └── MainWindow.xaml
  │   └── MainWindow.xaml.cs
  │   └── SubWindow.xaml
  │   └── SubWindow.xaml.cs
//└── App.xaml.cs

✔️ MainWindow.xaml 구현

    Title="MainWindow" Height="300" Width="400">
<StackPanel Margin="10">
    <Button Content="로그 남기기" Command="{Binding WriteLogCommand}" Margin="0 0 0 10"/>
    <Button Content="SubWindow 열기" Command="{Binding OpenSubWindowCommand}" Margin="0 0 0 10"/>
    <TextBox Text="{Binding LogText}" AcceptsReturn="True" Height="200" VerticalScrollBarVisibility="Auto"/>
</StackPanel>

✔️ MainWindow.xaml.cs 구현

public MainWindow()
{
    InitializeComponent();
 
    //DataContext = new MainViewModel(Logger.Instance);
   DataContext = Ioc.Default.GetService<MainViewModel>();
}

✔️ SubWindow 구현

    Title="SubWindow" Height="250" Width="350">
<StackPanel Margin="10">
    <Button Content="로그 남기기" Command="{Binding WriteLogCommand}" Margin="0 0 0 10"/>
    <TextBox Text="{Binding LogText}" AcceptsReturn="True" Height="150" VerticalScrollBarVisibility="Auto"/>
</StackPanel>

✔️ SubWindow.xaml.cs 구현

public SubWindow()
{
    InitializeComponent();
 
   //DataContext = new SubViewModel(Logger.Instance);
   DataContext = Ioc.Default.GetService<SubViewModel>();
}

📁 Services 구현

WPF_Singleton04_03MVVM/
//├── Messages/
//│   ├── LogUpdateMessage.cs
//├── Services/
//│   ├── ILoggerService.cs
//│   └── Logger.cs            ← Singleton 구현
//├── ViewModels/
//│   └── MainViewModel.cs
//│   └── SubViewModel.cs
//├── Views/
//│   └── MainWindow.xaml
//│   └── MainWindow.xaml.cs
//│   └── SubWindow.xaml
//│   └── SubWindow.xaml.cs
  └── App.xaml.cs

✔️ App.xaml.cs 구현

protected override void OnStartup(StartupEventArgs e)
{
    base.OnStartup(e);
 
    // IoC 컨테이너에 싱글톤 Logger 등록
    Ioc.Default.ConfigureServices(
        new ServiceCollection()
            .AddSingleton<ILoggerService>(Logger.Instance)
            .AddTransient<MainViewModel>()
            .AddTransient<SubViewModel>()
            .BuildServiceProvider()
    );
 
    var mainWindow = new MainWindow();
    mainWindow.Show();
}

✔️ 소스코드