使用ko.utils.arrayForEach迭代observableArray

Question

我试图计算'observableArray'的'price'字段的总和.到目前为止,我有以下代码:

(function(){

function objFeatures(name,price) {
        return {
            name: ko.observable(name),
            price: ko.observable(price),

            removeFeatures: function () {
                appViewModel.features.remove(this);
            }
        }
    }

var appViewModel = {
features: ko.observableArray([
            new objFeatures("Feature1", 20),
            new objFeatures("Feature2", 20)
        ]),

 grandTotal: ko.computed(function () {
            var total = 0;
            ko.utils.arrayForEach(this.features(), function () {
                total += this.price();
            })
            return total;
        })
};

ko.applyBindings(appViewModel);

}());

当我尝试运行它时,我在firebug控制台中得到一个"错误:this.features不是函数".

我究竟做错了什么？

Answer 1

在创建期间立即评估计算的可观察量.在您的情况下,appViewModel尚未创建,this不会代表appViewModel.

this在这种情况下,有很多方法可以确保这是正确的.这是两个:

1. 在初始对象文字之外创建它:

   var appViewModel = {
      features: ko.observableArray([
          new objFeatures("Feature1", 20),
          new objFeatures("Feature2", 20)
          ])
   };
   
   appViewModel.grandTotal = ko.computed(function() {
       var total = 0;
       ko.utils.arrayForEach(this.features(), function(feature) {
           total += feature.price();
       });
   
       return total;
   }, appViewModel);
   

2. 在函数中创建视图模型:

   var AppViewModel = function() {
       this.features = ko.observableArray([
           new objFeatures("Feature1", 20),
           new objFeatures("Feature2", 20)
       ]);
   
       this.grandTotal = ko.computed(function() {
           var total = 0;
           ko.utils.arrayForEach(this.features(), function(feature) {
               total += feature.price();
           });
           return total;
       }, this);
   };
   
   ko.applyBindings(new AppViewModel());?