基于VisualBrush实现WPF窗口缩略图的技术问询（附用户控件XAML）

Alright, let's walk through how to use VisualBrush to generate window thumbnails for your existing WPF user control. I'll integrate this with the XAML snippet you shared so it fits right into your current setup.

Core Concept #

VisualBrush lets you take any WPF Visual (like the content of another window) and use it as a brush to paint an element in your control. This is perfect for creating live-updating thumbnails because it automatically reflects changes to the source visual.

Step 1: Update Your XAML Structure #

First, modify your existing Border to use a VisualBrush instead of a solid white background. We'll bind the brush's Visual property to the target window's content (or the window itself if you want the title bar included). Here's how to adjust your code:

<Grid x:Name="containerGrid" Margin="0">
    <Border x:Name="thumbnailBorder" Background="White" CornerRadius="5">
        <!-- Replace solid background with VisualBrush -->
        <Border.Background>
            <VisualBrush x:Name="windowThumbnailBrush" Stretch="Uniform" />
        </Border.Background>
        
        <Border.Style>
            <Style>
                <Style.Triggers>
                    <Trigger Property="Border.IsMouseOver" Value="True">
                        <Setter Property="Border.Effect">
                            <Setter.Value>
                                <DropShadowEffect BlurRadius="20" Color="White" ShadowDepth="0" />
                            </Setter.Value>
                        </Setter>
                    </Trigger>
                </Style.Triggers>
            </Style>
        </Border.Style>
    </Border>
</Grid>

Step 2: Wire Up the Target Window in Code-Behind #

Next, you need to set the Visual property of the VisualBrush to the window you want to display. You can do this in your user control's constructor, or via a dependency property if you want to bind it dynamically.

Basic Implementation (Code-Behind) #

public partial class WindowThumbnailControl : UserControl
{
    // Optional: Dependency property to bind the target window dynamically
    public static readonly DependencyProperty TargetWindowProperty =
        DependencyProperty.Register(nameof(TargetWindow), typeof(Window), typeof(WindowThumbnailControl),
            new PropertyMetadata(null, OnTargetWindowChanged));

    public Window TargetWindow
    {
        get => (Window)GetValue(TargetWindowProperty);
        set => SetValue(TargetWindowProperty, value);
    }

    public WindowThumbnailControl()
    {
        InitializeComponent();
    }

    private static void OnTargetWindowChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (WindowThumbnailControl)d;
        var newWindow = e.NewValue as Window;
        
        if (newWindow != null)
        {
            // Use newWindow.Content to exclude the title bar, or newWindow itself to include it
            control.windowThumbnailBrush.Visual = newWindow.Content;
            
            // Refresh the brush when the target window's layout changes (e.g., resizing)
            newWindow.LayoutUpdated += (s, args) => control.windowThumbnailBrush.Redraw();
        }
        else
        {
            // Reset to white background if no window is set
            control.windowThumbnailBrush.Visual = null;
            control.thumbnailBorder.Background = Brushes.White;
        }
    }
}

Step 3: Handle Edge Cases #

• Window Minimization: If the target window is minimized, the Visual might not render properly. Add a trigger to show a placeholder image/text when the window's WindowState is Minimized.
• Performance: For large windows, VisualBrush can be resource-heavy. If you don't need real-time updates, consider using RenderTargetBitmap for static snapshots instead.
• Stretch Behavior: Adjust the Stretch property of VisualBrush (e.g., Uniform, UniformToFill, Fill) to control how the thumbnail fits your border.

Using the Control #

To use your control, just bind the TargetWindow property to the window you want to display:

<local:WindowThumbnailControl TargetWindow="{Binding YourTargetWindowInstance}" />

This will keep the thumbnail in sync with the target window's content, while retaining your original mouse-over shadow effect.

内容的提问来源于stack exchange，提问作者Fishman