Create a bindable property

[mce]

I want to create a bindable property for a button class that is derived from System.Windows.Forms.Button.

  class MyButton : System.Windows.Forms.Button
    {

        public MyButton()
        {

        }
        int _bExternalOn = 0;
   
     
        [System.ComponentModel.Bindable(true)]
        public int ExternalCmd
        {
            set { 
                _bExternalOn = value; 
            }
            get 
            { 
                return _bExternalOn; 
            }
        }

  }

//in form, button1 is an instance of MyButton

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            button1.DataBindings.Add(new Binding("ExternalCmd", testSrc, "SRC_VALUE"));

        }

        Src testSrc = new Src();
        public class Src
        {
            int nVal = 0;
            public int SRC_VALUE
            {
                get { return nVal; }
                set { nVal = value; }
            }
        }

private void button2_Click(object sender, EventArgs e)
        {
            button1.ExternalCmd = 66;//testSrc.SRC_VALUE should show 66 now as this is bind to button1.ExternalCmd , but it doesn;'t. why??

   
        }

}