使用DispatcherHelper类执行对话框操作。

示例如下：

using Avalonia;
using Avalonia.Controls;
using Avalonia.Threading;
using ReactiveUI;

public class MainWindowViewModel : ReactiveObject
{
    public ReactiveCommand SelectFolderCommand { get; }

    public MainWindowViewModel()
    {
        SelectFolderCommand = ReactiveCommand.CreateFromTask(SelectFolder);
    }

    private async Task SelectFolder()
    {
        var dialog = new OpenFolderDialog();
        
        // 使用DispatcherHelper类执行对话框操作
        var result = await Dispatcher.UIThread.InvokeAsync(() => dialog.ShowAsync(App.GetCurrentWindow()));
        
        if (result != null)
        {
            // 处理选择的文件夹
        }
    }
}