I have an observable of string Arrays const obs$: Observable<string[]>
on my component as a property. While I can successfully use the async
pipe on a *ngIf
statement, the pipe fails when accessed via array indexer (obs$ | async)[0]
.
Example:
<!-- evaluates the array emmitted by obs$ for truthyness -->
<div *ngIf="obs$ | async">
<!-- only shown if obs$ emitted an array with length > 0 -->
<!-- but this fails with error: Cannot read property '0' of null -->
<img [src]="(obs$ | async)[0]">
</div>
The instance of obs$ is set in the component's constructor, so obs$ shouldn't be undefined when the template is data-bound.
How to properly access the array's elements in the template?
这可能有效
<img [src]="(obs$ | async) ? (obs$ | async)[0] : null">
我会在此级别尝试Elvis运算符,因为开始时您的数据是不确定的:
<img [src]="(obs$ | async)?[0]">
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