Javascript 角度服务返回具有未定义值的可观测值

我有一个angular应用程序，它应该在对服务器进行API调用后显示一组组件，服务器将使用用户可以根据其配置文件访问的组件进行响应

我使用一个单独的服务来处理和检索用户组件，并将其存储在服务本身中，以便在webapp中轻松获取

我的执行情况如下：

API服务进行API调用

api.service.ts

import { Injectable } from '@angular/core';
import {HttpClient, HttpParams} from '@angular/common/http';
import {AuthService} from './auth.service';
import {Params} from '@angular/router';
@Injectable({
  providedIn: 'root'
})


export class ApisService {

  GET_BATCH_SCHEDULE = 'http://localhost:8000/getbatchplan';
  GET_USER_STATIONS = 'http://localhost:7071/api/getUserStations';
  GET_USER_LOCATIONS = 'http://localhost:7071/api/getUserLocations';




  constructor(private httpClient: HttpClient, private authService: AuthService) { }


  getCutplanBatches() {
    return this.httpClient.get(this.GET_BATCH_SCHEDULE);
  }


  getStations(location: string) {
    if (location === undefined){
      console.log("undefined location call");
      location = 'aqua';
    }
    const params = new HttpParams()
      .set('email', this.authService.getAuthenticateduserInfo().displayableId)
      .append('location', location);

    return this.httpClient.get(this.GET_USER_STATIONS, { params: params });

  }

  getLocations() {
    const params = new HttpParams()
      .set('email', this.authService.getAuthenticateduserInfo().displayableId);

    return this.httpClient.get(this.GET_USER_LOCATIONS, { params: params });

  }


}

import {Injectable} from '@angular/core';
import {ApisService} from './apis.service';
import {StationModel} from '../models/station.model';
import {BehaviorSubject, Observable} from 'rxjs';


@Injectable({
  providedIn: 'root'
})


export class StationService {
  userStations: BehaviorSubject<StationModel[]>;
  userLocation: string;

  constructor(private apiService: ApisService) {
    this.userStations = new BehaviorSubject<StationModel[]>([]);
    this.setLocationStations('aqua');

  }
  setLocation(location: string) {
    this.userLocation = location;

  }
  getLocation() {

      return this.userLocation;


  }
  setLocationStations(locationSelect: string) {
    this.apiService.getStations(locationSelect).subscribe((data: StationModel[]) => {
      this.userStations.next(data['stations']);
      console.log('setting user locations:', this.userStations);
      return this.userStations;

    });


  }
  public getLocationStations(): Observable<StationModel[]> {
    console.log('inside station service:', this.userStations);
    console.log('inside station service loc:', this.userLocation);


    return this.userStations.asObservable();

  }

}

import {ActivatedRouteSnapshot, Resolve, RouterStateSnapshot} from '@angular/router';
import {Observable} from 'rxjs';
import {StationService} from '../../services/station.service';
import {Injectable} from '@angular/core';
import {StationModel} from '../../models/station.model';
@Injectable({
  providedIn: 'root'
})
export class StationRouteResolver implements Resolve<StationModel> {
  currentStation: StationModel;
  constructor(private stationService: StationService) {}

  resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
    console.log('Resolves:', route.params['location']);

    if (this.stationService.getLocation() === undefined) {
      console.log('Initial setting:', route.params['location']);
      this.stationService.setLocation(route.params['location']);

    }else if (this.stationService.getLocation() !== route.params['location']) {
      console.log('Changing location settings:', route.params['location']);
      this.stationService.setLocation(route.params['location']);
    }else{
      console.log('Same location found!');
    }

    this.stationService.getLocationStations().subscribe((stations: StationModel[]) => {
      console.log('observer resolver:', stations);

      this.currentStation = stations.filter((station) => {
        return station.stationPath === route.params['station'];

      })[0];
      console.log('----current station:', this.currentStation);

    });
    return this.currentStation;
    // this.currentStation = this.stationService.getLocationStations().filter((station) => {
    //   return station.stationPath === route.params['station'];
    //
    // })[0];

