angular 11 的 ngif 子句中的对象可能是 'undefined'
Object is possibly 'undefined' in ngif clause of angular 11
我有一个名为“logManagerService”的服务
import { Injectable } from '@angular/core';
@Injectable({
// this line code make this service as singleton.
providedIn: 'root'
})
export class logManagerService {
private ErrorMessages:string[];
constructor() {
this.ErrorMessages=[];
}
public getErrorMassages():string[]{
return this.ErrorMessages;
}
}
在“display-log.component.html”组件中,我想显示“ErrorMessages”数组的内容。尽管我使用问号来检查 ngif 子句中的未定义,但我收到错误消息“对象可能是 'undefined' “
<div *ngIf="**logManagerService?.getErrorMassages()?.length>0** " class="alert alert-danger">
**<!--Object is possibly 'undefined' -->**
<h5>
Errors
</h5>
<ul>
<li *ngFor="let M of logManagerService.getErrorMassages()">
{{M}}
</li>
</ul>
</div>
我该如何解决?
你可以试试这个:
$any(logManagerService?.getErrorMassages())?.length > 0
我有一个名为“logManagerService”的服务
import { Injectable } from '@angular/core';
@Injectable({
// this line code make this service as singleton.
providedIn: 'root'
})
export class logManagerService {
private ErrorMessages:string[];
constructor() {
this.ErrorMessages=[];
}
public getErrorMassages():string[]{
return this.ErrorMessages;
}
}
在“display-log.component.html”组件中,我想显示“ErrorMessages”数组的内容。尽管我使用问号来检查 ngif 子句中的未定义,但我收到错误消息“对象可能是 'undefined' “
<div *ngIf="**logManagerService?.getErrorMassages()?.length>0** " class="alert alert-danger">
**<!--Object is possibly 'undefined' -->**
<h5>
Errors
</h5>
<ul>
<li *ngFor="let M of logManagerService.getErrorMassages()">
{{M}}
</li>
</ul>
</div>
我该如何解决?
你可以试试这个:
$any(logManagerService?.getErrorMassages())?.length > 0