HttpClient post返回true，但組件訂閱function為false

Question

我正在嘗試從按鈕登錄。 我有帶有雙向綁定的模板輸入字段來設置用戶名和密碼的字符串值。 通過事件綁定，登錄按鈕觸發 login() 方法。 此登錄方法創建一個本地憑據 object，它吸收了用戶名和密碼。 憑證 object 被傳遞給 HttpClient 服務方法。 服務方法命中后端端點，並傳回 boolean，指示憑據是否在數據庫中。

在組件 class 中，訂閱了服務方法，並且 - 正如我解釋的那樣 - 在訂閱期間， loginSuccess boolean 被分配了服務方法返回的值。 除了......我對此的理解一定是錯誤的，因為這並沒有按照我期望的順序發生。

登錄組件.ts

export class LoginComponent implements OnInit, OnDestroy {
  // credential: Credential;
  username: string;
  password: string;
  user: User;
  loginMessage: string = "";
  loginSuccess: boolean = false;
  userSubscription: Subscription;

  constructor(private userService: UserService) { }

  ngOnInit(): void {
  }
  ngOnDestroy(): void {
    // this.userSubscription.unsubscribe();
  }

  login(): void {
    if(this.username != null){
      var credential: Credential = { username: this.username, password: this.password };
      
      this.userService.authenticateCredential(credential).subscribe(subscribeCheck => { 
        this.loginSuccess = subscribeCheck;
        console.log("mark 04: loginSuccess = " + this.loginSuccess);
      });
      console.log("mark 13: loginSuccess = " + this.loginSuccess);
    }
    console.log("mark 14: loginSuccess = " + this.loginSuccess);

    if(this.loginSuccess){
      console.log("mark 24");
      this.userService.getUser(credential).subscribe(subscriptionUser => {
        this.user = subscriptionUser;
      });
        this.loginMessage = "";
    } else {
      console.log("mark 25");
      this.loginMessage = "LOGIN FAILURE!!!";
    }
  }
}

控制台顯示，因為執行順序不是我期望的，所以登錄失敗。 boolean 變量 loginSuccess 在遇到 if() 條件時始終為 false，因為 if() 條件始終在 loginSuccess 由 HttpClient observable 分配之前執行。 為什么會這樣？ 我該如何解決？

Answer 1

您對if(this.loginSuccess){的檢查應該在訂閱中。 你是對的，這里的順序很重要。

export class LoginComponent implements OnInit, OnDestroy {
      // credential: Credential;
      username: string;
      password: string;
      user: User;
      loginMessage: string = "";
      loginSuccess: boolean = false;
      userSubscription: Subscription;
    
      constructor(private userService: UserService) { }
    
      ngOnInit(): void {
      }
      ngOnDestroy(): void {
        // this.userSubscription.unsubscribe();
      }
    
      login(): void {
        if(this.username != null){
          var credential: Credential = { username: this.username, password: this.password };
          
          this.userService.authenticateCredential(credential).subscribe(subscribeCheck => { 
            this.loginSuccess = subscribeCheck;
            if(this.loginSuccess){
               console.log("mark 24");
               this.userService.getUser(credential).subscribe(subscriptionUser => {
                  this.user = subscriptionUser;
               });
              this.loginMessage = "";
            } else {
               console.log("mark 25");
               this.loginMessage = "LOGIN FAILURE!!!";
            }
            console.log("mark 04: loginSuccess = " + this.loginSuccess);
          });
          console.log("mark 13: loginSuccess = " + this.loginSuccess);
        }
        console.log("mark 14: loginSuccess = " + this.loginSuccess);
    
        
      }
    }