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

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace Command
{
    public partial class Form1 : Form
    {
        conection comm = new conection();
        
        public Form1()
        {
            InitializeComponent();
        }
        
        private void Form1_Load(object sender, EventArgs e)
        {
            label1.Text = "Name";//名字
            label2.Text = "Unit";//单位
            label3.Text = "Sex";//性别
            label4.Text = "Age";//年龄
            label5.Text = "Race";//种族
            label6.Text = "Url";//网址
            dataGridView1.DataSource = XianShiShuJu();
        }
        public DataTable XianShiShuJu()
        {
            comm.com().Open();
            DataSet ds = new DataSet("数据集1");
            DataTable dt = new DataTable("数据表1");
            SqlDataAdapter da = new SqlDataAdapter("select * from Staff", comm.com());
            ds.Tables.Add(dt);
            da.Fill(dt);
            comm.com().Close();
            return dt;
        }
        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                string Mycom = "insert Staff(Name,Unit,Sex,Age,Race,Url) values ("" + textBox1.Text + "","" + textBox2.Text + "","" + textBox3.Text + ""," + Convert.ToInt32(textBox4.Text) + ","" + textBox6.Text + "","" + textBox7.Text + """;
                SqlCommand com = new SqlCommand(Mycom, comm.com());
                comm.com().Open();
                using (comm.com())
                {
                    
                    com.ExecuteNonQuery();
                    MessageBox.Show("添加成功","数据保存");
                    textBox1.Clear();
                    textBox2.Clear();
                    textBox3.Clear();
                    textBox4.Clear();
                    textBox6.Clear();
                    textBox7.Clear();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message.ToString());
            }
            comm.com().Close();
        }
        private void button2_Click(object sender, EventArgs e)
        {
            dataGridView1.DataSource = this.XianShiShuJu();
        }   
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
namespace Command
{
    class conection
    {
        public SqlConnection com()
        {
            string Mycon = "server = XQ-20160210KQLE\SA;uid = sa;pwd = 123456;database = JYXinXi";
            SqlConnection con = new SqlConnection(Mycon);
            return con;
        }     
    }
}