//允许输入字母、点、回退键、数字
            if (((int)e.KeyChar >= (int)'a' && (int)e.KeyChar <= (int)'z') || (((int)e.KeyChar > 48 && (int)e.KeyChar < 57) || (int)e.KeyChar == 8 || (int)e.KeyChar == 46))
            {
                e.Handled = false;
            }
            else e.Handled = true;



      //允许输入字母、回退键、数字
            if (((int)e.KeyChar >= (int)'a' && (int)e.KeyChar <= (int)'z') || (((int)e.KeyChar > 48 && (int)e.KeyChar < 57) || (int)e.KeyChar == 8))
            {
                e.Handled = false;
            }
            else e.Handled = true; 


// 只能输入字母数字以及中文字
  if ((e.KeyChar != '\b') && (!Char.IsLetter(e.KeyChar)) && (!char.IsDigit(e.KeyChar)))
            {
                e.Handled = true;
            }

//只输入数字
 if (e.KeyChar != 8 && (!Char.IsDigit(e.KeyChar)))
            {
                e.Handled = true;
            }

只能输入数字以及字母X

  if (e.KeyChar != 88 && e.KeyChar != 8 && (!Char.IsDigit(e.KeyChar)))
            {
                e.Handled = true;
            }