Angular组件间怎么进行交互?常用交互方法介绍
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1、通过输入型绑定把数据从父组件传到子组件
child.component.ts
export class ChildComponent implements OnInit { @Input() hero: any; @Input('master') masterName: string; // 第二个 @Input 为子组件的属性名 masterName 指定一个别名 master constructor() { } ngOnInit(): void { } }
child.component.html
<div style="background-color: #749f84"> <p>child works!</p> <h3>{{hero?.name}} says:</h3> <p>I, {{hero?.name}}, am at your service, {{masterName}}.</p> </div>
parent.component.ts
export class ParentComponent implements OnInit { hero = {name: 'qxj'} master = 'Master' constructor() { } ngOnInit(): void { } }
parent.component.html
<app-child [hero]="hero" [master]="master"></app-child>
2、父组件监听子组件的事件
child.component.ts
export class ChildComponent implements OnInit { @Input() name: string; @Output() voted = new EventEmitter<boolean>(); didVote = false; vote(agreed: boolean) { this.voted.emit(agreed); this.didVote = true; } constructor() { } ngOnInit(): void { } }
child.component.html
<h4>{{name}}</h4> <button (click)="vote(true)" [disabled]="didVote">Agree</button> <button (click)="vote(false)" [disabled]="didVote">Disagree</button>
parent.component.ts
export class ParentComponent implements OnInit { agreed = 0 disagreed = 0 voters = ['Narco', 'Celeritas', 'Bombasto'] onVoted(agreed: boolean) { agreed ? this.agreed++ : this.disagreed++ } constructor() { } ngOnInit(): void { } }
parent.component.html
<h2>Should mankind colonize the Universe?</h2> <h3>Agree: {{agreed}}, Disagree: {{disagreed}}</h3> <app-child *ngFor="let voter of voters" [name]="voter" (voted)="onVoted($event)"></app-child>
3、父组件与子组件通过本地变量互动
父组件不能使用数据绑定来读取子组件的属性或调用子组件的方法。但可以在父组件模板里,新建一个本地变量来代表子组件,然后利用这个变量来读取子组件的属性和调用子组件的方法,如下例所示。
子组件 CountdownTimerComponent
进行倒计时,归零时发射一个导弹。start
和 stop
方法负责控制时钟并在模板里显示倒计时的状态信息。
child.component.ts
export class ChildComponent implements OnInit, OnDestroy { intervalId = 0 message = '' seconds = 11 clearTimer() { clearInterval(this.intervalId) } ngOnInit() { this.start() } ngOnDestroy() { this.clearTimer() } start() { this.countDown() } stop() { this.clearTimer() this.message = `Holding at T-${this.seconds} seconds` } private countDown() { this.clearTimer() this.intervalId = window.setInterval(() => { this.seconds -= 1 if (this.seconds === 0) { this.message = 'Blast off!' } else { if (this.seconds < 0) { this.seconds = 10 } // reset this.message = `T-${this.seconds} seconds and counting` } }, 1000) } }
child.component.html
<p>{{message}}</p>
parent.component.ts
export class ParentComponent implements OnInit { constructor() { } ngOnInit(): void { } }
parent.component.html
<h3>Countdown to Liftoff (via local variable)</h3> <button (click)="child.start()">Start</button> <button (click)="child.stop()">Stop</button> <div class="seconds">{{child.seconds}}</div> <app-child #child></app-child>
4、父组件调用@ViewChild()
这个本地变量方法是个简单便利的方法。但是它也有局限性,因为父组件-子组件的连接必须全部在父组件的模板中进行。父组件本身的代码对子组件没有访问权。
如果父组件的类需要读取子组件的属性值或调用子组件的方法,就不能使用本地变量方法。
当父组件类需要这种访问时,可以把子组件作为 ViewChild,***注入***到父组件里面。
countdown-parent.component.ts
import {AfterViewInit, Component, ViewChild} from '@angular/core' import {ChildComponent} from '../child/child.component' @Component({ selector: 'app-parent-vc', template: ` <h3>Countdown to Liftoff (via ViewChild)</h3> <button (click)="start()">Start</button> <button (click)="stop()">Stop</button> <div class="seconds">{{ seconds() }}</div> <app-child></app-child> `, }) export class CountdownParentComponent implements AfterViewInit { @ViewChild(ChildComponent) private timerComponent: ChildComponent seconds() { return 0 } ngAfterViewInit() { // Redefine `seconds()` to get from the `ChildComponent.seconds` ... // but wait a tick first to avoid one-time devMode // unidirectional-data-flow-violation error setTimeout(() => { this.seconds = () => this.timerComponent.seconds }, 0) } start() { this.timerComponent.start() } stop() { this.timerComponent.stop() } }
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