如何动态覆盖 Angular2 可注入服务？答案

【问题标题】：How do I dynamically overwrite an Angular2 Injectable Service?如何动态覆盖 Angular2 可注入服务？
【发布时间】：2016-10-15 17:57:21
【问题描述】：

我有一个可注入服务 HttpRequestService，我想在没有服务器时将其替换为 MockHttpRequestService，因为我在开发模式下运行 (npm start)。这个 MockHttpRequestService 会发回非常简单的响应。

我以为我找到了一种方法来动态替换我的 HttpRequestService，但不幸的是，我发现 HttpRequestService 仍在使用中。这是我尝试过的：

main.ts

import {bootstrap} from '@angular/platform-browser-dynamic';
import {provide} from '@angular/core';
import {ROUTER_PROVIDERS, Router} from '@angular/router-deprecated';
import {HashLocationStrategy, LocationStrategy} from '@angular/common'
import {Http, HTTP_PROVIDERS} from '@angular/http';
import {CORE_DIRECTIVES} from '@angular/common';
import {HttpRequestService} from './app/services/HttpRequestService';
import {MockHttpRequestService} from './app/services/MockHttpRequestService'
import {MyConfigInjectable} from './app/MyConfigInjectable';
import {SomeService} from './app/services/SomeService';

export function main(initialState?: any): Promise<any> {

    let providers = [
        ...HTTP_PROVIDERS,
        ...CORE_DIRECTIVES,
        ...ROUTER_PROVIDERS,
        provide(LocationStrategy, { useClass: HashLocationStrategy })
    ];

    if(process.env.ENV === 'development'){
        console.log('Is it set to development?'); //Yes. Yes it is.
        providers.push(MyConfigInjectable);
        providers.push(SomeService);
        providers.push(provide(HttpRequestService, {
            deps: [MyConfigInjectable, Http, SomeService, Router],
            useClass: MockHttpRequestService
        }));
    }

    return bootstrap(App, providers).catch(err => console.error(err));
}

MockHttpRequestService.ts

import {Injectable} from '@angular/core';
import {Http} from '@angular/http';
import {Router} from '@angular/router-deprecated';
import {SomeService} from './SomeService';
import {MyConfigInjectable} from '../MyconfigInjectable';

@Injectable()
export class MockHttpRequestService extends HttpRequestService {
    constructor(protected config: MyConfigInjectable,
                protected http: Http,
                protected someService: SomeService,
                protected router: Router) {
        super(config, http, someService, router);
    }

    post(url: string, body: string) {
        console.log('Are we getting here?'); //No. No we're not.
        //...
    }
}

【问题讨论】：

糟糕。非易失性。得到它的工作。我在我的 App.ts 组件中覆盖了新的提供程序。一旦我从 App.ts 的组件提供程序中删除了 HttpRequestService 并仅在 main.ts 中声明它，一切正常。除非有人反对，否则我可能会删除这个问题。

标签： angular npm mocking angular-ui-bootstrap

【解决方案1】：

您可以像这样在引导程序中使用 useClass 覆盖 Angular2 Service 可注入服务：

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

    const IS_ENV_DEV = true; //Put this constant in your config maybe

    bootstrap(App, [
      provide(RaceService, {useClass: IS_ENV_DEV ? MockHttpRequestService : HttpRequestService})
    ])

或直接在使用您的 http 服务的组件中

@Component({
   selector: 'my-comp',
   providers: [provide(HttpRequestService, {useClass: MockHttpRequestService})],
   template: `<strong>I use a mocked service</strong>`
})
export class MyComponent {

  constructor(private httpRequestService: HttpRequestService) {
    //Faker !
  }
}

我希望这个回复有帮助:)

【讨论】：