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我的父 Angular 组件有一个嵌套的子组件。该子组件是一个按钮列表。单击一个按钮时，会将一个值传递给子组件。然后该子组件会相应地更新为 id。我已经对孩子实施了一些变化检测。当孩子注册来自父母的更新时，它会运行 ngOnChanges 挂钩。在这里我调用我的后端并返回数据

我的代码工作正常，但它似乎是一个 hack。正如您在以下代码中看到的，我分离了 changeDetection 对象。在 ngOnChanges - 在订阅部分，我再次重新附加 cd。我不喜欢

你们能给我一些指示吗？

@Component({
  selector: 'app-challenge',
  templateUrl: './challenge.component.html',
  styleUrls: ['./challenge.component.css']
})
export class ChallengeComponent implements OnInit {
  @Input() focusedChallenge: string;

  eventId = {};
  challenge: Challenge;
  userSelection;

  constructor(
    public snackBar: MatSnackBar,
    private eventService: EventService,
    private activeRoute: ActivatedRoute,
    private cd: ChangeDetectorRef
  ) {  
this.cd.detach()
}

  ngOnInit() {
    this.eventId = this.activeRoute.snapshot.params.id;
  }

  ngOnChanges() {
    this.eventService.getChallenge(this.focusedChallenge)
      .subscribe(
        res => {
          this.cd.reattach();
          console.log(res)
          this.challenge = res
        },
        err => { console.log(err) }
      )
      challengeSelected.currentValue.toUpperCase();
  }

更新以响应答案

它确实为我提供了我想要的 ngOnChanges(changes: SimpleChanges) 结果。但它仍然给我们一个错误。说它是未定义的。

在此处输入图像描述

options 数组是 Challenge 上的嵌套数组

从 db 返回的对象

{_id: "5b86dc5bfb6fc03893e55001", shortEventId: "d2d3", organization: "Brædstrup", name: "1. december", winner: "", …}
born: "1. decemberplus andet"
endDate: "2018-10-06T23:59:00.000Z"
id: "5b86dc5bfb6fc03893e55001"
name: "1. december"
options: Array(4)
0: {name: "Matas", isCorrect: true, description: "Matas er den førende skib", image: "https://cityxpstorage.blob.core.windows.net/images/Matas.png", id: null}
1: {name: "Føtex", isCorrect: false, description: "Føtex er en dejlig butik", image: "https://cityxpstorage.blob.core.windows.net/images/Føtex.png", id: null, …}
2: {name: "Kvickly", isCorrect: false, description: "Kvickly er en dejlig butik", image: "https://cityxpstorage.blob.core.windows.net/images/Matas.png", id: null, …}
3: {name: "MC Jørgensen", isCorrect: false, description: "MC Jørgensen er en dejlig butik", image: "https://cityxpstorage.blob.core.windows.net/images/Matas.png", id: null}
length: 4
__proto__: Array(0)
organization: "Brædstrup"
shortEventId: "d2d3"
startDate: "2018-10-06T00:00:00.000Z"
winner: ""
_id: "5b86dc5bfb6fc03893e55001"
__proto__: Object
4

1 回答 1

2

由于您使用的是字符串类型输入，因此您不需要捕获任何 ChangeDetection。因此，只要值发生变化，最好删除ChangeDetectorRef并让角度触发该ngOnChanges方法。@Input

您的代码应为 -

@Component({
  selector: 'app-challenge',
  templateUrl: './challenge.component.html',
  styleUrls: ['./challenge.component.css']
})
export class ChallengeComponent implements OnInit {
  @Input() focusedChallenge: string;

  eventId = {};
  challenge: Challenge;
  userSelection;

  constructor(
    public snackBar: MatSnackBar,
    private eventService: EventService,
    private activeRoute: ActivatedRoute
  ) {  
}

  ngOnInit() {
    this.eventId = this.activeRoute.snapshot.params.id;
  }

ngOnChanges(changes: SimpleChanges) {

    let newFocusedChallenge  = changes["focusedChallenge"].currentValue;

    this.eventService.getChallenge(newFocusedChallenge)
      .subscribe(
        res => {
          console.log(res)
          this.challenge = res;
          //challengeSelected.currentValue.toUpperCase(); //not sure if is required
        },
        err => { console.log(err) }
      )
  }
}
于 2018-10-13T08:34:33.167 回答