WinUI应用设置RequestedTheme为Dark时打印预览窗口显示空白求助

我在WinUI应用中实现了打印功能，并将RequestedTheme设置为Dark。但使用深色主题时，打印预览窗口无法显示任何文本；切换为Light主题时，文本显示正常。

打印功能源码 #

public sealed partial class MainWindow : Window
{
    private PrintDocument _printDoc;
    private IPrintDocumentSource _printSource;
    private List<UIElement> _pages = new List<UIElement>();
    public MainWindow()
    {
        InitializeComponent();

        _printDoc = new PrintDocument();
        _printSource = _printDoc.DocumentSource;

        _printDoc.Paginate += OnPaginate;
        _printDoc.GetPreviewPage += OnGetPreviewPage;
        _printDoc.AddPages += OnAddPages;
    }

    private async void OnPrintClick(object sender, RoutedEventArgs e)
    {
        var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(this);
        var printManager = PrintManagerInterop.GetForWindow(hWnd);
        printManager.PrintTaskRequested += (s, args) =>
        {
            args.Request.CreatePrintTask("Print Test", t => t.SetSource(_printSource));
        };
        await PrintManagerInterop.ShowPrintUIForWindowAsync(hWnd);
    }

    private void OnPaginate(object sender, PaginateEventArgs e)
    {
        _pages.Clear();
        var page = new StackPanel { Margin = new Thickness(20) };
        page.Children.Add(new TextBlock { Text = "Hello, this is a print test!", FontSize = 24 });
        _pages.Add(page);
        _printDoc.SetPreviewPage(1, page);
    }

    private void OnGetPreviewPage(object sender, GetPreviewPageEventArgs e)
    {
        _printDoc.SetPreviewPage(e.PageNumber, _pages[e.PageNumber - 1]);
    }

    private void OnAddPages(object sender, AddPagesEventArgs e)
    {
        foreach (var p in _pages) _printDoc.AddPage(p);
        _printDoc.AddPagesComplete();
    }
}

深色主题设置代码 #

public partial class App : Application
{
    private Window? _window;

    /// <summary>
    /// Initializes the singleton application object.  This is the first line of authored code
    /// executed, and as such is the logical equivalent of main() or WinMain().
    /// </summary>
    public App()
    {
        this.RequestedTheme = ApplicationTheme.Dark;
        InitializeComponent();
    }
}

效果对比 #

• 深色主题：打印预览窗口无文本显示
• 浅色主题：文本显示正常

解决方法 #

问题根源是打印预览窗口的背景在深色主题下为深色，而动态创建的TextBlock继承了应用深色主题的白色前景色，导致文本与背景对比度为0，无法看见。以下两种方案可解决：

方案1：显式设置文本前景色 #

创建TextBlock时直接指定前景色为黑色（或其他高对比度颜色）：

page.Children.Add(new TextBlock { 
    Text = "Hello, this is a print test!", 
    FontSize = 24,
    Foreground = new SolidColorBrush(Colors.Black)
});

方案2：强制打印页面使用浅色主题 #

为打印用的StackPanel单独设置浅色主题，脱离应用主题影响：

var page = new StackPanel { 
    Margin = new Thickness(20),
    RequestedTheme = ElementTheme.Light
};

两种方案都能确保打印预览及实际打印的内容正常显示。

内容的提问来源于stack exchange，提问作者Swetha