我注意到 Angular 不会将 Accept-Language 标头添加到请求中，我希望能够在后端检查语言。

我试图执行以下操作：

版本 1：

import { TranslateService } from '@ngx-translate/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from "@angular/common/http";
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

    constructor(
        private translateService: TranslateService
    ) {}

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        console.debug("Request intercepted by AuthInterceptor.");
        return next.handle(
            req.clone({
                headers: req.headers.append(
                    "Accept-Language", this.translateService.currentLang
                )
            })
        );      
    }
}

版本 2：

import { TranslateService } from '@ngx-translate/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from "@angular/common/http";
import { Injectable, Injector } from '@angular/core';
import { Observable } from 'rxjs';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

    constructor(
        private injector: Injector
    ) {}
    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        console.debug("Request intercepted by AuthInterceptor.");
        return next.handle(
            req.clone({
                headers: req.headers.append(
                    "Accept-Language", this.injector.get(TranslateService).currentLang
                )
            })
        );        
    }
}

但这些都不起作用。我假设 TranslateService 不能在这里使用，就像在组件中一样。如果是这样，那么我如何获取所选语言并在拦截器中使用它？

更新： 使用版本 1，我收到以下错误：

ERROR TypeError: Cannot read property 'length' of undefined
    at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.applyUpdate (http.js:200)
    at http.js:171
    at Array.forEach (<anonymous>)
    at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.init (http.js:171)
    at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.forEach (http.js:236)
    at Observable._subscribe (http.js:1436)
    at Observable.push../node_modules/rxjs/_esm5/internal/Observable.js.Observable._trySubscribe (Observable.js:43)
    at Observable.push../node_modules/rxjs/_esm5/internal/Observable.js.Observable.subscribe (Observable.js:29)
    at subscribeTo.js:21
    at subscribeToResult (subscribeToResult.js:11)