父傳子用@input

子傳父用@output

例：子組件

<p>
    <span *ngFor="let star of stars;let i=index" class="glyphicon glyphicon-star" [class.glyphicon-star-empty]="star" (click)="clickStar(i)"></span>
    <span>{{rating | number:‘1.0-2‘}}星</span>  //保留兩位小數
</p>

import { Component, OnInit ,Input ,Output,EventEmitter,OnChanges,SimpleChanges } from ‘@angular/core‘;

@Component({
  selector: 
 
‘app-stars‘,
  templateUrl: ‘./stars.component.html‘,
  styleUrls: [‘./stars.component.scss‘]
})
export class StarsComponent implements OnInit, OnChanges {

  //發生改變時，初始化星級和輸入框內容
  ngOnChanges(changes: SimpleChanges):void{
    this.stars = [];
    for(let i=1;i<=5;i++){
      this.stars.push(i>this
 
.rating)
    }
  }
//input裝飾器，星級評價的組件的rating屬性應該由他的父組件傳遞給它
  @Input()
  private rating:number = 0;

  @Output()
  private  ratingChange:EventEmitter<number> = new EventEmitter(); //這裏的名字一定要用屬性名+Change才能在父組件中使用[(rating)]進行雙向數據綁定

  private stars:boolean[];
  @Input()
  private readonly:boolean
 
 = true;

  constructor() { }

  ngOnInit() {
      
  }

  clickStar(index:number){
    if(!this.readonly){
     this.rating = index+1;
     this.ngOnInit();
      this.ratingChange.emit(this.rating);
     }
  }

}

父組件調用子組件，進行雙向數據綁定

<app-stars [(rating)]="newRating" [readonly]="false"></app-stars>

angular4 組件間通信