类型“ Observable <HttpEvent <any >>”上不存在属性“ do”

Question

此令牌拦截器服务出了什么问题？它显示错误： 属性“ do”在类型“ Observable>”上不存在。 在此行下：  返回next.handle（_req）.do（（event：HttpEvent）=> {

import { switchMap } from 'rxjs/operators';
import { TokenProvider } from './token/token';
import { Observable } from 'rxjs/Observable';
import { fromPromise } from 'rxjs/observable/fromPromise';
import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
  HttpEvent,
  HttpResponse,
  HttpErrorResponse
} from '@angular/common/http';
import {
  IonicPage,
  NavController,
  NavParams,
  AlertController,
  LoadingController
} from 'ionic-angular';


@Injectable()
export class TokenInterceptor implements HttpInterceptor {
  constructor(private tokenProvider: TokenProvider, public navCtrl: NavController) {}

  intercept(
    req: HttpRequest<any>,
    next: HttpHandler
  ): Observable<HttpEvent<any>> {
    return fromPromise(this.tokenProvider.GetToken()).pipe(
      switchMap(token => {
        const headersConfig = {
          'Content-Type': 'application/json',
          Accept: 'application/json'
        };
        if (token) {
          headersConfig['Authorization'] = `beader ${token}`;
        }
        const _req = req.clone({ setHeaders: headersConfig });
        return next.handle(_req).do((event: HttpEvent<any>) => {
      if (event instanceof HttpResponse) {
        // do stuff with response if you want
      }
    }, (err: any) => {
      if (err instanceof HttpErrorResponse) {
        if (err.status === 401) {
          this.navCtrl.push('LoginPage');
       ...

如果无法解决该错误，那么还有另一个选项可以用“ do”代替吗？