Angular 4 HttpInterceptor：显示和隐藏加载器

我想在创建请求时显示加载程序,并在收到响应时隐藏该加载程序.

虽然代码波纹管在检测到HttpResponse时起作用,但它没有检测到Http Failure(当响应代码不同于200时),因此加载器不会被隐藏.

@Injectable()
export class AuthInterceptor implements HttpInterceptor {
constructor(private loaderService: LoaderService) { }

intercept(req: HttpRequest<any>,next: HttpHandler): Observable<HttpEvent<any>> {

    this.loaderService.show();

    return next
        .handle(req)
        .do(event => {
            //nothing is printed when a Http failure occurs
            console.log('detecting event ',event);
            if (event instanceof HttpResponse) {
                console.log('detecting http response');
                this.loaderService.hide();
            }
        });
  }
}