The ControlToValidate property of 'NameValid' cannot be blank - asp.net

Question

i m writing a web application and i have a problem in one on my pages!
i design a admin page and i want to log in before user enter in this page!
there are three RequiredFieldValidator and a button(AddButton) in my page and i want to check the fields when user click the button but when the page is loaded the validation is checked and visual studio throw a exception:
"The ControlToValidate property of 'NameValid' cannot be blank" NameValid is one of my Validation controls in page!
and another question: what is the advantage of (using) block when you work with databases and files?
my class is here:
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (Request.UrlReferrer == null)
{
//a page for log in
Response.Redirect("~/LogIn.aspx");
}
}
protected void Page_Error(object sender, EventArgs e)
{
Response.Clear();
Response.Write("<h2>Exception</h2><br />");
Response.Write(Server.GetLastError().Message);
Server.ClearError();
}
protected void AddButton_Click(object sender, EventArgs e)
{
const string ConnectionString = #"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\rasoul\sourcecode\ASP-PROJECTS\UniversityDataBase\DataBase\PersonDataBase.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";
using (SqlConnection con=new SqlConnection(ConnectionString))
{
string ID = IDField.Text.Trim();
string Name = NameField.Text.Trim();
string LastName = LastNameField.Text.Trim();
DataSet data = new DataSet();
SqlCommand cmd = con.CreateCommand();
cmd.CommandText = String.Format("insert into StudentTable values('{0}','{1}','{2}')", ID, Name, LastName);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
}
what should i do?

Answer 1

In required field validators you MUST specify the ControlToValidate - the control you which to validate that it is required.
MSDN Description - Use the ControlToValidate property to specify the input control to validate. This property must be set to the ID of an input control for all validation controls except the CustomValidator control, which can be left blank. If you do not specify a valid input control, an exception will be thrown when the page is rendered. (Source: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.basevalidator.controltovalidate.aspx)
The advantage of the using block is it ensures the correct use of IDisposable objects.
using (Font font1 = new Font("Arial", 10.0f))
{
byte charset = font1.GdiCharSet;
}
is equivalent to
{
Font font1 = new Font("Arial", 10.0f);
try
{
byte charset = font1.GdiCharSet;
}
finally
{
if (font1 != null)
((IDisposable)font1).Dispose();
}
}
Source: http://msdn.microsoft.com/en-us/library/yh598w02.aspx

Answer 2

you have to check controltovalidate. you have to assign controller.