C# 在WPF中将画布的派生类添加到窗口时出现问题

我是WPF的新手，我正在学习《职业WPF C#2010》。我想创建一个自定义的canvas派生类，然后将其添加到主窗口中，但无法将其添加到主窗口中

我所做的是创建了一个名为DrawingCanvas的新类（添加了DrawingCanvas.c#file），并声明如下：

<Window x:Class="CustomDrawingCanvas.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <Grid>
        <StackPanel Name="spanel">
            <local:DrawingCanvas x:Name="drawingSurface" Background="White" ClipToBounds="True"
                MouseLeftButtonDown="drawingSurface_MouseLeftButtonDown"
                MouseLeftButtonUp="drawingSurface_MouseLeftButtonUp"
                MouseMove="drawingSurface_MouseMove" />

        </StackPanel>
    </Grid>
</Window>

public void AddDrawingSurface()
    {
        drawingSurface = new DrawingCanvas();
        drawingSurface.Background = new SolidColorBrush(Colors.AliceBlue);
        drawingSurface.ClipToBounds = true;

        Button button = new Button();
        button.Content = "A button";

        //spanel.Children.Add(button);
        spanel.Children.Add(drawingSurface);

    }

类别的定义：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Media;
using System.Windows.Controls;

namespace CustomDrawingCanvas 
{
    public class DrawingCanvas : Canvas
    {
        private List<Visual> visuals = new List<Visual>();

        protected override int VisualChildrenCount
        {
            get
            {
                return visuals.Count;
            }
        }

        protected override Visual GetVisualChild(int index)
       {
            return visuals[index];
        }

        public void AddVisual(Visual visual)
        {
            visuals.Add(visual);
            base.AddVisualChild(visual);
            base.AddLogicalChild(visual);
        }

        public void DeleteVisual(Visual visual)
        {
            visuals.Remove(visual);
            base.RemoveVisualChild(visual);
            base.RemoveLogicalChild(visual);

        }
    }
}

我在InitializeComponent（）之后调用这个函数

---

添加按钮，但不添加堆栈面板。请解释一下我缺少的东西是什么，我尝试过谷歌搜索，并找到了许多通过代码添加自定义元素的方法，方法大体相同，适用于其他元素，但不适用于DrawingCanvas:Canvas类。

您需要在Windows类标题中声明您的本地别名，即

<Window x:Class="CustomDrawingCanvas.MainWindow"  
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
xmlns:local="The namespace of your custom control here"
Title="MainWindow" Height="350" Width="525">  

<Window x:Class="CustomDrawingCanvas.MainWindow"  
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
xmlns:local="The namespace of your custom control here"
Title="MainWindow" Height="350" Width="525">