c# - 如何检查选择的下拉值是否与数据库值匹配，然后仅激活提交按钮。ASP.NET C#

Question

我想检查用户选择的下拉列表中的下拉值是否与数据库值匹配，然后我只想在表单末尾激活提交按钮。请帮忙。我不知道我应该在这部分代码中输入什么来实现这一点。我已经有了数据库

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = @"Data Source=(localdb)\v11.0;Initial Catalog=facultylog;Integrated Security=True";
    try
    {
        con.Open();
        SqlCommand c = new SqlCommand("Select Username,Password from Log", con);

        SqlDataReader r = c.ExecuteReader();
        while (r.Read())
        {
    **if(DropDownList1.SelectedValue** 
   ????
    }
    catch (Exception)
    { Response.Write("no"); }
    finally { con.Close(); }
}
}
}

标签： c#asp.netwebformsdropdown