为什么 observable 不通知 if block in knockout？

Question

如果在选择更改时未通知绑定，则敲除。选择更改时，如果所选国家/地区 'eu' 设置为“1”，我希望发生一些事情。

<select data-bind="options: countries,
    optionsText: function(item) {
    return item.country_name
    },
    value:selectedCountry">
</select>

<!-- These *ARE* all updated when country selection changes -->
<div data-bind="visible: selectedCountry()">
    <span data-bind="text: selectedCountry().eu"></span>
    <span data-bind="text: selectedCountry().country_name"></span>
    <span data-bind="text: selectedCountry().country_code"></span>
</div>

<!-- This is *NOT* updated -->
<!-- ko if: selectedCountry().eu === "1" -->
    <span>You selected country from EU
    </span>
<!-- /ko -->

'countries'（示例）如下。

{
    "countries": [
        {
            "country_code": "BD",
            "country_name": "Bangladesh",
            "eu": "0"
        },
        {
            "country_code": "BE",
            "country_name": "Belgium",
            "eu": "1"
        }
     ]
 }

更新

我正在使用 CoffeeScript

@selectedCountry = ko.observable()
@countries = ko.observableArray []

Answer 1

它对我有用fiddle。不确定我的代码和你的有什么区别，因为我们看不到你 JavaScript.

https://jsfiddle.net/xggu9Lv2/7/

var countries =  [
        {
            "country_code": "A2",
            "country_name": "Satellite Provider",
            "eu": "0"
        },
        {
            "country_code": "A2",
            "country_name": "Satellite Provider",
            "eu": "1"
        }
     ]

var ViewModel = function() {
    var self = this;
    self.countries = ko.observableArray(countries);
    self.selectedCountry = ko.observable(null);
};

ko.applyBindings(new ViewModel()); 

<select data-bind="options: countries,
    optionsText: function(item) {
    return item.country_name
    },
    value:selectedCountry">
</select>

<div data-bind="visible: selectedCountry()">
    <span data-bind="text: selectedCountry().eu"></span>
    <span data-bind="text: selectedCountry().country_name"></span>
    <span data-bind="text: selectedCountry().country_code"></span>
</div>

<!-- ko if: selectedCountry().eu === "1" -->
    <span>You selected country from EU
    </span>
<!-- /ko -->

为什么 observable 不通知 if block in knockout？

why is observable not notifying if block in knockout?

coffeescript

knockout.js