Angular 2依赖注入

Question

我将为我的数据服务创建一个基类。我把像post，get，异常处理这样的常用函数放在基类中。派生类只需要继承基类，而不需要Http或仅在基类中使用的必要内容，基类需要自己“解析”它的依赖关系。

import { Injectable, ReflectiveInjector } from '@angular/core'
import { Http, RequestOptions, Headers, Request, Response } from '@angular/http';
import { Observable } from 'rxjs';

export class DataServiceBase{
    private _injector: ReflectiveInjector;
    private get injector() : ReflectiveInjector{
        if(this._injector == null)
            this._injector = ReflectiveInjector.resolveAndCreate([Http]);

        return this._injector;
    }

    private _http: Http;
    private get http(): Http{
        if(this._http == null)
            this._http = this.injector.get(Http);

        return this._http;
    }

    private extractData(res: Response) {
        let body = res.json();
        return body || {};
    }

    private handleException(exception: any) {
        console.error(exception);
        return Observable.throw(exception.statusText);
    }

    protected post(url: string, data: any): Observable<any> {
        var headers = new Headers({ 'Content-Type': 'application/json' });
        var options = new RequestOptions({ headers: headers });

        var body = JSON.stringify(data);

        return this.http.post(url, body, options)
            .map(this.extractData)
            .catch(this.handleException);
    }

    protected get(url: string) : Observable<any> {
        return this.http.get(url)
            .map(this.extractData)
            .catch(this.handleException);
    }
}

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

import { TodoItem } from '../model/todoItem';

import { DataServiceBase } from './dataServiceBase';

@Injectable()
export class ValidationSampleService extends DataServiceBase{
    constructor(){
        super();
    }

    public getAllTodoItem(): Observable<any>{
        return this.get('/api/todo');
    }

    public updateToDoItem(item: any){
        return this.post('/api/todo/updateTodoItem', item);
    }
}

但是我收到了一个异常，比如"No provider for Http"，你能告诉我会错过哪一个吗？

如果我在构造器中注入服务，一切都可以正常工作。

​

​

Answer 1

如果子类没有显式的构造函数，则使用超类的构造函数：

export class DataServiceBase{
  constructor(private http:Http){}

export class ValidationSampleService extends DataServiceBase{
    // constructor(){
    //    super();
    // }

另请参阅

• Inject Http manually in angular 2
• Access @angular/http Http Client from Plain Ol' TypeScript Class