Angular 2 – 在管道中调用服务

有一种方法可以在管道中注入和调用服务吗？我有货币服务,我想用它来获取基于id的名称.
谢谢！！

这是我的代码：

@Pipe({name: 'currencypipe',pure: false})
export class CurrencyPipe implements PipeTransform {
    symbol: string = null;

    constructor(private currencyService: CurrencyService) {

    }

    transform(value: number,currencyId: number): Promise<String> {
        return this.currencyService.getCurrencie(currencyId).then(response => {
                return (value + " " + response.symbol);
            }
        );
    }
}

我就是这样用的

{{3 | currencypipe: 2 | async}}

解决方法

您可以像在任何组件中那样在管道中注入服务,

@Pipe({
    name: 'my-currency-pipe'
})
export class MyCurrencyPipe implements PipeTransform {
    constructor(service: SomeService) {

    }

    transform(value: string): string {
        return value;
    }
}

但是,您也可以在管道中使用参数. Read more here.

更新

excerpts from Pipe documentation搜索不纯的缓存管,

Let’s write one more impure pipe,a pipe that makes an HTTP request to
the server. normally,that’s a horrible idea. It’s probably a horrible
idea no matter what we do. We’re forging ahead anyway to make a point.
Remember that impure pipes are called every few microseconds. If we’re
not careful,this pipe will punish the server with requests.

牢记这一点,您可以在下面针对您的场景进行异步获取结果,

import { Component,PipeTransform,Pipe } from '@angular/core';

export class CurrencyService  {
  getCurrencie(currencyId):Promise<string> {
     return new Promise<any>((resolve,reject) => {
       setTimeout(() => {
         if(currencyId === 1 ){
            resolve({symbol : '$'});
         }else{
           resolve({symbol: '£'});
         }
       },1000)
     })
  }
}

@Pipe({name: 'currencypipe',pure: false})
export class CurrencyPipe implements PipeTransform {
    symbol: string = null;
    prevalue: string = null;
    result: string = '';

    constructor(private currencyService: CurrencyService) {
    }

    transform(value: number,currencyId: number) {
      if (value !== this.prevalue) {
         this.prevalue = value;
         this.result = '';

         this.currencyService.getCurrencie(currencyId).then(response => {                   
                this.result = value + " " + response.symbol;
            }
        );
      }
       return this.result;
    }
}


@Component({
  selector: 'my-app',template: `<h1>Currency Pipe</h1>
   <hr />
   {{3 | currencypipe: 1 }}
  `
})
export class AppComponent { }

@NgModule({
  imports:      [ browserModule ],declarations: [ AppComponent,CurrencyPipe ],providers: [ CurrencyService ],bootstrap:    [ AppComponent ]
})

export class AppModule { }

这是Plunker !!

希望这可以帮助！！