(九)、Angular4.0 依賴注入

一、注入器(從容器中獲取對象，相當於java中的@Autowired)(在組件的xxx.component.ts中使用)

constructor(private productService: ProductService){...}

二、提供器(把對象放入容器，相當於java中的@Component)(在app.module.ts -> @NgModule -> providers屬性中配置)，四種方式示例：

providers:[ProductService]

providers:[{provide:ProductService,userClass:ProductService}]

providers:[{provide:ProductService,useClass:AnotherProductService}]

providers:[{provide:ProductService,useFactory:() => {...}}]

三、創建一個di項目，用於angular依賴注入測試demo

ng new di --routing

四、新建一個組件 product1

ng g component product1

五、新建一個服務，在多個組件之間共享 product，放在shared文件夾下

ng g service shared/product

六、在product.service.ts中聲明一個Product對象和一個getProduct()函數

import { Injectable } from '@angular/core';

@Injectable()
export class ProductService {

  constructor() { }

  getProduct(): Product {
    return new Product(0, 'iphone7', 5899, '最新款');
  }

}

export class Product {
  constructor(public id: number,
              public title: string,
              public price: number,
              public desc: string){
  }
}

七、在app.module.ts中的providers屬性放入ProductService

providers: [ProductService]

八、修改product1.component.ts從容器中獲取對象

import { Component, OnInit } from '@angular/core';
import {Product, ProductService} from '../shared/product.service';

@Component({
  selector: 'app-product1',
  templateUrl: './product1.component.html',
  styleUrls: ['./product1.component.css']
})
export class Product1Component implements OnInit {

  // 聲明一個屬性獲取對象
  product: Product;

  // 從容器中注入對象
  constructor(private productService: ProductService) { }

  ngOnInit() {
    this.product = this.productService.getProduct();
  }

}

九、product1.component.html

<div>
  <h4>商品詳情</h4>
  <h6>名稱：{{product.title}}</h6>
  <h6>價格：{{product.price}}</h6>
  <h6>描述：{{product.desc}}</h6>
</div>

十、修改主模板app.component.html

<div>
  <div>
    <h3>基本的依賴注入樣例</h3>
  </div>
  <div>
    <app-product1></app-product1>
  </div>
</div>
<router-outlet></router-outlet>

十一、啓動項目，訪問localhost:4200

十二、使用工廠和值聲明提供器（根據條件new不同的對象）

  providers: [{
    provide: ProductService,
    useFactory: (logger:LoggerService, appConfig) => {
      if (appConfig.isDev) {
        return new ProductService(logger);
      }else {
        return new AnotherProductService(logger);
      }
    },
    deps: [LoggerService, 'IS_DEV_ENV']
  },
  LoggerService,
    {provide: 'APP_CONFIG', userValue: {isDev: false}}]