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I'm studying knockoutjs and having some issues. I have ASP.NET MVC page with a method returning list of three Car objects is JSON. I than map it to select in HTML view and I want to display cost of a selected car on selection change. The problem is that a name of a car is visible while a price is not ('A Mercedes-Benz costs .'). What it could be? Thanks in advance!
Controller:
public class Car
{
public string Make { get; set; }
public decimal Price { get; set; }
}
public JsonResult GetCars()
{
List<Car> cars = new List<Car>();
cars.Add(new Car { Make = "Mercedes-Benz", Price = 103000 });
cars.Add(new Car { Make = "Toyota", Price = 37000 });
cars.Add(new Car { Make = "Huyndai", Price = 17000 });
return Json(cars, JsonRequestBehavior.AllowGet);
}
And View with Javascript code:
<head>
<script type="text/javascript" src="~/Scripts/jquery-2.0.3.min.js"></script>
<script type="text/javascript" src="~/Scripts/knockout-3.0.0.js"></script>
<script type="text/javascript">
$(document).ready(function () {
function Car(data) {
this.Make = ko.observable(data.Make);
this.Price = ko.observable(data.Price);
}
function CarsViewModel() {
var self = this;
//Data
self.someOptions = ko.observableArray([]);
self.myOption = ko.observable();
//Operations
self.initData = function () {
$.get('/Home/GetCars', function (data) {
var mappedCars = $.map(data, function (item) { return new Car(item) });
self.someOptions(mappedCars);
});
}
}
ko.applyBindings(new CarsViewModel());
});
</script>
</head>
<body>
<div>
<button data-bind="click: initData">Load data</button>
<h4>Preview</h4>
<p>
<select data-bind="options: someOptions, optionsText: 'Make', value: myOption"></select><br />
A <span data-bind="text: myOption().Make"></span> costs <span data-bind="text: myOption().Price"></span>.
</p>
</div>
</body>
593
If you check your browser's JavaScript console you should see the following error:
Uncaught TypeError: Unable to process binding "text: function (){return myOption().Make }" Message: Cannot read property 'Make' of undefined
You get this error because when your page is loaded your myOption is empty so it does not have a Make and Price properties. So KO cannot execute the binding data-bind="text: myOption().Make" and it stops with the processing of the further bindings.
After calling initData now you have something in myOption but still all the bindings after the data-bind="text: myOption().Make" won't work anymore.
To solve this there are multiple ways like:
data-bind="text: myOption() && myOption().Make"
with binding
Here is an example for the with binding:
<!-- ko with: myOption -->
A <span data-bind="text: Make"></span>
costs <span data-bind="text: Price"></span>.
<!-- /ko -->
Demo JSFiddle.
178
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