强制运行计算属性函数 [英] Force a computed property function to run

问题描述

给出计算属性

vm.checkedValueCount = ko.computed(function(){
  var observables = getCurrentValues();  //an array of ko.observable[]
  return _.filter(observables, function(v) { return v() }).length;
});

假设getCurrentValues()可以返回不同的可观察对象集，这些可观察对象集在代码的其他地方进行了修改(并且来自比observableArray更复杂的结构).

suppose getCurrentValues() can return different sets of observables which are modified elsewhere in the code (and comes from a more complex structure than an observableArray).

我需要checkedValueCount随时进行更新

• 其依赖项之一更改
• getCurrentValues()返回一组不同的可观察值.

问题在于，ko.computed似乎记住了最后一个返回的值，并且仅在依赖项更新时才更新.这可以处理第一种情况，但不能处理后者.

The problem is that ko.computed seems to memoize the last returned value and only update when a dependency updates. This handles the first case but not the latter.

我正在寻找的是一种强制重新运行checkedValueCount的方法.我可以使用的东西是这样的:

What I'm looking for is a way to force checkedValueCount to re-run. Something which I can use like:

changeCurrentValues();
vm.checkeValueCount.recalculate();

考虑到我拥有的话，最简单地输入

Put most simply, given that I have

a = ko.computed(function() { return Math.random() })

如何强制两次调用a()以返回不同的值.

how can I force invoking a() twice to return different values.

推荐答案

我意识到我的第一个答案错过了您的观点，并且无法解决您的问题.

I realized my first answer missed your point, and won't solve your issue.

问题在于，只有在存在一些可观察到的强迫其重新评估的情况下，计算者才会重新评估.没有原生方法可以强制计算结果重新评估.

The problem is that a computed will only reevaluate if there is some observable that forces it to re-evaluate. There is no native way to force a computed to re-evaluate.

但是，您可以通过创建一个虚拟的可观察值，然后告知其订户它已更改，来解决一些黑客问题.

However, you can get around this with some hackery by creating a dummy observable value and then telling its subscribers that it has changed.

(function() {

    var vm = function() {
        var $this = this;

        $this.dummy = ko.observable();

        $this.curDate = ko.computed(function() {
            $this.dummy();
            return new Date();
        });

        $this.recalcCurDate = function() {
            $this.dummy.notifySubscribers();
        };        
    };

    ko.applyBindings(new vm());

}());​

这是一个小提琴，显示了这种方法

这篇关于强制运行计算属性函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！