使用DelegateCommand打开文件选择器时，WindowNative.GetWindowHandle抛出无效转换异常

WindowNative.GetWindowHandle(this)抛出“指定的转换无效”异常，核心原因是该方法要求传入WinUI 3的Window对象实例，但你传入的是MainViewModel实例——ViewModel和Window属于完全不同的类型，类型转换失败导致异常。

以下是几种可行的修复方式，按MVVM耦合度从低到高排序：

方案1：封装窗口句柄服务（最符合MVVM） #

创建一个获取窗口句柄的服务接口，解耦ViewModel和Window：

public interface IWindowHandleService
{
    IntPtr GetCurrentWindowHandle();
}

public class WindowHandleService : IWindowHandleService
{
    public IntPtr GetCurrentWindowHandle()
    {
        var currentWindow = Application.Windows.OfType<Window>().FirstOrDefault(w => w.Activated);
        if (currentWindow == null)
            throw new InvalidOperationException("No active window found");
        
        return WindowNative.GetWindowHandle(currentWindow);
    }
}

在ViewModel中注入该服务：

private readonly IWindowHandleService _windowHandleService;

public MainViewModel(IWindowHandleService windowHandleService)
{
    _windowHandleService = windowHandleService;
    OpenFileDialog = new DelegateCommand(browseFileButton_Click, OnMyCommandCanExecute);
}

private async void browseFileButton_Click(object sender)
{
    var filePicker = new FileOpenPicker()
    {
        FileTypeFilter = { ".pdf" },
        ViewMode = PickerViewMode.Thumbnail
    };
    var hWnd = _windowHandleService.GetCurrentWindowHandle();
    InitializeWithWindow.Initialize(filePicker, hWnd);

    var file = await filePicker.PickSingleFileAsync();

    if (file != null)
    {
        ConfigFile = file.Name;
    }
}

最后在应用启动时注册服务（比如App.xaml.cs）：

public App()
{
    InitializeComponent();
    // 注册服务，实际项目可使用依赖注入容器管理
    Services.AddSingleton<IWindowHandleService, WindowHandleService>();
}

方案2：通过构造函数传递Window实例 #

直接在ViewModel构造函数中接收Window实例，保存后使用：
修改ViewModel：

private readonly Window _window;

public MainViewModel(Window window)
{
    _window = window;
    OpenFileDialog = new DelegateCommand(browseFileButton_Click, OnMyCommandCanExecute);
}

private async void browseFileButton_Click(object sender)
{
    var filePicker = new FileOpenPicker()
    {
        FileTypeFilter = { ".pdf" },
        ViewMode = PickerViewMode.Thumbnail
    };
    var hWnd = WindowNative.GetWindowHandle(_window);
    InitializeWithWindow.Initialize(filePicker, hWnd);

    var file = await filePicker.PickSingleFileAsync();

    if (file != null)
    {
        ConfigFile = file.Name;
    }
}

在窗口代码后台（MainWindow.xaml.cs）实例化ViewModel时传入自身：

public MainWindow()
{
    InitializeComponent();
    DataContext = new MainViewModel(this);
}

方案3：通过CommandParameter传递Window #

在XAML按钮绑定中，将Window实例作为命令参数传递：
首先给Window设置x:Name：

<Window x:Class="YourAppNamespace.MainWindow"
        x:Name="RootWindow"
        ...>

然后修改按钮绑定：

<Button Content="Open PDF" 
        Command="{Binding OpenFileDialog}" 
        CommandParameter="{Binding ElementName=RootWindow}" />

最后在ViewModel的命令处理方法中接收参数：

private async void browseFileButton_Click(object parameter)
{
    var window = parameter as Window;
    if (window == null) return;

    var filePicker = new FileOpenPicker()
    {
        FileTypeFilter = { ".pdf" },
        ViewMode = PickerViewMode.Thumbnail
    };
    var hWnd = WindowNative.GetWindowHandle(window);
    InitializeWithWindow.Initialize(filePicker, hWnd);

    var file = await filePicker.PickSingleFileAsync();

    if (file != null)
    {
        ConfigFile = file.Name;
    }
}

内容的提问来源于stack exchange，提问作者Brad