angular – 未定义标识符’required’. ‘__type’不包含此类成

产品form.component.html

<div class="row">

  <div class="col-md-6">
      <form #form="ngForm" (ngSubmit)="save(form.value)">

            <div class="form-group">
              <label for="title">Title</label>
              <input #title="ngModel" [(ngModel)]="product.title" name="title" id="title" type="text" class="form-control" required>
              <div class="alert alert-danger" *ngIf="title.touched && title.invalid">
                Title is required.
              </div>
            </div>

            <div class="form-group">
                <label for="price">Price</label>
                <div class="input-group">
                  <span class="input-group-addon">$</span>
                  <input #price="ngModel" ngModel [(ngModel)]="product.price" name="price" id="price" type="number" class="form-control" required [min]="0">
                </div>
                <div class="alert alert-danger" *ngIf="price.touched && price.invalid">
                  <div *ngIf="price.errors.required">Price is required.</div>
                  <div *ngIf="price.errors.min">Price should be 0 or higher.</div>
                </div>
            </div>

            <div class="form-group">
                <label for="category">Category</label>
                <select #category="ngModel" ngModel [(ngModel)]="product.category" name="category" id="category" class="form-control" required>
                  <option value=""></option>
                  <option *ngFor="let category of categories$| async" [value]="category.key">{{ category.payload.val().name }}</option>
                </select>
                <div class="alert alert-danger" *ngIf="category.touched && category.invalid">
                  Category is required.
                </div>
            </div>

            <div class="form-group">
                <label for="imageUrl">Image URL</label>
                <input #imageUrl="ngModel" ngModel [(ngModel)]="product.imageUrl" name="imageUrl" id="imageUrl" type="text" class="form-control" required url>
                <div class="alert alert-danger" *ngIf="imageUrl.touched && imageUrl.invalid">
                  <div *ngIf="imageUrl.errors.required">Image URL is required.</div>
                  <div *ngIf="imageUrl.errors.url">Please enter a valid URL.</div>
                </div>
            </div>

            <button class="btn btn-primary">Save</button>

          </form>
  </div>

  <div class="col-md-6">
      <div class="card" style="width: 20rem;">
          <img class="card-img-top" [src]="product.imageUrl" *ngIf="product.imageUrl">
          <div class="card-block">
            <h4 class="card-title">{{ product.title }}</h4>
            <p class="card-text">{{ product.price | currency: 'USD': symbol }}</p>
          </div>
        </div>
  </div>

</div>

产品form.component.ts

import { Component,OnInit } from '@angular/core';
import { CategoryService } from '../../category.service';
import { ProductService } from '../../product.service';
import { Router } from '@angular/router';
import { ActivatedRoute } from '@angular/router';
import 'rxjs/add/operator/take';

@Component({
  selector: 'app-product-form',templateUrl: './product-form.component.html',styleUrls: ['./product-form.component.css']
})
export class ProductFormComponent implements OnInit {

  categories$;
  product: any = {};

  constructor(
    private router: Router,private route: ActivatedRoute,private categoryService: CategoryService,private productService: ProductService) {
    this.categories$= categoryService.getCategories();

    let id = this.route.snapshot.paramMap.get('id');
    if (id) {
      this.productService.get(id).take(1).subscribe(p => this.product = p);
    }
  }

  save(product) {
    this.productService.create(product);
    this.router.navigate(['/admin/products']);
  }

  ngOnInit() {
  }

}

如何删除此错误？应用程序中的功能似乎没有受到影响.所以根据我的理解,它编译成有效的JS.我能够通过将其声明为“任何”来修复对象

如果可能的话,我有兴趣学习如何为此设置接口.