子组件中的Angular @Input也会更新父组件中的值

Question

在角度中，属性上的@Input与[propertyNameInParent] =“propertyNameInChild”结合使用，允许我们将父属性的值绑定到子属性。也称为单向绑定。扼杀，在我的情况下，它也在更新父类中的属性。这怎么可能？

父组件 - > favorite-cities子组件 - > city-detail

因此，基本上在（点击）事件中，最喜欢的城市是select（selectedCity属性）。然后在城市细节组件中，城市可以通过单击onPlusIconClick（）来接收喜欢。不知怎的，这也引发了最受欢迎城市的城市化进程。为什么我不必使用eventemitter将更新后的值发送回父组件？

最喜欢的，cities.component.ts

import {Component, OnInit} from '@angular/core';
import {CitiesService} from '../../services/cities.service';
import {City} from '../../model/city';

@Component({
selector: 'app-favorite-cities',
templateUrl: './favorite-cities.component.html',
styleUrls: ['./favorite-cities.component.css']
})
export class FavoriteCitiesComponent implements OnInit {

cities: City[];
selectedCity: City;

constructor(private citiesService: CitiesService) {
}

ngOnInit() {
    this.citiesService.getCities().subscribe(
        (data) => this.cities = data,
        (err) => console.log(err),
        () => { }
    );
}

setSelectedCity(city: City): void {
    this.selectedCity = city;
}

}

最喜欢的，cities.component.html

<div class="container-fluid">
    <div class="row justify-content-center">
        <div class="col-4">
            <h2>Mijn favoriete steden zijn: </h2>
            <ul class="list-group" *ngFor="let city of cities">
                <li class="list-group-item" (click)="setSelectedCity(city)">{{city.id}} - {{city.name}}
                    <span class="float-right badge badge-success">Likes {{city.rating}} .   </span>
                </li>
            </ul>
        </div>
        <div class="col-4">
            <app-city-detail [selectedCity]="selectedCity"></app-city-detail>
        </div>
    </div>
</div>

城市detail.component.ts

import {Component, Input, OnInit} from '@angular/core';
import {City} from '../../model/city';
import {CitiesService} from '../../services/cities.service';

@Component({
selector: 'app-city-detail',
templateUrl: './city-detail.component.html',
styleUrls: ['./city-detail.component.css']
})
export class CityDetailComponent implements OnInit {

@Input()
selectedCity: City;

constructor(private citiesService: CitiesService) {
}

ngOnInit() {
}

onMinusIconClick(): void {
    if (this.selectedCity.rating > 0) {
        this.selectedCity.rating -= 1;
    }
    this.citiesService.updateRatingOfCity(this.selectedCity).subscribe(
        (data) => { console.log('oaksdoaks'); },
    );

}

onPlusIconClick(): void {
    this.selectedCity.rating += 1;
    this.citiesService.updateRatingOfCity(this.selectedCity).subscribe();
}
}

城市detail.component.html

<div *ngIf="selectedCity">
<div class="container-fluid">
    <div class="row">
        <h2>City details</h2>
        <div class="col-1">
            <i (click)="onPlusIconClick()" class="fas fa-2x fa-plus-square"></i>
        </div>
        <div class="col-1">
            <i (click)="onMinusIconClick()" class="fas fa-2x fa-minus-square"></i>
        </div>
    </div>
</div>
<ul class="list-group">
    <li class="list-group-item">Naam: {{selectedCity.id}} </li>
    <li class="list-group-item">Provincie: {{selectedCity.provincie}}</li>
    <li class="list-group-item">Highlights: {{selectedCity.highlights}} </li>
</ul>
<img class="img-fluid" src="assets/img/{{selectedCity.name.trim()}}.jpg" >

Answer 1

因为你正在输入一个对象，这只是一个reference。因此父级和子级具有引用完全相同对象的属性。

如果这是不需要的行为，则必须在设置所选城市时创建浅色副本。或者在您更新的任何其他地方..有很多选择：

setSelectedCity(city: City): void {
  this.selectedCity = { ...city }; //shallow copy
}