How to programing for control user-defined attribute?

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C#3.5

I use VS2010 "Windows Forms Control Libray" to create user control, but i'm in troubles, i can't input any value to control attribute. the sample code as follow:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace ChartTest
{
    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }

        public class CMyClass
        {
            private int x;
            private int y;

            public int X
            {
                set
                {
                    x = value;
                }
                get
                {
                    return x;
                }
            }

            public int Y
            {
                set
                {
                    y = value;
                }
                get
                {
                    return y;
                }
            }
        }

        private CMyClass mc = new CMyClass();

        public CMyClass MC
        {
            set
            {
                mc = value;
            }
            get
            {
                return mc;
            }
        }
    }
}

i can set focus to control attribute editor, but i can't to input any value. i'm a newcomes, can you guide me to solve this question? thanks a lot.