C#在属性窗口中展示如Size一样的对象

1.效果图 

2.对象和控件

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

namespace AttributeTest
{
    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
            this.BackColor = Color.Yellow;
        }

        public AB AAA { get; set; } = new AB { A = "2", B = "3" };
    }

    [TypeConverter(typeof(ABConverter))]
    public class AB
    {
        public string A { get; set; }
        public string B { get; set; }
    }

}

3.类型转换器 

using System;
using System.Collections;
using System.ComponentModel;
using System.ComponentModel.Design.Serialization;
using System.Globalization;
using System.Reflection;

namespace AttributeTest
{
    public class ABConverter: TypeConverter 
    {
        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
        {
            if (sourceType == typeof(string))
            {
                return true;
            }
            return base.CanConvertFrom(context, sourceType);
        }

        public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
        {
            if (destinationType == typeof(string))
            {
                return true;
            }
            if (destinationType == typeof(InstanceDescriptor))
            {
                return true;
            }
            return base.CanConvertTo(context, destinationType);
        }

        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
        {
            if (value == null)
            {
                return base.ConvertFrom(context, culture, value);
            }
            string s = value as string;
            string[] ps = s.Split(',');
            if (ps.Length != 2)
            {
                throw new ArgumentException("error!");
            }
            return new AB() { A = ps[0], B = ps[1] };
        }

        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
        {
            if (destinationType == typeof(string) && value is AB)
            {
                AB a = (AB)value;
                return string.Format("A={0},B={1}", a.A, a.B);
            }
            if (destinationType == typeof(InstanceDescriptor) && value is AB)
            {
                AB vd = (AB)value;
                ConstructorInfo ctor = typeof(AB).GetConstructor(new Type[] { typeof(string), typeof(string) });
                return new InstanceDescriptor(ctor, new object[] { vd.A, vd.B });
            }
            return base.ConvertTo(context, culture, value, destinationType);
        }

        /// <summary>
        /// 改变数值时重新生成对象
        /// </summary>
        /// <param name="context"></param>
        /// <param name="propertyValues"></param>
        /// <returns></returns>
        public override object CreateInstance(ITypeDescriptorContext context, IDictionary propertyValues)
        {
            string aa = propertyValues["A"].ToString();
            string bb = propertyValues["B"].ToString();
            return new AB() { A = aa, B = bb };
        }

        /// <summary>
        /// 显示属性集合时要以怎样的形式
        /// </summary>
        /// <param name="context"></param>
        /// <param name="value"></param>
        /// <param name="attributes"></param>
        /// <returns></returns>
        public override PropertyDescriptorCollection GetProperties(ITypeDescriptorContext context, object value, Attribute[] attributes)
        {
            if (value is AB)
            {
                return TypeDescriptor.GetProperties(value, attributes);
            }
            return base.GetProperties(context, value, attributes);
        }

        public override bool GetCreateInstanceSupported(ITypeDescriptorContext context)
        {
            return true;
        }

        public override bool GetPropertiesSupported(ITypeDescriptorContext context)
        {
            return true;
        }

    }
}