  }

}

用于检索和存储与组件相关的信息的独立服务

车站服务台

import { Injectable } from '@angular/core';
import {HttpClient, HttpParams} from '@angular/common/http';
import {AuthService} from './auth.service';
import {Params} from '@angular/router';
@Injectable({
  providedIn: 'root'
})


export class ApisService {

  GET_BATCH_SCHEDULE = 'http://localhost:8000/getbatchplan';
  GET_USER_STATIONS = 'http://localhost:7071/api/getUserStations';
  GET_USER_LOCATIONS = 'http://localhost:7071/api/getUserLocations';




  constructor(private httpClient: HttpClient, private authService: AuthService) { }


  getCutplanBatches() {
    return this.httpClient.get(this.GET_BATCH_SCHEDULE);
  }


  getStations(location: string) {
    if (location === undefined){
      console.log("undefined location call");
      location = 'aqua';
    }
    const params = new HttpParams()
      .set('email', this.authService.getAuthenticateduserInfo().displayableId)
      .append('location', location);

    return this.httpClient.get(this.GET_USER_STATIONS, { params: params });

  }

  getLocations() {
    const params = new HttpParams()
      .set('email', this.authService.getAuthenticateduserInfo().displayableId);

    return this.httpClient.get(this.GET_USER_LOCATIONS, { params: params });

  }


}

import {Injectable} from '@angular/core';
import {ApisService} from './apis.service';
import {StationModel} from '../models/station.model';
import {BehaviorSubject, Observable} from 'rxjs';


@Injectable({
  providedIn: 'root'
})


export class StationService {
  userStations: BehaviorSubject<StationModel[]>;
  userLocation: string;

  constructor(private apiService: ApisService) {
    this.userStations = new BehaviorSubject<StationModel[]>([]);
    this.setLocationStations('aqua');

  }
  setLocation(location: string) {
    this.userLocation = location;

  }
  getLocation() {

      return this.userLocation;


  }
  setLocationStations(locationSelect: string) {
    this.apiService.getStations(locationSelect).subscribe((data: StationModel[]) => {
      this.userStations.next(data['stations']);
      console.log('setting user locations:', this.userStations);
      return this.userStations;

    });


  }
  public getLocationStations(): Observable<StationModel[]> {
    console.log('inside station service:', this.userStations);
    console.log('inside station service loc:', this.userLocation);


    return this.userStations.asObservable();

  }

}

import {ActivatedRouteSnapshot, Resolve, RouterStateSnapshot} from '@angular/router';
import {Observable} from 'rxjs';
import {StationService} from '../../services/station.service';
import {Injectable} from '@angular/core';
import {StationModel} from '../../models/station.model';
@Injectable({
  providedIn: 'root'
})
export class StationRouteResolver implements Resolve<StationModel> {
  currentStation: StationModel;
  constructor(private stationService: StationService) {}

  resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
    console.log('Resolves:', route.params['location']);

    if (this.stationService.getLocation() === undefined) {
      console.log('Initial setting:', route.params['location']);
      this.stationService.setLocation(route.params['location']);

    }else if (this.stationService.getLocation() !== route.params['location']) {
      console.log('Changing location settings:', route.params['location']);
      this.stationService.setLocation(route.params['location']);
    }else{
      console.log('Same location found!');
    }

    this.stationService.getLocationStations().subscribe((stations: StationModel[]) => {
      console.log('observer resolver:', stations);

      this.currentStation = stations.filter((station) => {
        return station.stationPath === route.params['station'];

      })[0];
      console.log('----current station:', this.currentStation);

    });
    return this.currentStation;
    // this.currentStation = this.stationService.getLocationStations().filter((station) => {
    //   return station.stationPath === route.params['station'];
    //
    // })[0];

  }

}

使用模板中的*ngIf选择正确的组件

station.component.html

<app-batch-list-view *ngIf="station.stationType == 'o'"></app-batch-list-view>
<app-dashboard-view *ngIf="station.stationType == 'm'"></app-dashboard-view>
<app-print-view *ngIf="station.stationType == 'p'"></app-print-view>

问题是在启动和刷新页面时，特别是在station.component中，我得到一个变量未定义错误，因为 station.stationType未定义，应用程序从此中断

但是，如果我返回并返回到同一路线，这是可行的（使用ngif加载组件时没有任何错误）

我想知道这是因为使用了解析器还是我的实现中出现了错误

---

如果我的问题不太清楚，很抱歉。如果有人能指出问题所在，那将非常有帮助。

试试这个：这是因为没有定义可为null的变量站或不同步调用api

对于第一个：

站：可为空

或

对于第二个：您可以在
station.component.ts
中使用
ngAfterViewInit（）
而不是
ngOnInit
尝试将这些
station.stationType
更改为组件模板中的此
station？.stationType
。哇，这就解决了！但根本原因可能是什么？是因为异步方法吗？是因为异步方法吗，是的。这是一个普遍的问题。