Error submitting form data using knockout and mvc - knockout-mvc

Question

#model NewDemoApp.Models.DemoViewModel
#{
ViewBag.Title = "Home Page";
}
#*<script src="#Url.Content("~/Scripts/jquery-1.9.1.min.js")" type="text/javascript"></script>*#
<script src="http://code.jquery.com/jquery-1.11.3.min.js"></script>
<script src="http://code.jquery.com/jquery-migrate-1.2.1.min.js"></script>
<script src="#Url.Content("~/Scripts/knockout-3.3.0.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
<script type="text/javascript">
var viewModel;
var compViewModel, userViewModel;
$(document).ready(function () {
$(".wizard-step:visible").hide();
$(".wizard-step:first").show(); // show first step
$("#back-step").hide();
var result = #Html.Raw(Json.Encode(Model));
var viewModel = new DemoViewModel(result.userViewModel);
//viewModel.userViewModel.FirstName = result.userViewModel.FirstName;
//viewModel.userViewModel.LastName = result.userViewModel.LastName;
//viewModel.userViewModel.State = result.userViewModel.State;
//viewModel.userViewModel.City = result.userViewModel.City;
ko.applyBindings(viewModel);
});
var userVM = function(){
FirstName = ko.observable(),
LastName = ko.observable(),
State = ko.observable(),
City = ko.observable()
};
function DemoViewModel(data) {
var self = this;
self.userViewModel = function UserViewModel(data) {
userVM.FirstName = data.FirstName;
userVM.LastName = data.LastName;
userVM.State = data.State;
userVM.City = data.City;
}
self.Next = function () {
var $step = $(".wizard-step:visible"); // get current step
var form = $("#myFrm");
var validator = $("#myFrm").validate(); // obtain validator
var anyError = false;
$step.find("input").each(function () {
if (!validator.element(this)) { // validate every input element inside this step
anyError = true;
}
});
if (anyError)
return false; // exit if any error found
if ($step.next().hasClass("confirm")) { // is it confirmation?
$step.hide().prev(); // hide the current step
$step.next().show(); // show the next step
$("#back-step").show();
$("#next-step").hide();
//$("#myFrm").submit();
// show confirmation asynchronously
//$.post("/wizard/confirm", $("#myFrm").serialize(), function (r) {
// // inject response in confirmation step
// $(".wizard-step.confirm").html(r);
//});
}
else {
if ($step.next().hasClass("wizard-step")) { // is there any next step?
$step.hide().next().fadeIn(); // show it and hide current step
$("#back-step").show(); // recall to show backStep button
$("#next-step").show();
}
}
}
self.Back = function () {
var $step = $(".wizard-step:visible"); // get current step
if ($step.prev().hasClass("wizard-step")) { // is there any previous step?
$step.hide().prev().fadeIn(); // show it and hide current step
// disable backstep button?
if (!$step.prev().prev().hasClass("wizard-step")) {
$("#back-step").hide();
$("#next-step").show();
}
else {
$("#back-step").show();
$("#next-step").show();
}
}
}
self.SubmitForm = function (formElement) {
$.ajax({
url: '#Url.Content("~/Complaint/Save")',
type: "POST",
data: ko.toJS(self),
done: function (result) {
var newDiv = $(document.createElement("div"));
newDiv.html(result);
},
fail: function (err) {
alert(err);
},
always: function (data) {
alert(data);
}
});
}
self.loadData = function () {
$.get({
url: '#Url.Content("~/Complaint/ViewComplaint")',
done: function (data) {
debugger;
alert(data);
self.compViewModel(data);
self.userViewModel(data);
},
fail: function (err) {
debugger;
alert(err);
},
always: function (data) {
debugger;
alert(data);
}
});
}
}
</script>
<form class="form-horizontal" role="form" id="myFrm">
<div class="container">
<div class="row">
<div class="col-md-3">
</div>
<div class="col-md-6">
<div class="wizard-step">
</div>
<div class="wizard-step" >
<h3> Step 2</h3>
#Html.Partial("UserView", Model.userViewModel)
<div class="col-md-3"></div>
<div class="col-md-6">
<input type="submit" id="submitButton" class="btn btn-default btn-success" value="Submit" data-bind="click: SubmitForm" />
</div>
<div class="col-md-3"></div>
</div>
<div class="wizard-step">
<h3> Step 3</h3>
</div>
<div class="wizard-step confirm">
<h3> Final Step 4</h3>
</div>
</div>
<div class="col-md-3"></div>
</div>
<div class="row">
<div class="col-md-3"></div>
<div class="col-md-6">
<input type="button" id="back-step" class="btn btn-default btn-success" value="< Back" data-bind="click: Back" />
<input type="button" id="next-step" class="btn btn-default btn-success" value="Next >" data-bind="click: Next" />
</div>
<div class="col-md-3"></div>
</div>
</div>
</form>
I am able to get the data from controller and bind it using knockout. There is a partial view that loads data from controller. But when submitting the updated data, I do not get the data that was updated, instead getting error that "FirstName" property could not be accessed from null reference. I just need to get pointers where I am going wrong especially the right way to create ViewModels and use them.

Answer 1

When you are submitting the form in self.SubmitForm function you are passing Json object which is converted from Knockout view model.
So make sure you are providing the data-bind attributes in all input tags properly. If you are using Razor syntax then use data_bind in Html attributes of input tags.
Check 2-way binding of KO is working fine. I can't be sure as you have not shared your partial view Razor code.
Refer-
http://knockoutjs.com/documentation/value-binding.html
In Chrome you can see what data you are submitting in Network tab of javascript developer console. The Json data that you are posting and ViewModel data structure you are expecting in controller method should match.
You can also change the parameters to expect FormCollection formCollection and check what data is coming from browser when you are posting.