Page.IsValid not working

Question

hello,

 

i m validating page on button_click event and transferinf data to database. Even though valueus in text box is null(blank) Page.IsValid property returns true and blank data loaded to database. i tried CausesValidation ="true" also. but does not work.please resolve .

 

CODE behind is 

protected void btnRegister_Click(object sender, EventArgs e)
{
if (Page.IsValid)
{
// Read the connection string from web.config.
// ConfigurationManager class is in System.Configuration namespace
string CS = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
// SqlConnection is in System.Data.SqlClient namespace
using (SqlConnection con = new SqlConnection(CS))
{
SqlCommand cmd = new SqlCommand("spRegisterUser", con);
cmd.CommandType = CommandType.StoredProcedure;
SqlParameter username = new SqlParameter("@UserName", txtUserName.Text);
// FormsAuthentication calss is in System.Web.Security namespace
string encryptedPassword = FormsAuthentication.
HashPasswordForStoringInConfigFile(txtPassword.Text, "SHA1");
SqlParameter password = new SqlParameter("@Password", encryptedPassword);
SqlParameter email = new SqlParameter("@Email", txtEmail.Text);
cmd.Parameters.Add(username);
cmd.Parameters.Add(password);
cmd.Parameters.Add(email);
con.Open();
int ReturnCode = (int)cmd.ExecuteScalar();
if (ReturnCode == -1)
{
lblMessage.Text = "User Name already in use, please choose another user name";
lblMessage.ForeColor = System.Drawing.Color.Red;
}
else
{
Response.Redirect("~/Login.aspx");
}
}
}
}

SQL Table and Stored Procedure 

Create table tblUser
(
[Id] int Primary Key Identity not null,
[UserName] nvarchar(100) not null,
[Mobile No] int not null,
[Email] nvarchar (100) not null,
[Password] nvarchar(max) not null
)
Select * From tblUser
CREATE PROC [dbo].[spRegisterUser]
@UserName NVARCHAR(100),
@MobileNo int,
@Email NVARCHAR(100),
@Password nvarchar (max)
AS
BEGIN
DECLARE @Count INT
DECLARE @ReturnCode INT
SELECT @Count = COUNT(userName)
FROM tblUser
WHERE userName = @UserName
IF @Count > 0
BEGIN
SET @ReturnCode = - 1
END
ELSE
BEGIN
SET @ReturnCode = 1
INSERT INTO tblUser VALUES
(@UserName,@MobileNo,@Email,@Password)
END
SELECT @ReturnCode AS ReturnValue
END