Angular 变量值在拦截方法-HTTP拦截器中不可见

我试图使用HTTP拦截器在HTTP请求的头中传递变量值。但这并没有发生

我已尝试将变量从AppComponent传递到服务。我可以看到变量值，但在Intercept方法下的同一服务中，我无法看到

import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent, HttpHeaders, HttpErrorResponse } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable, throwError } from 'rxjs';
import { catchError, retry } from 'rxjs/operators';
import * as $ from 'jquery';


@Injectable({
  providedIn:'root'
}) 
export class AppInterceptorService implements HttpInterceptor{

  etag : string
  headers : HttpHeaders

constructor() {}
getEtag(etag : string) {

  if(etag) {
    this.etag = etag;
    console.log("Etag from Interceptor :"+ this.etag)
   }
   else {
     this.etag = '*'
   }

}

handleError(error : HttpErrorResponse) {
    console.log("Error Occured")
    return throwError(error)
}

intercept(req: HttpRequest<any>, next: HttpHandler,): Observable<HttpEvent<any>> {
console.log("interceptetag : " + this.etag)

if(req.method === "GET"){
  this.headers = new HttpHeaders ({
    'Content-Type'    : 'application/json;odata=verbose',
    'Accept'          : 'application/json;odata=verbose',
    'X-RequestDigest' : $("#__REQUESTDIGEST").val(),
    'X-HTTP-Method': 'MERGE',
    'IF-MATCH': "40",

  })
}

if(req.method === "POST"){
  console.log("Etag form POST :"+this.etag)
  this.headers = new HttpHeaders ({
    'Content-Type'    : 'application/json;odata=verbose',
    'Accept'          : 'application/json;odata=verbose',
    'X-RequestDigest' : $("#__REQUESTDIGEST").val(),
    'X-HTTP-Method': 'MERGE',
    'IF-MATCH': this.etag,

  })
}


  const clone = req.clone({'headers' : this.headers})

    return next.handle(clone)
    .pipe(
        retry (1),
        catchError(this.handleError)
    )
}


}

应用模块

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { ReactiveFormsModule,FormsModule } from '@angular/forms';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
import { AppComponent } from './app.component';
import { SharePointService } from './services/sharepointservice.service';
import { AppInterceptorService } from './services/app-interceptor.service';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    ReactiveFormsModule,
    FormsModule,
    HttpClientModule

  ],
  providers: [SharePointService, 
              {'provide' : HTTP_INTERCEPTORS,
               'useClass' : AppInterceptorService,
                'multi' : true}],

  bootstrap: [AppComponent]
})
export class AppModule { }

---

根据，intercept有一个返回类型

Observable，根据，intercept有一个返回类型
Observable我忘了在帖子中提到这一点。我使用了返回类型。这是否解决了您的问题？如果没有，你还面临什么问题？查看上面正在工作的Stackblitz，看看你是否遗漏了什么。谢谢Nash！我看到了你的代码&它与我在应用程序中使用的代码相同。我不明白为什么这不起作用！它在截取方法中显示为未定义。我忘了在帖子中提到这一点。我使用了返回类型。这是否解决了您的问题？如果没有，你还面临什么问题？查看上面正在工作的Stackblitz，看看你是否遗漏了什么。谢谢Nash！我看到了你的代码&它与我在应用程序中使用的代码相同。我不明白为什么这不起作用！它在intercept方法中显示为未定义
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { ReactiveFormsModule,FormsModule } from '@angular/forms';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
import { AppComponent } from './app.component';
import { SharePointService } from './services/sharepointservice.service';
import { AppInterceptorService } from './services/app-interceptor.service';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    ReactiveFormsModule,
    FormsModule,
    HttpClientModule

  ],
  providers: [SharePointService, 
              {'provide' : HTTP_INTERCEPTORS,
               'useClass' : AppInterceptorService,
                'multi' : true}],

  bootstrap: [AppComponent]
})
export class AppModule { }


intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
  console.log("interceptetag : " + this.etag) 
  return new Observable<any>();
}