blocks|key|1163901|text|您也许可以检查一下可观察到的变化。然后再执行这个动作。就像这样：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1163902|(function+()+{
++++var+cache;
++++ko.bindingHandlers.initValueField+=+{
++++++++init:function+(element,+valueAccessor,+allBindingsAccessor,+viewModel)+{
++++++++++++var+currentValue+=+valueAccessor();
++++++++++++cache+=+currentValue();
++++++++},
++++++++update:function+(element,+valueAccessor,+allBindingsAccessor,+viewModel)+{
++++++++++++var+currentValue+=+valueAccessor();
++++++++++++if+(cache+!==+currentValue())+{
++++++++++++++++alert('Hello+World');
++++++++++++++++cache+=+currentValue();
++++++++++++}
++++++++}
++++};
}());|code-block|syntax|javascript|1163903|缓存变量存储可观察到的旧值。只有当当前值与此旧值不同时，才会执行警报。|offset|length|style|BOLD|1163904|工作小提琴：http://jsfiddle.net/DMLzd/6/|1163905|entityMap|0|LINK|mutability|MUTABLE|url|http://jsfiddle.net/DMLzd/6/^0|0|0|0|2|W|2|0|6|S|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@$I|Z|J|10|K|L]|$I|11|J|12|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@]|9|@$I|14|J|15|1|16]]|A|$]]|$1|O|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

you can perhaps check for changes of the observable. And only then execute the action. Something like this:

<pre><code>(function () {
 var cache;
 ko.bindingHandlers.initValueField = {
 init:function (element, valueAccessor, allBindingsAccessor, viewModel) {
 var currentValue = valueAccessor();
 cache = currentValue();
 },
 update:function (element, valueAccessor, allBindingsAccessor, viewModel) {
 var currentValue = valueAccessor();
 if (cache !== currentValue()) {
 alert('Hello World');
 cache = currentValue();
 }
 }
 };
}());
</code></pre>

The cache variable stores the old value of the observable. The alert is only done when the current value is different from this old one.

the working fiddle: <a href="http://jsfiddle.net/DMLzd/6/" rel="nofollow">http://jsfiddle.net/DMLzd/6/</a>

blocks|key|1166522|text|您可以在自定义绑定中使用element参数来查看调用该绑定的DOM元素。请参阅http://jsfiddle.net/DMLzd/7/中的条件绑定，它使用textbox的id属性来决定是否执行操作。我添加了具有不同ID的附加textbox和按钮，这些ID调用自定义绑定。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1166523|entityMap|0|LINK|mutability|MUTABLE|url|http://jsfiddle.net/DMLzd/7/^0|C|7|2D|2|13|S|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

You can use <code>element</code> argument in your custom binding to see the DOM element that invokes that binding. See <a href="http://jsfiddle.net/DMLzd/7/" rel="nofollow">http://jsfiddle.net/DMLzd/7/</a> for conditional within your custom binding which uses <code>id</code> attribute of textbox to decide whether to perform actions or not. I added additional textbox and button with different ID that invokes the custom binding.

blocks|key|1163928|text|我在这里找到了解决这个问题的潜在方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1163929|Knockout.js性能Gotcha+#3+-所有绑定一起启动|offset|length|1163930|备选方案如下：|1163931|将绑定拆分到单独的元素(可能是容器元素)上。|ordered-list-item|1163932|类似于第1点，但是使用无容器绑定将它们分开。|1163933|使用自定义绑定init中可观察到的计算值手动管理更新。|style|CODE|1163934|entityMap|0|LINK|mutability|MUTABLE|url|http://www.knockmeout.net/2012/06/knockoutjs-performance-gotcha-3-all-bindings.html^0|0|0|W|0|0|0|0|0|7|4|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@$D|10|E|11|1|12]]|A|$]]|$1|F|3|G|5|6|7|13|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|14|8|@]|9|@]|A|$]]|$1|K|3|L|5|J|7|15|8|@]|9|@]|A|$]]|$1|M|3|N|5|J|7|16|8|@$D|17|E|18|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

I found potential workarounds to the problem here:

<a href="http://www.knockmeout.net/2012/06/knockoutjs-performance-gotcha-3-all-bindings.html" rel="nofollow">Knockout.js Performance Gotcha #3 - All Bindings Fire Together</a>

The options are:

<ol>
<li>Split the bindings up by putting them onto separate elements (maybe a container element).</li>
<li>Similar to point 1, but use containerless bindings to separate them out.</li>
<li>Use a computed observable in the custom binding <code>init</code> to manage the updates manually. </li>
</ol>

I have a custom binding that is used to re-initialise a dom element whenever a field ("Type") is changed on the viewmodel. This is defined in an update callback.

<pre><code>&lt;input type="text" data-bind="value: Value, initValueField: Type()" /&gt;

ko.bindingHandlers.initValueField = {
 update:function (element, valueAccessor, allBindingsAccessor, viewModel) {
 alert('Hello World');
 }
};
</code></pre>

See this <a href="http://jsfiddle.net/poztin/DMLzd/3/" rel="nofollow">jsFiddle</a> for a stripped down demo.

As I understand it, one of the conditions for the update being invoked is the following:

<a href="http://www.knockmeout.net/2011/07/another-look-at-custom-bindings-for.html" rel="nofollow">The mechanics of custom bindings</a>

<blockquote>
 Any time that another binding in the same data-bind attribute is
 triggered. This helps ensure things like the value is appropriate when
 the options are changed.
</blockquote>

The issue I have is that this update callback is also called whenever the value on the viewmodel changes.

So...is it possible to either:

<ol>
<li>Suppress one of the bindings from invoking the custom binding.</li>
<li>Detect the source of the invocation inside the custom binding.</li>
</ol>

Conditional update in custom binding

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个自定义绑定，用于每当在视图模型上更改字段("Type")时重新初始化dom元素。这是在更新回调中定义的。<input type="text" data-bind="value: Value, initValueField: Type()" />ko.bindingHandlers.initValueField ...

问自定义绑定中的条件更新
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