Angular 4 @Input() 值在 ngOnInit() 中未定义

Question

month-detail.component.html

import ...
@Component({
  template: `{{month?.id}} <app-month-date [month]="month"></app-month-date>`
})
export class MonthDetailComponent implements OnInit {
  month: Month;
  ngOnInit(): void {
    this.route.params
      .switchMap((params: Params) => this.monthService.getMonth(+params["id"]))
      .subscribe(month => (this.month = month));
  }
}

month-date.component.html

<p>month-date works! {{month?.id}}</p>

month-date.component.ts

import { Component, OnInit, Input } from "@angular/core";
import { Month } from "app/attendance/month";

@Component({
  selector: "app-month-date",
  ...
})
export class MonthDateComponent implements OnInit {
  @Input() month: Month;
  ngOnInit() {
    //undefined --- here
    console.log(this.month);
  }}

month?.id 在 month-detail.component.html 中正确显示，但在 month-date 中使用标记 app-month-date 未定义月份.component.ts。 可能无法获取 ngOnInit 的值？

Answer 1

您可以通过在父模板中包含 *ngIf 来确保在将月份输入值发送给子组件之前未初始化子组件来解决此问题:

@Component({
  template: `{{month?.id}} <app-month-date *ngIf="month" [month]="month"></app-month-date>`
})