只接受ASCII字符的TextBox

using System;
using System.Windows.Forms;

namespace ControlLibrary
{
    public class AsciiTextBox : TextBox
    {

        //消息
        private int WM_CHAR = 0x0102;

        protected override void WndProc(ref Message m)
        {

            //条件判断
            if (m.Msg == WM_CHAR && m.WParam.ToInt32() > 127)
                return;
            base.WndProc(ref m);
        }
    }
}