Angular 6 Service: Cannot get value which should be set in Constructor

Question

I have one service, one component and one resolver as following. There are some codes in Service Constructor, it should set value in Service, then when I link to certain path, the Resolver of this route would call certain Service Method, and the Method should be able to read the value which already set by Constructor.

Service:

@Injectable({
  providedIn: 'root'
})
export class BuildjsonService {

  public currentUser: User;

  constructor() {
    console.log('BuildjsonService constructor');
    this.currentUser = JSON.parse(sessionStorage.getItem('currentUser'));
   }


  genReqContent(fmCode: string, caseKey: string, transKey: string, content: string){
    
    let reqContent : ReqContent = new ReqContent();
    
    console.log('genReqContent=' + JSON.stringify(this.currentUser));
    
    reqContent.bankerId = this.currentUser.loginID;

    return reqContent;

  }

Click on certain route, rosolver fired:

@Injectable()
export class GetSubDeptResolver implements Resolve<any> {

  constructor(private httpClient: HttpClient,
              private buildJsonSrv: BuildjsonService){}

  resolve(): Observable<any> {

    <!-- calling service-->
    let reqCont = this.buildJsonSrv.genReqContent('', '', '', content);

    let reqJsonObj: ReqJsonObj = this.buildJsonSrv.genJsonReq(reqCont, new FlowContent(), new TxnInfoContent());
    return this.httpClient.post<any>('http://localhost:2387/utility/GetSubDept', reqJsonObj)

  }

}

However, when Resolver calling genReqContent() in Service, 'this.currentUser' is null.

I can see that this Service is loaded and constructor is called when App starts, so the currentUser should already has value, however it's gone when being used later.

Am I doing something wrong? Thank you.

Just wondering: You are not opening that link in a new tab or window, are you? — Erbsenkoenig
– Erbsenkoenig, Commented Jul 9, 2019 at 7:46
@Erbsenkoenig Thank you for reply. No, it's one the same tab. — dmd
– dmd, Commented Jul 9, 2019 at 7:59

Knelis · Accepted Answer · 2019-07-09 08:08:06Z

2

It appears that sessionStorage does not contain a value for currentUser at the time your service is instantiated. You could change currentUser to a getter, which only calls the storage when it's actually needed. This would also give you the latest instance of currentUser, in case its value changes (e.g. as a result of token renewal by another service).

@Injectable({
  providedIn: 'root'
})
export class BuildjsonService {

  get currentUser() {
    const user = sessionStorage.getItem('currentUser');

    if (user === null) {
      throw new Error('No user found in sessionStorage.');
    }

    return JSON.parse(user) as User;
  }

  constructor() {
    console.log('BuildjsonService constructor');
  }
}

edited Jul 9, 2019 at 8:08

answered Jul 9, 2019 at 7:57

Knelis

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1 Comment

dmd Over a year ago

Thank you! After checking log one more time, this service indeed is instantiated before currentUser being add to the sessionStorage. Getter is great, thank you!

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