ko.dependentObservable 这个方法如何巧妙地理解依赖关系？
我正在用knockoutjs 玩他们的示例，我已经编辑了原始代码，如下所示。 fullName 属性分配为 dependentObservable，并且此方法肯定知道 fullName 方法内的依赖项，因此 fullName 方法仅在依赖项发生更改时才有效。
如果我从 fullName 方法中删除 this.LastName() ，那么更改 lastName 属性不会导致调用 fullName 方法。
我想知道这是怎么发生的。
var viewModel = {
firstName: ko.observable("Bert"),
lastName: ko.observable("Bertington")
};
viewModel.fullName = ko.dependentObservable(function() {
alert('worked');
return this.firstName() + " "+ this.lastName() ;
}, viewModel);
// Activates knockout.js
ko.applyBindings(viewModel);
I am playing with knockoutjs with their samples and i have been edited orginal code bit of which is at below. fullName property assigned as dependentObservable and this method definitely knows which dependencies inside fullName method so fullName method works only if dependencies changed.
If i remove this.LastName() from fullName method so changing lastName property does not cause invoke fullName method.
I wonder how this is happening.
var viewModel = {
firstName: ko.observable("Bert"),
lastName: ko.observable("Bertington")
};
viewModel.fullName = ko.dependentObservable(function() {
alert('worked');
return this.firstName() + " "+ this.lastName() ;
}, viewModel);
// Activates knockout.js
ko.applyBindings(viewModel);
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Knockout 中有一个依赖跟踪机制，在评估 dependentObservables 时使用。关键是访问可观察对象必须通过一个函数（您必须调用
this.firstName()）。除了返回firstName之外，Knockout还将dependentObservable添加为firstName的订阅者。当firstName更新时（再次必须通过该函数），所有订阅者都会收到通知。此外，每次评估 dependentObservable 时，都会重新评估这些依赖关系，因此，dependentObservable 的依赖关系实际上可能会随着时间的推移而发生变化。
There is a dependency tracking mechanism in Knockout that is used while evaluating dependentObservables. The key is that accessing an observable has to go through a function ( you have to call
this.firstName()). Along with returning the firstName, Knockout adds the dependentObservable as a subscriber tofirstName. WhenfirstNameis updated (which again has to go through the function), then all subscribers are notified.Also, these dependencies are re-evaluated each time that a dependentObservable is evaluated, so the dependencies can actually change over time for a dependentObservable.