Connection 属性尚未在 ASP.NET 中初始化

问：

dbconnection con = new dbconnection();
string usermail = txtboxmail.Text;
string userpass = txtpassword.Text;

string query = "SELECT * FROM Admin_Login where Email='" + usermail + "', Password='" + userpass + "'";

SqlCommand cmd = new SqlCommand(query);
SqlDataReader sdr = cmd.ExecuteReader();

if (sdr.Read())
{
    Response.Write("<script>alert('Login Success')</script>");
}
else
{
    Response.Write("<script>alert('Something Went Wrong')</script>");
}

我正在尝试创建一个登录页面，当我运行该页面时，它显示标题中提到的错误。