Jquery validate onValid

I am using calling a method on the OnValid event, but the values in my form have cleared by the time I try to reference them in my method. Does anybody know what I am doing wrong?

$("form").validate({
         //errorLabelContainer: $("#divErrors"),

             rules: {
                 txtUserName: {
                     required: true,
                     minlength: 4,
                     maxlength: 20
                 },
                 txtPassword: {
                     required: true,
                     minlength: 4,
                     maxlength: 32
                 },
                 txtConfirmPassword: {
                     required: true,
                     equalTo: "#txtPassword",
                     minlength: 4,
                     maxlength: 32
                 },
                 txtFirstName: {
                    required: true,
                    maxlength: 50
                 },
                 txtLastName: {
                    required: true,
                    maxlength: 50
                 },
                 txtJobTitle: {
                    required: true,
                    maxlength: 100
                 },
                 txtEmailAddress: {
                     required: true,
                     email: true,
                     maxlength: 100
                 },
                 txtTelephoneNumber: {
                     required: true,
                     number: true//,
                     //postalCode:true
                 }
             },
             messages: {
                 txtUserName: {
                     required: "Please enter a User Name",
                     minlength: "User Name must be at least 4 characters",
                     maxlength: "User Name must be no more than 20 characters"
                 },
                 txtPassword: {
                     required: "Please enter a Password",
                     minlength: "Password must be at least 4 characters",
                     maxlength: "Password must be no more than 32 characters"
                 },
                 txtConfirmPassword: {
                     required: "Please confirm Password",
                     equalTo: "Confirm Password must match Password",
                     minlength: "Confirm Password must be at least 4 characters",
                     maxlength: "Confirm Password must be no more than 32 characters"
                 },
                 txtFirstName: {
                     required: "Please enter a First Name",
                     maxlength: "First Name must be no more than 50 characters"
                 },
                 txtLastName: {
                     required: "Please enter a Last Name",
                     maxlength: "Last Name must be no more than 50 characters"
                 },
                 txtJobTitle: {
                     required: "Please enter a Job Title",
                     maxlength: "Job Title must be no more than 100 characters"
                 },
                 txtEmailAddress: {
                     required: "Please enter an Email Address",
                     email: "Please enter a valid Email Address",
                     maxlength: "Email Address must be no more than 100 characters"
                 },
                 txtTelephoneNumber: {
                     required: "Please enter a Telephone Number",
                     number: "Telephone Number must be numeric"
                 }
             }
             onValid : function() {
                addUser();
            }
         });
     });

   function addUser() {

       alert($('input[name="txtUserName"]').val());
   }

EDIT :

Many thanks for your help! When you specify a function for submitHandler, can you use it to call a method to for example do additional validation and then calling another method to write to the database? I have specified a method in my submitHandler, but I get the error 'invalid label {"d":0}'. Here is my amended code :

$.validator.setDefaults({
             submitHandler: function() { addUser(); }
         });

function addUser() {

         //check for unique username and email
         $.ajax(
         {
             type: "POST",
             url: "/Services/CDServices.asmx/CheckForUniqueUserName",
             data: "{strUserName:'"开发者_JAVA技巧 + $('input[name="txtUserName"]').val() + "'}",
             async: false,
             dataType: "json",
             contentType: "application/json; charset=utf-8",
             success: function(msg) {
                 if (msg.d == 0) {
                     alert("already exists");
                 }
                 else {
                     alert("username is unique");
                 }
             }
         });

$.validator.setDefaults({
    submitHandler: function() { alert("submitted!"); }
});

$().ready(function() {
    // validate the comment form when it is submitted
    $("#commentForm").validate();
})

From the source of Validate.