Avalonia .NET MVVM中如何为TextBlock绑定ICommand实现书籍添加

使用Avalonia MVVM开发C#应用，窗口左侧是按分类分组的书籍TreeView，右侧是已选书籍的DataGrid，需求是用户双击左侧书籍即可将其添加到右侧列表。尝试为TextBlock绑定ICommand未成功，添加按钮时出现DataContext不匹配问题，添加SelectedItem后也无法处理事件，附上相关代码寻求技术帮助。

原MainWindow.axaml代码 #

<DockPanel>
    <TreeView DockPanel.Dock="Left" 
              ItemsSource="{Binding BookTree.Genres}">
        <TreeView.DataTemplates>
            <TreeDataTemplate DataType="models:Genre" ItemsSource="{Binding Books}">
                <Border HorizontalAlignment="Left"
                        BorderBrush="Gray" BorderThickness="1"
                        CornerRadius="5" Padding="15 3">
                    <TextBlock Text="{Binding Name}"/>
                </Border>
            </TreeDataTemplate>
            <DataTemplate DataType="models:Book">
                <StackPanel Orientation="Vertical">
                    <TextBlock Text="{Binding Title}"/>
                    <TextBlock Foreground="Red" Text="{Binding Author}"/>
                </StackPanel>
            </DataTemplate>
        </TreeView.DataTemplates>
    </TreeView>

    <DataGrid DockPanel.Dock="Right" ItemsSource="{Binding SelectedBooks.SelectedBooks}">
        <DataGrid.Columns>
            <DataGridTextColumn Header="Title" Binding="{Binding Title}" />
            <DataGridTextColumn Header="Author" Binding="{Binding Author}" />
        </DataGrid.Columns>
    </DataGrid>
</DockPanel>

原MainWindowViewModel.cs代码 #

namespace SummerBooks.ViewModels
{
    public class MainWindowViewModel : ViewModelBase
    {
        public ICommand AddBookCommand { get; }
        public BookTreeViewModel BookTree { get; }
        public SelectedBooksViewModel SelectedBooks { get; }

        public MainWindowViewModel()
        {
            BookTree = new BookTreeViewModel();
            SelectedBooks = new SelectedBooksViewModel();
            AddBookCommand = ReactiveCommand.Create<Book>(book => 
            { 
                SelectedBooks.AddBook(book); 
            });
        }

    }

    public class BookTreeViewModel : ViewModelBase
    {
        public SelectedBooksViewModel SelectedBooks { get; }
        public List<Genre> Genres { get; }

        public BookTreeViewModel()
        {
            Genres = new List<Genre>
            {
                new Genre
                {
                    Name = "Fantastic",
                    Books = new List<Book>
                    {
                        new Book { Title = "1984", Author = "George Orwell"},
                        new Book { Title = "Solaris", Author = "Stanislav Lem"}
                    }
                },

                new Genre
                 {
                    Name = "Horror",
                    Books = new List<Book>
                    {
                        new Book { Title = "Ridges of Madness", Author = "Howard Lovecraft" },
                        new Book { Title = "Dreamcatcher", Author = "Stephen King" }
                    }
                },

                new Genre
                {
                    Name = "Fantasy",
                    Books = new List<Book>
                    {
                        new Book { Title = "Lord of the Rings", Author = "John Tolkien" },
                        new Book { Title = "Harry Potter and the Philosopher's Stone", Author = "Joanne Rowling" }
                    }
                }
            };

        }

    }

    public class SelectedBooksViewModel : ViewModelBase
    {
        public ObservableCollection<Book> SelectedBooks { get; }

        public SelectedBooksViewModel()
        {
            SelectedBooks = new ObservableCollection<Book>();
        }

        public void AddBook(Book book)
        {
            SelectedBooks.Add(book);
            //var box = MessageBoxManager.GetMessageBoxStandard("Caption", $"{SelectedBooks.Count}", MsBox.Avalonia.Enums.ButtonEnum.Ok);
            //box.ShowAsync();
        }
    }

}

核心问题是Book项的DataContext是Book对象，而AddBookCommand位于MainWindowViewModel中，直接绑定会出现DataContext不匹配。解决方法是通过RelativeSource向上查找窗口的DataContext，将双击事件绑定到MainWindowViewModel的AddBookCommand，并传递当前Book作为参数。

修改后的MainWindow.axaml（关键部分） #

修改Book的DataTemplate，给外层StackPanel添加DoubleTapped命令绑定：

<DataTemplate DataType="models:Book">
    <StackPanel Orientation="Vertical"
                DoubleTapped="{Binding DataContext.AddBookCommand, RelativeSource={RelativeSource AncestorType=Window}, CommandParameter={Binding}}">
        <TextBlock Text="{Binding Title}"/>
        <TextBlock Foreground="Red" Text="{Binding Author}"/>
    </StackPanel>
</DataTemplate>

解释 #

• RelativeSource={RelativeSource AncestorType=Window}：向上找到窗口的DataContext（即MainWindowViewModel），以此访问AddBookCommand。
• CommandParameter={Binding}：将当前Book对象作为参数传递给AddBookCommand，与ViewModel中ReactiveCommand.Create<Book>的参数类型完全匹配。

验证逻辑 #

双击左侧TreeView中的任意书籍项，AddBookCommand会被触发，调用SelectedBooks.AddBook(book)将书籍添加到右侧DataGrid的数据源中。由于SelectedBooks是ObservableCollection<Book>，DataGrid会自动更新显示新添加的书籍。

内容的提问来源于stack exchange，提问作者John Smith