如何通过VisualCollection在Canvas上绘制？

问题描述

目标：通过VisualCollection在Canvas上绘制。

问题：它使用Window。

问题：如何解决？ Visual Parent的含义是什么？

描述：我通过Canvas实例创建一个VisualCollection实例作为Visual Parent，但它在Window上绘制，尽管我从未将它作为内容添加到Window。

那么，如果它仍然使用Window，Visual Parent意味着什么？换句话说，我想在图像或画布上绘制并保存它，但不是在窗口上，我不想显示我绘制的内容。

代码：

Goal: To draw on Canvas by VisualCollection.
Problem: It draws on Window.
Question: How to solve? What does Visual Parent means?
Description: I create a VisualCollection instance by a Canvas instance as Visual Parent, but it draws on Window despite the fact i never added it to Window as content.
So what does Visual Parent means if it still draws on Window? In other words i wanna draw on Image or Canvas and save it, but not on Window, i don't wanna show what i draw.
Code:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        Canvas canvas = new Canvas();
        vc = new VisualCollection(canvas);
        this.Loaded += MainWindow_Loaded;
    }

    VisualCollection vc;

    void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        DrawingVisual dv = new DrawingVisual();
        DrawingContext dc = dv.RenderOpen();

        dc.DrawRectangle(Brushes.Red, new Pen(Brushes.Red, 5), new Rect(10, 10, 100, 100));
        dc.Close();

        vc.Add(dv);
    }

    protected override Visual GetVisualChild(int index)
    {
        return vc[index];
    }
    protected override int VisualChildrenCount
    {
        get { return vc.Count; }
    }
}

推荐答案

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        canvas = new Canvas();
        canvas.Width = 300;
        canvas.Height = 300;
        this.Content = canvas;
        this.Loaded += MainWindow_Loaded;
    }

    Canvas canvas;

    void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        DrawingVisual dv = new DrawingVisual();
        DrawingContext dc = dv.RenderOpen();

        dc.DrawRectangle(Brushes.Red, new Pen(Brushes.Red, 5), new Rect(10, 10, 100, 100));
        dc.Close();

        RenderTargetBitmap bmp = new RenderTargetBitmap(180, 180, 0, 0, PixelFormats.Pbgra32);
        bmp.Render(dv);

        Image image = new Image();
        image.Source = bmp;

        canvas.Children.Add(image);
    }
}

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