CommunityToolkit.Mvvm 实战 (1) — 完整便签应用

// Models/Note.cs
public class Note
{
    public int Id { get; set; }
    public string Title { get; set; } = "";
    public string Content { get; set; } = "";
    public DateTime CreatedAt { get; set; } = DateTime.Now;
    public bool IsCompleted { get; set; }
}

// Services/INoteService.cs
public interface INoteService
{
    Task<List<Note>> GetAllAsync();
    Task<Note?> GetByIdAsync(int id);
    Task SaveAsync(Note note);
    Task DeleteAsync(int id);
}

// Services/NoteService.cs
public class NoteService : INoteService
{
    private List<Note> _notes = new();
    private int _nextId = 1;

    public Task<List<Note>> GetAllAsync()
        => Task.FromResult(_notes.ToList());

    public Task<Note?> GetByIdAsync(int id)
        => Task.FromResult(_notes.FirstOrDefault(n => n.Id == id));

    public Task SaveAsync(Note note)
    {
        if (note.Id == 0)
        {
            note.Id = _nextId++;
            _notes.Add(note);
        }
        else
        {
            var index = _notes.FindIndex(n => n.Id == note.Id);
            if (index >= 0) _notes[index] = note;
        }
        return Task.CompletedTask;
    }

    public Task DeleteAsync(int id)
    {
        _notes.RemoveAll(n => n.Id == id);
        return Task.CompletedTask;
    }
}

// ViewModels/MainViewModel.cs
public partial class MainViewModel : ObservableRecipient
{
    private readonly INoteService _noteService;

    // 当前显示的子 ViewModel
    [ObservableProperty]
    private object? _currentViewModel;

    // 从 IServiceProvider 注入依赖
    public MainViewModel(INoteService noteService,
        NoteListViewModel noteList,
        NoteDetailViewModel noteDetail)
    {
        _noteService = noteService;

        // 注册消息接收
        IsActive = true;
    }

    // 接收导航消息
    protected override void OnActivated()
    {
        // 注册导航请求
        Messenger.Register<NavigateToDetailMessage>(this, (r, m) =>
        {
            var vm = (MainViewModel)r;
            var detail = App.Services.GetRequiredService<NoteDetailViewModel>();
            detail.LoadNote(m.NoteId);
            vm.CurrentViewModel = detail;
        });

        Messenger.Register<NavigateToListMessage>(this, (r, m) =>
        {
            var vm = (MainViewModel)r;
            vm.CurrentViewModel = App.Services.GetRequiredService<NoteListViewModel>();
        });

        // 初始加载列表
        CurrentViewModel = App.Services.GetRequiredService<NoteListViewModel>();
    }
}

// 定义导航消息
public sealed record NavigateToDetailMessage(int NoteId);
public sealed record NavigateToListMessage;

// ViewModels/NoteListViewModel.cs
public partial class NoteListViewModel : ObservableObject
{
    private readonly INoteService _noteService;

    [ObservableProperty]
    private List<Note> _notes = new();

    [ObservableProperty]
    private bool _isLoading;

    [ObservableProperty]
    private string _statusText = "就绪";

    // ---- 加载命令（AsyncRelayCommand） ----
    [RelayCommand]
    private async Task LoadNotesAsync()
    {
        IsLoading = true;
        StatusText = "加载中...";
        try
        {
            Notes = await _noteService.GetAllAsync();
            StatusText = $"共 {Notes.Count} 条便签";
        }
        catch (Exception ex)
        {
            StatusText = $"加载失败: {ex.Message}";
        }
        finally
        {
            IsLoading = false;
        }
    }

    // ---- 添加命令 ----
    [RelayCommand]
    private void AddNote()
    {
        WeakReferenceMessenger.Default.Send(
            new NavigateToDetailMessage(0)); // 0 = 新建
    }

    // ---- 编辑命令（泛型参数） ----
    [RelayCommand]
    private void EditNote(Note? note)
    {
        if (note is null) return;
        WeakReferenceMessenger.Default.Send(
            new NavigateToDetailMessage(note.Id));
    }

    // ---- 删除命令（异步 + 确认） ----
    [RelayCommand(CanExecute = nameof(CanDeleteNote))]
    private async Task DeleteNoteAsync(Note? note)
    {
        if (note is null) return;
        await _noteService.DeleteAsync(note.Id);
        await LoadNotesAsync();
    }
    private bool CanDeleteNote(Note? note) => note is not null;

    // ---- 构造后自动加载 ----
    public NoteListViewModel(INoteService noteService)
    {
        _noteService = noteService;
    }
}

// ViewModels/NoteDetailViewModel.cs
public partial class NoteDetailViewModel : ObservableValidator
{
    private readonly INoteService _noteService;
    private int _noteId;

    [ObservableProperty]
    [Required(ErrorMessage = "标题不能为空")]
    [MinLength(1)]
    [NotifyDataErrorInfo]
    private string _title = "";

    [ObservableProperty]
    private string _content = "";

    [ObservableProperty]
    private bool _isSaving;

    // 加载便签
    public async void LoadNote(int noteId)
    {
        _noteId = noteId;
        if (noteId == 0) return; // 新建

        var note = await _noteService.GetByIdAsync(noteId);
        if (note is null) return;

        Title = note.Title;
        Content = note.Content;
    }

    // ---- 保存命令（AsyncRelayCommand + 验证） ----
    [RelayCommand]
    private async Task SaveAsync()
    {
        // 先验证
        ValidateAllProperties();
        if (HasErrors) return;

        IsSaving = true;
        try
        {
            var note = new Note
            {
                Id = _noteId,
                Title = Title,
                Content = Content,
                CreatedAt = DateTime.Now
            };
            await _noteService.SaveAsync(note);
            WeakReferenceMessenger.Default.Send(new NavigateToListMessage());
        }
        finally
        {
            IsSaving = false;
        }
    }

    // ---- 取消命令 ----
    [RelayCommand]
    private void Cancel()
    {
        WeakReferenceMessenger.Default.Send(new NavigateToListMessage());
    }

    public NoteDetailViewModel(INoteService noteService)
    {
        _noteService = noteService;
    }
}

// App.xaml.cs
public partial class App : Application
{
    public static IServiceProvider Services { get; private set; } = null!;

    protected override void OnStartup(StartupEventArgs e)
    {
        var services = new ServiceCollection();

        // 注册服务
        services.AddSingleton<INoteService, NoteService>();

        // 注册 ViewModel（Transient：每次导航创建新实例）
        services.AddTransient<NoteListViewModel>();
        services.AddTransient<NoteDetailViewModel>();
        services.AddTransient<MainViewModel>();

        // 注册窗口
        services.AddSingleton<MainWindow>();

        Services = services.BuildServiceProvider();

        // 启动
        var mainWindow = Services.GetRequiredService<MainWindow>();
        mainWindow.DataContext = Services.GetRequiredService<MainViewModel>();
        mainWindow.Show();
    }
}