angular 2(click)传递迭代变量和[class.selected]传递函数

Question

以下内容摘自ng-book 2

  @Component({
  selector: 'products-list',
  directives: [ProductRow],
  inputs: ['productList'],
  outputs: ['onProductSelected'],
  template: `
  <div class="ui items">
    <product-row 
      *ngFor="let myProduct of productList" 
      [product]="myProduct" 
      (click)='clicked(myProduct)'
      [class.selected]="isSelected(myProduct)">
    </product-row>
  </div>
  `
})
class ProductsList {
  /**
   * @input productList - the Product[] passed to us
   */
  productList: Product[];

  /**
   * @ouput onProductSelected - outputs the current 
   *          Product whenever a new Product is selected
   */
  onProductSelected: EventEmitter<Product>;

  /**
   * @property currentProduct - local state containing 
   *             the currently selected `Product`
   */
  currentProduct: Product;

  constructor() {
    this.onProductSelected = new EventEmitter();
  }

  clicked(product: Product): void {
    this.currentProduct = product;
    this.onProductSelected.emit(product);
  }

  isSelected(product: Product): boolean {
    if (!product || !this.currentProduct) {
      return false;
    }
    return product.sku === this.currentProduct.sku;
  }

}

@Component({
  selector: 'product-row',
  inputs: ['product'],
  ... not relevant to the question
  `
})
class ProductRow {
  product: Product;
}

两个问题,

Q1.在哪里说

(click)='clicked(myProduct)'

是否与ProductRow组件上的产品属性相同的参数？我习惯将$ event传递给clicked.为什么要传递"myProduct"呢？

Q2.在哪里说

[class.selected]="isSelected(myProduct)"

好像我们正在做

[class.selected]="false"

对于所有产品,因为最初没有选择它们.角度如何能够一次又一次地调用isSelected(myProduct)？角度如何决定何时调用isSelected？

Answer 1

parent-child这是Angular2 中的通信示例。

当您使用(click)='clicked(myProduct)'事件时，您本质上所做的是emitting使用属性来获取所选产品的值 @ouput onProductSelected，如下所示：

this.onProductSelected.emit(product);
$event` here would be equivalent to `#myProduct.value

当任何事件被执行时，Angular2 的变化检测就会启动；检查所有模板表达式值。然后，它根据值的变化更新属性绑定。现在每次值发生myProduct变化时，属性绑定都[class.selected]需要更新，因此isSelected方法会被调用。