在我的角度应用程序中,我定义了模型类:
import {Type} from "class-transformer"; //https://github.com/typestack/class-transformer
export class Case {
id: string;
@Type(() => Date)
created: string;
status: string;
get customMethod() {
return `Hello ${this.id}`;
}
isPending() {
console.log('isPending() called...');
return this.status == 'new';
}
}
在我的组件中,我从rest api获取案例:
ngOnInit() {
this.api.getCases().subscribe((cases) => {
this.cases = cases;
});
}
和getCases()看起来像:
import {plainToClass} from "class-transformer";
import {Case} from "../models/Case";
// ... come other code
public getCases() {
return this.http.get(`${this.apiUrl}/cases`).pipe(map(response => {
return plainToClass(Case, response as Case[])
}))
}
工作正常,在我的组件中,我获得了Case实例。我将这些实例传递给其他子组件:
<app-case-listing [case]="case" *ngFor="let case of cases"></app-case-listing>
那个子组件模板就是:
<li [class.pending]="case.isPending()">
li element for case {{case.customMethod}}, {{case.status}}
</li>
所有方法都可以正常工作-除了isPending()似乎是在循环中调用之外。我不确定这是否是预期的行为(或者在性能方面是否良好)。当我将控制台日志添加到“ customMethod” getter时,其日志也会循环登录。
控制台输出看起来像(成千上万条这样的消息):
isPending() called...
6
breadcrumbs.js:58 isPending() called...
zone.js:2279 [Violation] 'setTimeout' handler took 168ms
6
breadcrumbs.js:58 isPending() called...
6
breadcrumbs.js:58 isPending() called...
zone.js:2279 [Violation] 'setTimeout' handler took 185ms
6
breadcrumbs.js:58 isPending() called...
6
breadcrumbs.js:58 isPending() called...
zone.js:2279 [Violation] 'setTimeout' handler took 186ms
6
breadcrumbs.js:58 isPending() called...
6
breadcrumbs.js:58 isPending() called...
6
breadcrumbs.js:58 isPending() called...
6
breadcrumbs.js:58 isPending() called...
zone.js:2279 [Violation] 'setTimeout' handler took 197ms
所以,我的问题是:
答案 0 :(得分:1)
这是正确的行为,您在isPending
循环内调用ngFor
方法,并且该方法为每个Case
实例调用。您可以将ChangeDetectionStrategy.OnPush添加到app-case-listing
组件中,以避免不必要的检查。