获得一次性绑定以用于ng-if [英] Get one-time binding to work for ng-if

问题描述

这个问题已经问过，但是我可以.不能使该解决方案有效，所以我想知道我的具体信息是否有所不同.

This question has been asked before, but I can't get that solution working, so I'm wondering if there's something different in my specifics.

代码非常非常简单:

<h1 ng-if="vm.building.name !== undefined">update {{vm.building.name}}</h1>

如所写，此代码片段工作正常.如果设置了 vm.building.name ，则会显示标记.

As written, this snippet works fine. If vm.building.name is set, tag appears.

但是，如果我尝试进行一次性绑定，那就是:

However, if I try to make the one-time binding work, that is:

<h1 ng-if="::vm.building.name !== undefined">update {{vm.building.name}}</h1>

标签根本没有出现.我尝试过变体:

The tag doesn't appear at all. I've tried variations:

<h1 ng-if="::(vm.building.name !== undefined)">update {{vm.building.name}}</h1>

仍然没有.这是一件令人沮丧的简单事情.糟糕，该代码似乎可以在 jsfiddle 中使用，但我无法使其在我的特定应用程序中正常工作.某处有设置吗?我需要更改一些琐事吗?

Still nope. It's such a frustratingly simple thing. Hell, the code seems to work in a jsfiddle, but I can't get it working for my particular app. Is there a setting somewhere? Some random bit of trivia I need to change?

如果有的话，我在这里使用角度 1.5.7 .

Is there I'm using angular 1.5.7, if that matters.

<h1 ng-if="vm.building.name !== undefined">update {{::vm.building.name}}</h1>

也就是说，设置 {{:: vm.building.name}} 最终会给我我想要的结果，但要付出额外的无用观察者的代价，对吗?

That is, setting the {{::vm.building.name}} ultimately gives me the result I'm looking for, but at the cost of a additional, useless watcher, right?

进一步编辑内容:出于多种原因，这不是一个很好的解决方案.

Further edit on my edit: this isn't a great solution for a number of reasons.

我的问题源于一个事实，即 vm.building.name 等待API调用，因此错过了第一个 $ watch 摘要(我认为).因此，有一种方法可以使 ng-if 在第一次设置 vm.building.name 之后直接执行它的工作，而不是用angular定义的一次性"时间然后退出吗?

My problem stems from the fact that vm.building.name waits on an API call and therefore misses the first $watch digest (I think). So instead of "one-time" as defined by angular, is there a way to have ng-if do its thing directly after vm.building.name is set the first time and then quit?

推荐答案

好，在这里，您要使用 undefined 检查一次性数据绑定 vm.building.name 值，并且由于它是一次性数据绑定，因此此条件将始终为false.

Well, In here you're checking one-time data binding vm.building.name value with undefined and since it is one-time data binding this condition will always be false.

修改您的 ng-if 并使它更简单

<h1 ng-if="::vm.building.name">update {{::vm.building.name}}</h1>

请找到工作的监听器: https://plnkr.co/edit/QA6ZA7e0zHnN45oQWzQH?p=preview

Please find working plunker : https://plnkr.co/edit/QA6ZA7e0zHnN45oQWzQH?p=preview

这可以工作！

干杯！

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