将 ko.computeds（Knockout 计算）应用于 Durandal 视图模型的正确方法是什么？

Question

我是 Durandal 的新手，在视图模型中应用 ko.computed 方法时运气不佳。谁能告诉我正确的语法或模式是什么？

您可以在https://github.com/robksawyer/durandal-todo/blob/master/views/todos.html查看整个项目。

我应用的每个计算在绑定期间都会出现以下错误。

Error("Cannot write a value to a ko.computed unless you specify a 'write' option. If you wish to read the current value, don't pass any parameters.")

compose 方法请求视图模型和视图：

<!--ko compose: { 
        model: router.activeItem, //wiring the router
        afterCompose: router.afterCompose, //wiring the router
        cacheViews: false, //telling composition to keep views in the dom, and reuse them (only a good idea with singleton view models)
        transition: 'fadein'
    }--><!--/ko-->

视图模型：

// count of all completed todos
    var completedCount = ko.computed(function () {
        return ko.utils.arrayFilter(todos(), function (todo) {
            return todo.completed();
        }).length;
    });

查看 https://github.com/robksawyer/durandal-todo/blob/master/views/todos.html

错误截图

Answer 1

首先定义 vm 单例，然后添加 ko.computed 方法很可能会处理该错误消息。

var vm = {
   current : current,
   todos: todos,
   ... // remove ko.computeds from the singleton
};

vm.completedCount = ko.computed(function () {
    return ko.utils.arrayFilter(todos(), function (todo) {
        return todo.completed();
    }).length;
}, vm);

// add other ko.computeds

return vm;

Answer 2

我的问题似乎是对控制台消息和 Knockout 工作原理的误解。你可以在Durandal TodoMVC - Cannot write a value to a ko.computed看到解释。​​