对象引用未设置为对象asp.net的实例

我有两个问题：

1. 我如何用其他方式使用textbox，这样它就不会抛出任何错误
2. 我得到一个错误：
   

   "对象引用未设置为对象的实例。

我不知道该怎么修。有人能看一下吗？

protected void DataGridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName.Equals("InsertFooter"))
        {

            try
            {
                System.Web.UI.WebControls.TextBox txtEmp_num = (System.Web.UI.WebControls.TextBox)DataGridView1.Controls[0].Controls[0].FindControl("txtEmp_num");
                System.Web.UI.WebControls.TextBox txtEmp_fn = (System.Web.UI.WebControls.TextBox)DataGridView1.Controls[0].Controls[0].FindControl("txtEmp_fn");
                System.Web.UI.WebControls.TextBox txtEmp_ln = (System.Web.UI.WebControls.TextBox)DataGridView1.Controls[0].Controls[0].FindControl("txtEmp_ln");
                System.Web.UI.WebControls.TextBox txtEmp_phone = (System.Web.UI.WebControls.TextBox)DataGridView1.Controls[0].Controls[0].FindControl("txtEmp_phone");
                System.Web.UI.WebControls.TextBox txtEmp_email = (System.Web.UI.WebControls.TextBox)DataGridView1.Controls[0].Controls[0].FindControl("txtEmp_email");
                MySqlConnection conn = new MySqlConnection(connection);
                MySqlCommand cmd = new MySqlCommand();
                cmd.Connection = conn;
                cmd.CommandText = "insert into employees(Emp_number,First_name,Last_name,Phone_num,Email) values(@1,@2,@3,@4,@5)";

                cmd.Parameters.AddWithValue("@1", txtEmp_num.Text);
                cmd.Parameters.AddWithValue("@2", txtEmp_fn.Text);
                cmd.Parameters.AddWithValue("@3", txtEmp_ln.Text);
                cmd.Parameters.AddWithValue("@4", txtEmp_phone.Text);
                cmd.Parameters.AddWithValue("@5", txtEmp_email.Text);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
                Bind();

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }