如何扩展淘汰赛 observables 以从绑定中读取默认值? [英] How to extend knockout observables to read default value from binding?

问题描述

我终于有时间开始学习 KnockoutJS，同时构建一个新的 MVC4 应用程序.我试图找出从视图中已设置的默认值初始化可观察值的最佳方法.

I have finally found the time to start learning KnockoutJS while building a new MVC4 application. I am trying to figure out the best way to initialize an observable value from a default value that is already set in the view.

这是一个人为的例子，但我想将可观察对象的默认值直接渲染到视图中，如下所示:

This is a contrived example, but I would like to render out a default value for an observable directly to the view as follows:

<input type="hidden" 
       value="@Model.SomeValue"
       data-bind="value: myObservableReference"/>

我知道默认值通常通过以下方式初始化:

I know that a default value is normally initialized via:

model.myObservableReference = ko.obervable("SomeValue");

但是，我想找到一种扩展初始化的方法:

However, I would like to find a way to extend the initialization such that:

model.myObservableReference = ko.obervable();

如果值存在，将从绑定中读取现有值.

would read the existing value from the binding if a value exists.

由于到目前为止我已经设法让我的 KnockoutJS 代码完全不知道剃刀世界，我想避免草率:

As I have so far managed to keep my KnockoutJS code completely unaware of the razor world, I want to to avoid the sloppiness of:

model.myObservableReference = ko.obervable(@Model.SomeValue);

我猜这将通过扩展程序或自定义绑定器来处理，但如果有人能指出我正确的方向，我将不胜感激.

I am guessing this would be handled via either an extender or custom binder, but if someone could point me in the right direction it would be greatly appreciated.

推荐答案

您可以尝试创建自己的自定义绑定处理程序来实现此目的:

You could try creating your own custom binding handler to achieve this:

ko.bindingHandlers.initializeValue = {
    init: function(element, valueAccessor) {
        valueAccessor()(element.getAttribute('value'));
    },
    update: function(element, valueAccessor) {
        var value = valueAccessor();
        element.setAttribute('value', ko.utils.unwrapObservable(value))
    }
};

<input type="hidden" value="@Model.SomeValue"
       data-bind="initializeValue:myObservableReference, value: myObservableReference"/>

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