Angular 依赖注入

2018-08-11 本文已影响149人 JustTheSame

Angular 依赖注入

依赖注入：Dependency Injection 简称DI

控制反转：Inversion of Control 简称IOC

var product = new Product();
createShipment(product);

var product = new MockProduct();
createShipment(product);

通过手工的实例化对象。

依赖注入的好处

@NgModule({
    providers: [ProductService]
    = providers: [{provide: ProductService, useClass: ProductService}]
    = providers: [{provide: ProductService, useClass: AnotherProductService}]//这样切换项目对于ProductComponent不需要修改。
})
export class AppModule {}

@Component({
    ...省略组件配置
})
export class ProductComponent {
    product: Product;
    constructor(productService: ProductService) {//需要ProductService的Token，即上方provide对应的值。
        this.product = productService.getProduct();
    }
}

依赖注入

注入器constructor(private productService: ProductService){}
提供器providers: [ProductService]，providers: [{provide: ProductService, useClass: ProductService}]还可以使用工厂方法返回实例providers: [{provide: ProductService, userFactory: () => {...}}]

生成组件和服务，分别使用指令：ng g component product1和ng g service shared/product

首先定义商品信息类

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

@Injectable({
  providedIn: 'root'
})
export class ProductService {

  constructor() {
  }
}

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

并且编写getProduct()方法

getProduct(): Product {
    return new Product(0, 'Iphone7', 5999, '最新款手机');
}

然后去修改模块的声明app.module.ts，添加ProductService

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';
import { Product1Component } from './product1/product1.component';
import {ProductService} from './shared/product.service';

@NgModule({
  declarations: [
    AppComponent,
    Product1Component
  ],
  imports: [
    BrowserModule
  ],
  providers: [ProductService],
  bootstrap: [AppComponent]
})
export class AppModule { }

修改Product1Component并且注入ProductService

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 {

  product: Product;

  constructor(private productService: ProductService) {
  }

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

}

跟着修改页面模版内容，展示获取的product内容。

<div>
  <h1>商品详情</h1>
  <h2>名称：{{product.title}}</h2>
  <h2>价格：{{product.price}}</h2>
  <h2>描述：{{product.desc}}</h2>
</div>

提供器的作用域

提供器除了可以声明在模块中，也可以声明在组件中。我们在创建第二个组件和另外一个服务，分别使用指令：ng g component product2和ng g service shared/anotherProduct

我们使用AnotherProductService实现ProductService并实现其中方法

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

@Injectable({
  providedIn: 'root'
})
export class AnotherProductService implements ProductService{

  constructor() { }

  getProduct(): Product {
    return new Product(0, 'Iphone9', 6999, '最新款手机');
  }
}

然后修改product2.component.ts，直接复制product1.component.ts代码即可，不同的地方是在组件的级别使用providers

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

@Component({
  selector: 'app-product2',
  templateUrl: './product2.component.html',
  styleUrls: ['./product2.component.css'],
  providers: [{
    provide: ProductService, useClass: AnotherProductService
  }]
})
export class Product2Component implements OnInit {

  product: Product;

  constructor(private productService: ProductService) {
  }

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

}

跟着修改页面模版内容，展示获取的product内容，其实与product1组件页面模版一样。

<div>
  <h1>商品详情</h1>
  <h2>名称：{{product.title}}</h2>
  <h2>价格：{{product.price}}</h2>
  <h2>描述：{{product.desc}}</h2>
</div>

这样product1是获取ProductService注入的信息，而product2是获取AnotherProductService注入的信息。

总结：

当一个提供器声明在模块上，它是对所有组件可见的，所有组件都是可以使用的。
当一个提供器声明在组件中，它只对组件以及其子组件可见，其他组件不可以注入它。
当模块中的提供器和组件中的提供器重名时，声明在组件中的提供器会覆盖声明在模块中的提供器，这时使用的是声明在组件中的提供器。
一般情况下，优先将服务器供器声明在模块中。

@Injectable()决定着其构造函数中能不能注入别的服务。只有声明为@Injectable()的服务才可以注入其它的服务。

服务之间互相注入

首先生成新的服务ng g service shared/logger

这个服务比较简单，即输出日志到控制台。

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

@Injectable({
  providedIn: 'root'
})
export class LoggerService {

  constructor() {
  }

  log(message: string) {
    console.log(message);
  }
}

将LoggerService注入到ProductService中去。

product.service.ts

import {Injectable} from '@angular/core';
import {LoggerService} from './logger.service';

@Injectable({
  providedIn: 'root'
})
export class ProductService {

  constructor(private logger: LoggerService) {
  }

  getProduct(): Product {
    this.logger.log('getProduct方法被调用');
    return new Product(0, 'Iphone7', 5999, '最新款手机');
  }
}

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

想要注入LoggerService，必须在模块中声明这个提供器。

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';
import { Product1Component } from './product1/product1.component';
import {ProductService} from './shared/product.service';
import { Product2Component } from './product2/product2.component';
import {LoggerService} from './shared/logger.service';

