Angular4 第四章 依賴注入實戰
阿新 • • 發佈:2019-02-02
建立服務的命令:ng g service shared/stock ,生成了stockService的服務,需要宣告該服務的提供器
建立元件stock : ng g component stock
1.依賴注入,提供器宣告在模組中
(1)編寫服務提供器。shared\stock.service.ts 編寫一個股票資訊類,和一個getProduct方法,
(2)編寫注入器。stock\stock.component.ts中呼叫服務類StockService中getStock()方法import { Injectable } from '@angular/core'; @Injectable() export class StockService { constructor() { } getStock():Stock{ return new Stock(1,'IBM'); } } export class Stock{ constructor(public id :number,public name:string){ } }
(3)宣告提供器。app.component.ts加入import { Component, OnInit } from '@angular/core'; import { StockService, Stock } from '../shared/stock.service'; @Component({ selector: 'app-stock', templateUrl: './stock.component.html', styleUrls: ['./stock.component.css'] }) export class StockComponent implements OnInit { private stock:Stock; constructor(public stockService:StockService) { } ngOnInit() { this.stock=this.stockService.getStock(); } }
providers: [StockService],
上述程式碼是將提供器宣告在模組中,提供器也可以宣告在元件中
建立新元件stock2
建立新服務shared/anotherStock
2 依賴注入,提供器宣告在元件中
(1)編寫服務提供器。shared\another-stock.service.ts 中的AnotherStockService繼承了StockService,需要實現StockService中方法getStock()
(2)編寫注入器和宣告提供器。stock2\stock2.component.ts中,將提供器宣告在組建中,並呼叫AnotherStockService中的getStock()方法import { Injectable } from '@angular/core'; import { StockService, Stock } from './stock.service'; @Injectable() export class AnotherStockService implements StockService { getStock(): Stock { return new Stock(2,'微軟'); } constructor() { } }
import { Component, OnInit } from '@angular/core';
import { StockService, Stock } from '../shared/stock.service';
import { AnotherStockService } from '../shared/another-stock.service';
@Component({
selector: 'app-stock2',
templateUrl: './stock2.component.html',
styleUrls: ['./stock2.component.css'],
providers:[{provide:StockService,useClass:AnotherStockService}]
})
export class Stock2Component implements OnInit {
private stock:Stock;
constructor(private stockService:StockService) { }
ngOnInit() {
this.stock=this.stockService.getStock();
}
}
3.提供器的作用域
(1)提供器宣告模組中,對所有元件可見,所有元件都可以注入
(2)提供器宣告在元件,只對宣告他的元件和其子元件可見,其他元件不可以注入他
(3)當宣告在模組中提供器的token和宣告在元件中token一樣時,那麼元件中的提供器會覆蓋模組中的提供器
(4)優先將提供器宣告在模組中,只有提供器對某些元件不可見時,才將提供器宣告在元件中
@Injectable()//表示當前服務StockService的建構函式可以注入其他服務 @Component()繼承@Injectable4.服務注入服務
新建服務logger,原服務stockService,在StockService中注入LoggerService
(1)提供器編寫LoggerService
import { Injectable } from '@angular/core';
@Injectable()
export class LoggerService {
constructor() { }
log(message:string){
console.log(message);
}
}
(2)在StockService中注入LoggerService,並呼叫LoggerService中的log()方法import { Injectable } from '@angular/core';
import { LoggerService } from './logger.service';
@Injectable() //表示當前服務StockService的建構函式可以注入其他服務
export class StockService {
constructor(public logger:LoggerService) { }
getStock():Stock{
this.logger.log("getStock方法被呼叫");
return new Stock(1,'IBM');
}
}
export class Stock{
constructor(public id :number,public name:string){
}
}
(3)在模組中宣告LoggerService
providers: [StockService,LoggerService],
(4)因為AnotherStockService繼承了StockService,所以AnotherStockService也必須注入LoggerServiceimport { Injectable } from '@angular/core';
import { StockService, Stock } from './stock.service';
import { LoggerService } from './logger.service';
@Injectable()
export class AnotherStockService implements StockService {
constructor(public logger:LoggerService) { }
getStock(): Stock {
return new Stock(2,'微軟');
}
}