[英]Angular ngIf: Identifier 'length' is not defined
我的組件具有屬性 transfer$ ,它是可觀察到的,可以帶有包含錯誤消息的數組或 object 。 當transfers$為Transfer[]時,我只能輸入[items]。 但即使使用條件
<app-checklist *ngIf="transfers?.length > 0" [items]="transfers"></app-checklist>
angular 繼續警告:
未定義標識符“長度”。 '轉移[] | AppResponseError' 不包含這樣的成員
這是為什么?
謝謝
組件.html
<ng-template #loadingTpl>loading</ng-template>
<ng-template #emptyList let-length="length">
<p *ngIf="length === 0">Empty List</p>
</ng-template>
<ng-template #error let-title="title" let-message="message" let-code="code">
<div *ngIf="code">
Error: {{code}} , {{title}} , {{message}}
</div>
</ng-template>
<div *ngIf="transfers$ | async; let transfers; else loadingTpl">
<app-checklist *ngIf="transfers?.length > 0" [items]="transfers">
<div *ngFor="let transfer of transfers">
..something here
</div>
</app-checklist>
<ng-container *ngTemplateOutlet="emptyList; context: {length: transfers.length}"></ng-container>
<ng-container *ngTemplateOutlet="error; context:transfers"></ng-container>
</div>
TransferService.ts:
import { Injectable } from '@angular/core';
import { of } from 'rxjs';
@Injectable()
export class TransfersService {
transfers$ = of('real observable');
}
組件.ts
import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs';
import { TransfersService } from './TransfersService';
export interface AppResponseError = {code:number,title:string,message:string};
export interface Transfer = {id:number,title:string};
@Component({
selector: 'app-transfer',
})
export class TransferComponent implements OnInit {
transfers$: Observable<Transfer[] | AppResponseError>;
constructor(private transfersService: TransfersService) {
this.transfers$ = this.transfersService.transfers$;
}
ngOnInit() {
this.transfers$.subscribe((data) => {
console.log(data);
});
}
}
您不需要額外的 *ngIf。
<div *ngIf="transfers$ | async; let transfers; else loadingTpl">
這將做的是等到轉帳$ | async 已評估,並將結果綁定到 transfer 的值(非美元后綴)。
在 ts 文件中創建下面的 function。
isDataAvailable(arr){
return Array.isArray(arr) && arr.length >0
}
並像這樣在模板中使用它
<app-checklist *ngIf="isDataAvailable(transfers)" [items]="transfers"></app-checklist>
<div *ngIf="transfers$ | async; let transfers; else loadingTpl">
<app-checklist *ngIf="isDataAvailable(transfers)" [items]="transfers"></app-checklist>
<div *ngFor="let transfer of transfers">
..something here
</div>
<ng-container *ngTemplateOutlet="emptyList; context: {length: transfers.length}"></ng-container>
<ng-container *ngTemplateOutlet="error; context:transfers"></ng-container>
</div>
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