C# Winform限制文本框输入数字+字母+长度

        private void txtFTrayCode_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar >= '0' && e.KeyChar <= '8'|| Char.IsLetter(e.KeyChar))//输入1-8位数字或字母
            {
                if (txtFTrayCode.Text.Length <= 7)
                {
                    e.Handled = false;    
                }
                else if (txtFTrayCode.SelectionLength > 1)
                {
                    e.Handled = false;//选择多个
                }
                else
                {
                    e.Handled = true;
                }
            }
            else if (e.KeyChar == '.' || e.KeyChar == (char)Keys.Return) //Tab或回车键
            {
                e.Handled = true;
                SendKeys.Send("{TAB}");
            }
            else if (e.KeyChar == '\b' || (int)e.KeyChar == 7)
                e.Handled = false;//删除
            else
                e.Handled = true;
        }