Load tabs with Ajax - asp.net-mvc

Question

I have a bootstrap nav-tab and I want to display dynamically content when I select a tab. Each tab must display a div with some text that is returned from ajax call at the controller's action GetSection().
<div class="tabbable">
<ul class="nav nav-tabs" data-bind="foreach: sections">
<li data-bind="css: { active: isSelected }">
<a href="#" data-bind="click: $parent.selectedSection">
<span data-bind="text: name" />
</a>
</li>
</ul>
<div class="tab-content" data-bind="foreach: sections">
<div class="tab-pane" data-bind="css: { active: isSelected }">
<span data-bind="text: 'In section: ' + retValue" />
</div>
</div>
</div>
Javascript code:
var Section = function (name, selected) {
this.name = name;
this.retValue = "";
this.isSelected = ko.computed(function () {
return this === selected();
}, this);
}
var ViewModel = function () {
var self = this;
self.selectedSection = ko.observable();
self.sections = ko.observableArray([
new Section('Tab One', self.selectedSection),
new Section('Tab Two', self.selectedSection),
new Section('Tab Three', self.selectedSection)
]);
self.selectedSection(self.sections()[0]);
self.selectedSection.subscribe(function () {
$.ajax({
url: '#Url.Action("GetSection")',
data: { name: self.selectedSection().name },
type: 'GET',
success: function (data) {
self.selectedSection().retValue=data.text;
}
});
});
}
ko.applyBindings(new ViewModel());
The problem is that retValue from ajax is not displayed. The controller action is this:
public JsonResult GetSection(string name)
{
var ret = new { text = name + "abcd" };
return Json(ret, JsonRequestBehavior.AllowGet);
}

Answer 1

Knockout can only know to update the view for properties that are obsverable (hence the name), so you need to make retValue observable:
var Section = function (name, selected) {
this.name = name; // <-- consider similar change here too
this.retValue = ko.observable(""); // <-- change here
this.isSelected = ko.computed(function () {
return this === selected();
}, this);
}
Then, you need to remember to set an obsverable's value by calling it as a method with the new value as its only argument, e.g.:
$.ajax({
url: '#Url.Action("GetSection")',
data: { name: self.selectedSection().name },
type: 'GET',
success: function (data) {
self.selectedSection().retValue(data.text); // <-- change here
}
});
And finally, if you're binding to a complex expression in your view you need to invoke it as a function (with no arguments) to get its value:
<span data-bind="text: 'In section: ' + retValue()" />
As a side note, realize that you can leave off the parentheses (consider it syntactic sugar from knockout) if you bind straight to just the observable, e.g.:
<span data-bind="text: retValue" />
Which is effectively equivalent to:
<span data-bind="text: retValue()" />
On a foot note, I see you've used this syntax for a click binding:
...
This works... but only by coincidence. You should realize these things together:
$parent.selectedSection contains the result of ko.observable() which means it is in fact a function that can be invoked
the click data-binding will invoke the expression it gets as a function, passing the contextual data (in your case a Section) to that function
So bascially, when the click happens, this happens:
$parent.selectedSection($data) // where $data == the current Section
Which effectively selects the Section.
It would be more verbose though a lot clearer if the $parent had a function:
var self = this;
self.selectChild = function(section) {
// Possibly handle other things here too, e.g. clean-up of the old selected tab
self.selectedSection(section);
}
And then use the click binding in this clear way:
...
On click the selectChild method will be called, again with the contextual data as the argument.

Answer 2

Instead of this
self.selectedSection().retValue=data.text;
Do this
self.selectedSection(data);