"v.context.$ implicit.categories [0]未定义". Ionic 3中的错误 [英] "v.context.$implicit.categories[0] is undefined" error in Ionic 3

问题描述

我正在尝试使用WordPress rest API访问离子产品的类别标签.在<h3 class="product-name uppercase">{{productdetail?.categories[0].slug}}</h3>上这似乎在一页上可以正常工作，但是当我尝试在另一页上的Angle中实现相同的for循环时，这似乎不起作用

I am trying to access the category slug for a product in ionic using the WordPress rest API. This seems to work fine on one page as <h3 class="product-name uppercase">{{productdetail?.categories[0].slug}}</h3> however this does not seems to work when i try implementing the same using for loop in angular on another page

<div class="width50" *ngFor="let object of dataList">
    <img src="{{object.images[0].src}}" width="150"  (click)="navigateToPage(object.id)" />
    <h3 class="product-name uppercase" text-nowrap>{{object?.categories[0].slug}}</h3> 
</div>

出现错误，显示为v.context.$implicit.categories[0] is undefined，但是在同一页面上，图像源代码似乎可以正常工作.

it gives an error as v.context.$implicit.categories[0] is undefined however on same page the code for image source seems to work fine.

推荐答案

根据

Angular安全导航操作符(?.)流畅且方便 防止属性路径中的空值和未定义值的方法.这里 是的，如果currentHero为 空.

The Angular safe navigation operator (?.) is a fluent and convenient way to guard against null and undefined values in property paths. Here it is, protecting against a view render failure if the currentHero is null.

这样写就可以

obj?.foo

angular会将其转换为以下表达式.

angular will transform it to the following expression.

obj == null ? null : obj.foo

因此，如果obj为空值，则不会看到任何错误.

so if the obj is empty value then you won't see any of errors.

您可以使用表达式

object?.categories[0]?.slug

将被转换为

object == null ? null : object.categories[0] == null ? null : object.categories[0].slug;

如果您不知道对象是否包含任何值，或者异步加载数据并且对象第一次为undefined，则安全导航运算符会很有帮助.

Safe navigation operator is helpful if you don't know whether your object contains any value or not, or you load data asynchronously and your object is undefined at first time.

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