Angular / Typescript / Firestore - 如何在 if 语句中返回可观察值

Question

我正在使用 Angular 和 Firestore。我正在检查 firestore 以获取我的路由守卫内的值。

我发现在页面刷新时，它返回为未定义。但是，如果我只是硬编码返回 true 或 false，它就可以工作。

我的 if 语句中的任何日志总是正确返回，但由于某种原因似乎没有更新我的全局变量。

如果我使用我的站点导航返回到根目录并浏览我的站点，它可以正常工作。但是，当我刷新页面时，它返回为未定义。

这可能是范围界定问题吗？

路线守卫

import { Injectable } from '@angular/core';
import { ActivatedRouteSnapshot, RouterStateSnapshot, CanActivate, Router } from '@angular/router';
import { AuthService } from './auth.service';

import { AngularFirestore, AngularFirestoreCollection, AngularFirestoreDocument } from 'angularfire2/firestore';
import { Subscription } from 'rxjs/Subscription';


//testing
import { Observable } from 'rxjs/Observable';
import { AngularFireAuth } from 'angularfire2/auth';

@Injectable()
export class CheckBillingService implements CanActivate {
    private _subscription: Subscription;
    private userBillingDocRef: AngularFirestoreDocument<any>;
    userBilling: Observable<any>;
    public activeAccount:Observable<boolean>

    constructor(private authService: AuthService,
                private router: Router,
                private auth: AngularFireAuth,
                private readonly afs: AngularFirestore) {}

    canActivate(): Observable<boolean> {
        this.authService.user.subscribe((user) => {
            if (user) {
                var userId = user.uid;

                this.userBillingDocRef = this.afs.doc('user_billing/${userId}');

                this.userBilling = this.userBillingDocRef.snapshotChanges();
                this.userBilling.subscribe((value) => {

                    const data = value.payload.data();

                    if (data.account_status == "Active") {
                        this.activeAccount = Observable.of(true);
                        console.log('inside if statement for active = ', this.activeAccount);
                    } else {
                        this.activeAccount = Observable.of(false);
                        console.log('inside if statement for not active = ', this.activeAccount);
                        this.router.navigate(['resubscribe']);
                        return Observable.of(false);
                    }

                    console.log('userBilling.subscribe = ', this.activeAccount);
                });

                console.log('just outside userBilling.subscribe = ', this.activeAccount);
            }
        });

        // When refreshig my page, this returns as undefined.
        // If I navigate to the correct page and work my way through the site it works fine
        // However, refresh returns undefined.

        console.log('out of auth = ', this.activeAccount);

        return this.activeAccount;
    }
}

Answer 1

Observables 可以是异步的；它们通常用于此目的。在这种情况下，订阅之外的代码会在内部订阅之前执行。

这就是为什么它看起来像是“不更新”变量的原因。是的，但是您没有在正确的时间访问它们。当您对值进行硬编码时它会起作用，因为订阅是同步执行的。

Answer 2

根据您的代码，页面将在您的可观察方法返回之前运行，因为它是异步运行的，而不是像这样返回完整的可观察方法

 canActivate(): Observable<boolean> {

    return Observable.create(observer=> {
this.authService.user.subscribe((user) => {

                if (user) {

                    var userId = user.uid;

                    this.userBillingDocRef = this.afs.doc('user_billing/${userId}');

                    this.userBilling = this.userBillingDocRef.snapshotChanges();
                    this.userBilling.subscribe((value) => {

                        const data = value.payload.data();

                        if (data.account_status == "Active") {
                            this.activeAccount = Observable.of(true);
 // observe here 
        observer.next(true)
                            console.log('inside if statement for active = ', this.activeAccount);
                        } else {
                            this.activeAccount = Observable.of(false);
          // observe here 
        observer.next(false)
                            console.log('inside if statement for not active = ', this.activeAccount);
                            this.router.navigate(['resubscribe']);
                        }

                        console.log('userBilling.subscribe = ', this.activeAccount);
                    });

                    console.log('just outside userBilling.subscribe = ', this.activeAccount);

                }

            });
    });


            // When refreshig my page, this returns as undefined.
            // If I navigate to the correct page and work my way through the site it works fine
            // However, refresh returns undefined.

            console.log('out of auth = ', this.activeAccount);

        }

注意我在Observer.create 中包装了所有内容的位置，您可以在此处了解更多信息https://stackoverflow.com/a/44334611/5836034

然后observer.next 将返回您真正希望canActivate 挂钩做出反应的内容

  // observe here 
        observer.next(true)
    observer.next(false)