ngOnChanges不会被解雇

Question

我正在运行代码中测试ngOnChanges方法。但是似乎ngOnchanges并没有被调用，尽管它已经编译了。下面是我的代码。

create-Emploe.Component.html：

<form #employeeForm="ngForm"  (ngSubmit)=saveEmployee(employeeForm)>
  <div class="panel panel-primary">
    <div class="panel-heading">
      <h3 class="panel-title"> Create Employee</h3>
    </div>
    <div class="panel-body">
      <div class="form-group" [class.has-error]="fullName.invalid && fullName.touched" [class.has-success]="fullName.valid">
        <label for="fullName"class="control-label">Full Name</label>
        <input required type ="text"  class= "form-control" 
          name="fullName1" 
          [(ngModel)]="employee.fullName"
          #fullName="ngModel" id="fullName">
        <span class="help-block" *ngIf="fullName.invalid && fullName.touched">
          Full Name is Required
        </span>
      </div>
    </div>
    <div class="panel-footer">
     <button  [disabled]="employeeForm.invalid" type ="submit" class= "btn btn-primary" > Save </button>
    </div>
  </div>
  {{employeeForm.value|json}}
  employee: {{employee| json}}
  employee.isActive: {{employee.isActive}}
</form>

create-Emploe.Component.ts：

import { Component,OnChanges, OnInit ,SimpleChanges,Input} from '@angular/core';
import { NgForm } from '@angular/Forms';
import { Department } from '../models/department.model';
import { BsDatepickerModule,BsDatepickerConfig} from 'ngx-bootstrap/datepicker';
import { Employee } from '../models/employee.model';

@Component({
  selector: 'app-create-employee',
  templateUrl: './create-employee.component.html',
  styleUrls: ['./create-employee.component.css']
})
export class CreateEmployeeComponent implements OnInit, OnChanges {

  constructor() {}

  saveEmployee( employeeForm:NgForm): void {
    console.log(employeeForm);
    console.log("employee = " + JSON.stringify(this.employee));  
  }


  allMsgChangeLogs: string[] = [];
  allEmployeeChangeLogs: string[] = [];

  @Input() employee:Employee = { 
    id: null,
    fullName: 'Jay',
  }
  ngOnChanges(changes: SimpleChanges): void {
    console.log("inside on changes"); 
    for (let propName in changes) {  

      let change = changes[propName];

      let curVal  = JSON.stringify(change.currentValue);
      let prevVal = JSON.stringify(change.previousValue);
      let changeLog = `${propName}: currentValue = ${curVal}, previousValue = ${prevVal}`;

      if (propName === 'employee') {
          this.allEmployeeChangeLogs.push(changeLog);
          console.log(changeLog);
      } else {
         console.log("change detecetd");
      }
    }
  }

表单中使用的模型对象employee是: employee.model.ts：

export class Employee {
    id: number;
    fullName: string;
}

ngOnChanges方法根本不会被解雇。有什么建议吗？

Answer 1

@Input用于angular components之间的父子交互。我没有从您的代码中看出，您将employee传递给CreateEmployeeComponent。所以employee总是undefined，ngOnChanges不触发。更多信息在这里，https://angular.io/guide/component-interaction。