我想知道 ngOnChanges 回调是如何工作的。所以我添加了它来观察使用 Input 装饰器注释的属性的变化，如下所示：
@Input() postsToAddToList: Post[] = [];
现在，当我编译代码时，我添加了一些值，这些值会导致使用@Input 注释的属性发生更改，但这不会导致调用和执行 ngOnChanges 回调。请参阅下面发布的屏幕截图中显示的日志。
我想查看浏览器中显示的 ngOnChanges 中的日志。请让我知道是什么阻止了正确调用和调用 ngOnChanges
app.component.ts：
import { Component } from '@angular/core';
import { Post } from './post-create/post-create.component';
@Component({
selector: 'app-root',
templateUrl: './app.component.html',
styleUrls: ['./app.component.css']
})
export class AppComponent {
title = 'binding2';
postsArray: Post[] = [];
onReceiveSubmittedEvtEmitter(post: Post) {
this.postsArray.push(post);
console.log("onReceiveSubmittedEvtEmitter->: post.title: " + post.title);
console.log("onReceiveSubmittedEvtEmitter->: post.content:" + post.content);
}
}
app.component.html：
<app-post-create (onPostSubmittedEvtEmitter)="onReceiveSubmittedEvtEmitter($event)"></app-post-create>
<app-post-list [postsToAddToList]="postsArray"></app-post-list>
post-list.component.ts：
import { Component, Input,OnInit, OnChanges, SimpleChanges,Output, EventEmitter } from '@angular/core';
import { Post } from '../post-create/post-create.component';
@Component({
selector: 'app-post-list',
templateUrl: './post-list.component.html',
styleUrls: ['./post-list.component.css']
})
export class PostListComponent implements OnInit {
constructor() {}
@Input() postsToAddToList: Post[] = [];
ngOnInit(): void {}
ngOnChanges(changes: SimpleChanges) {
for (let changedProperty in changes) {
if (changes.hasOwnProperty(changedProperty)) {
console.log("ngOnChanges->: changedProperty: " + changedProperty);
console.log("ngOnChanges->: changedProperty:" + changedProperty);
switch(changedProperty) {
case 'postsToAddToList':
console.log("ngOnChanges->: changes[changedProperty].previousValue: " + changes[changedProperty].previousValue);
console.log("ngOnChanges->: changes[changedProperty].currentValue):" + changes[changedProperty].currentValue);
break;
}
}
}
}
}
post-list.component.html：
<!-- post-list.component.html -->
<h3>List</h3>
<ng-container *ngIf="postsToAddToList.length; else elseTemplate">
<ul class="list-group">
<li class="list-group-item" *ngFor="let post of postsToAddToList; let i = index">
<h5>{{i+1}}) {{post.title}}</h5>
<p>
{{post.content}}
</p>
</li>
</ul>
</ng-container>
<ng-template #elseTemplate>
<div class="alert alert-danger" role="alert">
No Post Found!
</div>
</ng-template>
错误截图：
