目标为x64时，从工具箱中删除了“自定义组合框”，在任何CPU上均可正常工作

Question

Windows 10 1803 x64 Build 17134.165， Visual Studio 2017 15.7.5 c＃

我在表单上有一个自定义组合框。如果我构建针对任何CPU的解决方案，那没有问题，但是如果我将目标更改为x64，则在设计器中会出现此错误，并且组合框将从工具箱中删除。 designer.cs中的代码完整无缺，程序仍然可以正常运行。

Could not find type 'TestCustomComboBox.ComboBoxCustom'.  Please make sure that the assembly that contains this type is referenced.  If this type is a part of your development project, make sure that the project has been successfully built using settings for your current platform or Any CPU.

如果我恢复为Any CPU，则错误消失，并且组合框又回到了工具箱中。我的电脑是x64。

完整的测试程序：

using System.Drawing;
using System.Windows.Forms;

namespace TestCustomComboBox
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
    }
    /// <summary>
    /// Custom combobox with colour coding
    /// </summary>
    public class ComboBoxCustom : ComboBox
    {
        public ComboBoxCustom()
        {
            this.DrawMode = DrawMode.OwnerDrawFixed;
        }
        protected override void OnDrawItem(DrawItemEventArgs e)
        {
            base.OnDrawItem(e);
            e.DrawBackground();
            var item = (ComboBoxItem)Items[e.Index];
            Brush brush = new SolidBrush(item.ForeColor);
            if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
            { brush = Brushes.Yellow; }
            e.Graphics.DrawString(item.Text, this.Font, brush, e.Bounds.X, e.Bounds.Y);
        }
    }

    public class ComboBoxItem
    {
        public ComboBoxItem() { }

        public ComboBoxItem(string pText, object pValue)
        {
            text = pText; val = pValue;
        }

        public ComboBoxItem(string pText, object pValue, Color pColor)
        {
            text = pText; val = pValue; foreColor = pColor;
        }

        string text = "";
        public string Text
        {
            get { return text; }
            set { text = value; }
        }

        object val;
        public object Value
        {
            get { return val; }
            set { val = value; }
        }

        Color foreColor = Color.Black;
        public Color ForeColor
        {
            get { return foreColor; }
            set { foreColor = value; }
        }

        public override string ToString()
        {
            return text;
        }
    }

    public class ComboObject
    {
        public string DisplayMembers;
        public int ValueMembers;
        public int argb;
        public ComboObject(string theDisplayMembers, int theValueMembers, int theArgb)
        {
            DisplayMembers = theDisplayMembers;
            ValueMembers = theValueMembers;
            argb = theArgb;
        }
        public override string ToString()
        {
            return DisplayMembers;
        }
    }
}