在ko.observableArray上计算ko。

Question

I'm trying to use a computed to calculate the total of some product.

function productViewModel(){

    self = this;
    function productModel(data)
    {
        var self=this;
        self.id=ko.observable(data.id);
        self.codigo=ko.observable(data.codigo);
        self.recurso=ko.observable(data.recurso);
        self.unidad=ko.observable(data.unidad);
        self.precio_unitario=ko.observable(0);
        self.cantidad=ko.observable(0);
        self.total=ko.computed(function()
            {
                return self.precio_unitario()*self.cantidad(); 
            },productModel); 
    }

    self.products = ko.observableArray([]);

    self.addProduct = function(product)
    {
        self.products.push(new productModel(product));
    };
    self.removeProduct = function()
    {
        self.products.remove(this);
    };

}

orden = new productViewModel()
ko.applyBindings(orden);

But when precio_unitario and cantidad are changed. total doesn't update.

Answer 1

function productModel(data)
{
    var self=this;
    ...
    self.total=ko.computed(function()
        {
            return self.precio_unitario()*self.cantidad(); 
        },this); 
}

You should be binding the ko.computed to this not to the function. You want it to be bound to the object thats created, not to the constructor, which won't have those properties on it. Since you're using self, this will actually be taken care of by default, and if you like you can omit the second argument entirely.

Within the constructor function, this or self will refer to the object that is created when you use the new operator. So all the properties will be created on that object.

Answer 2

self = this; should be var self = this; ; otherwise you're overwriting the global self . Also take out ,productModel on the computed; it's not necessary.

Important parts:

function productViewModel() {
    var self = this;

    function productModel(data) {
        var self = this;
        ...
        self.total = ko.computed(function() {
            return self.precio_unitario()*self.cantidad(); 
        });
    }
    ...
}

Also it's important make sure you're always using the correct format for writing to observables. It should be self.catidad(newValue); and not self.catidad = newValue;