@NgModule({
  declarations: [
    AppComponent,
    Product1Component,
    Product2Component
  ],
  imports: [
    BrowserModule
  ],
  providers: [ProductService, LoggerService],
  bootstrap: [AppComponent]
})
export class AppModule { }

为什么组件没有@Injectable()装饰器也能注入服务呢。其实@Component是其的子类。

使用工厂和值声明提供器

修改模版中提供器的声明

import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';

import {AppComponent} from './app.component';
import {Product1Component} from './product1/product1.component';
import {ProductService} from './shared/product.service';
import {Product2Component} from './product2/product2.component';
import {LoggerService} from './shared/logger.service';
import {AnotherProductService} from './shared/another-product.service';

@NgModule({
  declarations: [
    AppComponent,
    Product1Component,
    Product2Component
  ],
  imports: [
    BrowserModule
  ],
  providers: [{
    provide: ProductService,
    useFactory: () => {
      let logger = new LoggerService();
      let dev = Math.random() > 0.5;
      if (dev) {
        return new ProductService(logger);
      } else {
        return new AnotherProductService(logger);
      }
    }
  }, LoggerService],
  bootstrap: [AppComponent]
})
export class AppModule {
}

但此时ProductService依赖于LoggerService，做一些调整

import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';

import {AppComponent} from './app.component';
import {Product1Component} from './product1/product1.component';
import {ProductService} from './shared/product.service';
import {Product2Component} from './product2/product2.component';
import {LoggerService} from './shared/logger.service';
import {AnotherProductService} from './shared/another-product.service';

@NgModule({
  declarations: [
    AppComponent,
    Product1Component,
    Product2Component
  ],
  imports: [
    BrowserModule
  ],
  providers: [{
    provide: ProductService,
    useFactory: (logger: LoggerService) => {
      let dev = Math.random() > 0.5;
      if (dev) {
        return new ProductService(logger);
      } else {
        return new AnotherProductService(logger);
      }
    },
    deps: [LoggerService]
  }, LoggerService],
  bootstrap: [AppComponent]
})
export class AppModule {
}

使用值做判断

import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';

import {AppComponent} from './app.component';
import {Product1Component} from './product1/product1.component';
import {ProductService} from './shared/product.service';
import {Product2Component} from './product2/product2.component';
import {LoggerService} from './shared/logger.service';
import {AnotherProductService} from './shared/another-product.service';

@NgModule({
  declarations: [
    AppComponent,
    Product1Component,
    Product2Component
  ],
  imports: [
    BrowserModule
  ],
  providers: [{
    provide: ProductService,
    useFactory: (logger: LoggerService, isDev) => {
      let dev = Math.random() > 0.5;
      if (isDev) {
        return new ProductService(logger);
      } else {
        return new AnotherProductService(logger);
      }
    },
    deps: [LoggerService, 'IS_DEV_ENV']
  }, LoggerService, {
    provide: 'IS_DEV_ENV', useValue: false
  }],
  bootstrap: [AppComponent]
})
export class AppModule {
}

也可以使用值对象

import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';

import {AppComponent} from './app.component';
import {Product1Component} from './product1/product1.component';
import {ProductService} from './shared/product.service';
import {Product2Component} from './product2/product2.component';
import {LoggerService} from './shared/logger.service';
import {AnotherProductService} from './shared/another-product.service';

@NgModule({
  declarations: [
    AppComponent,
    Product1Component,
    Product2Component
  ],
  imports: [
    BrowserModule
  ],
  providers: [{
    provide: ProductService,
    useFactory: (logger: LoggerService, appConfig) => {
      let dev = Math.random() > 0.5;
      if (appConfig.isDev) {
        return new ProductService(logger);
      } else {
        return new AnotherProductService(logger);
      }
    },
    deps: [LoggerService, 'APP_CONFIG']
  }, LoggerService, {
    provide: 'APP_CONFIG', useValue: {isDev: false}
  }],
  bootstrap: [AppComponent]
})
export class AppModule {
}

注入器的层级关系

应用级注入器=>主组件注入器=>子组件注入器

app.module.ts=>app.component.ts=>product.component.ts

会根据构造函数的参数注入进来。

手工注入方式，实际过程中要避免使用这种写法。

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

@Component({
  selector: 'app-product2',
  templateUrl: './product2.component.html',
  styleUrls: ['./product2.component.css'],
  // providers: [{
  //   provide: ProductService, useClass: AnotherProductService
  // }]
})
export class Product2Component implements OnInit {

  product: Product;

  private productService: ProductService;

  constructor(private injector: Injector) {
    this.productService = injector.get(ProductService);
  }

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

}

Angular 依赖注入

Angular 依赖注入

依赖注入的好处

依赖注入

提供器的作用域

服务之间互相注入

使用工厂和值声明提供器

注入器的层级关系

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