Angular Ivy strictTemplates true 类型 'boolean |null' 不可分配给类型 'boolean' [英] Angular Ivy strictTemplates true Type 'boolean | null' is not assignable to type 'boolean'

问题描述

我已将我的应用更新到 9 版本.一切都很好，但我有问题将strictTemplates 设置为true.例如这段代码

I've updated my app to 9 version. Everything is alright but I've problem with strictTemplates set to true. For instance this code

loaded$: Observable<boolean>
[loaded]="loaded$ | async"
@Input() loaded!: boolean;

我收到错误类型 'boolean |null' 不能分配给类型 'boolean'.

I've got the error Type 'boolean | null' is not assignable to type 'boolean'.

修复错误

@Input() loaded!: boolean | null;

但是我看不到有人acn解释我的意思，好吗?

But I cant see the point someone acn explain me, please?

推荐答案

原因是因为 async 管道返回签名类似于 (input$: Observable;): T |null 总是，因为它在等待来自异步调用的响应时向模板返回 null.

The reason is because the async pipes return signature is something like <T>(input$: Observable<T>): T | null always, because it returns null to the template while it's awaiting a response from an asynchronous call.

更多相关信息:https://angular.io/guide/模板类型检查#strict-null-checks

你可以做你做过的事情并允许空值，或者如果你知道它永远不会为空，使用非空断言运算符:

You can do what you've done and allow null, or if you know it will never be null, use a non null assertion operator:

[loaded]="(loaded$ | async)!"

或在此处禁用类型检查:

or disable type checking here:

[loaded]="$any(loaded$ | async)"

或者对于这种特殊情况，您可能可以这样做:

or for this particular case you could probably do something like this:

[loaded]="(loaded$ | async) || false"

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