ExecuteNonQuery 要求已打开且可用的连接。连接的当前状态为已关闭

Question

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;public partial class Register : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {    }
    protected int isName()
    {
        int i;
        String name = TextBox1.Text;
        if (name.Trim() != "")
        {
            SqlConnection con = new SqlConnection("server=Mumble;database=hibar;Integrated Security=True;");
            SqlCommand cmd = new SqlCommand("select count(*) from guest where adminName ='" + name + "'", con);
            return i = Convert.ToInt32(cmd.ExecuteNonQuery());
            con.Close();
        }
        else
        {
            return 1;
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        int i = isName();
        if (i <= 0)
        {
            if (add())
            {
                SqlConnection con = new SqlConnection("server=Mumble;database=hibar;Integrated Security=True;");
                con.Open();
                SqlCommand cmd = new SqlCommand("insert guest(adminName,adminPwd) values('"+TextBox1.Text + "','" + TextBox2.Text +"')",con);
                cmd.ExecuteNonQuery();
                Response.Write("<script>alert('注册成功！');location='Default.aspx';</script>");
                con.Close();
            }
            else
            {
                Response.Write("<script>alert('注册失败')</script>");
            }
        }
        else
        {
            Response.Write("<script>alert('用户名已存在')</script>");
        }
    }
    public bool add()
    {
        string pass = FormsAuthentication.HashPasswordForStoringInConfigFile(TextBox2.Text,"MD5");
        string sex;
        string Birthday = DropDownList1.SelectedValue + '.' + DropDownList2.SelectedValue + '.' + DropDownList3.SelectedValue;
        if(rbMan.Checked)
        {
            sex ="男";
        }
        else
        {
            sex = "女";
        }
        string sql = "insert into Login_Info(Name,Pass,Sex,Email,Birthday) values('" + TextBox1.Text.Trim() + "','" + pass +"','" + sex +"','" + TextBox4.Text.Trim() + "','" + Birthday + "')";
        SqlConnection con = new SqlConnection("server=Mumble;database=hibar;Integrated Security=True;");
        con.Open();
        SqlCommand cmd = new SqlCommand(sql,con);
        int i = Convert.ToInt32(cmd.ExecuteNonQuery());
        con.Close();
        if (i>0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

Answer 1

usign(SqlConnection con = new SqlConnection("server=Mumble;database=hibar;Integrated Security=True;"))
{
con.Open();}