angular - 在以 Angular 调用之前等待数组完成填充

Question

这是我的代码，我从一个空数组开始，想要调用一个对填充数组进行一些操作的服务。我使用两次对服务的调用来填充数组，这些服务调用 API 来接收要插入到数组中的元素。

我不知道如何让最后一个服务调用等到数组被填充后再执行。我认为我有两个单独的服务调用需要等待，而且它们都有 forEach 循环，这使得这比原本可能的更困难。有任何想法吗？

const subscribers: ISubscriber[] = [];

this.selectedChildren.forEach(child => {
    this.serviceA.getSubscribers(child.id).subscribe( (subs: ISubscriber[]) => {
        subs.forEach(s => {
            subscribers.push(s);
        });
    });
});

this.selectedSubscribers.forEach(sub => {
    this.serviceB.getSubscriber(sub.subscriberId).subscribe( (sub: ISubscriber) => {
        subscribers.push(sub);
    });
});

// subscribers is always empty when this call is made 
// since above code hasn't finished executing
this.serviceC.processSubscribers(subscribers).subscribe( sub => {
    this.toastr.success('Success!');
});

异步/等待尝试不起作用:

async doSomething(){
    const subscribers: ISubscriber[] = [];

    await this.selectedChildren.forEach(async child => {
        await this.serviceA.getSubscribers(child.id).subscribe( (subs: ISubscriber[]) => {
            subs.forEach(s => {
                subscribers.push(s);
            });
        });
    });

    await this.selectedSubscribers.forEach(async sub => {
        await this.serviceB.getSubscriber(sub.subscriberId).subscribe( (sub: ISubscriber) => {
            subscribers.push(sub);
        });
    });

    // subscribers is always empty when this call is made 
    // since above code hasn't finished executing
    this.serviceC.processSubscribers(this.id, subscribers).subscribe( id => {
        this.toastr.success('Success!');
    });
}

Promise.all 尝试不起作用:

doSomething(){
    const subscribers: ISubscriber[] = [];
    const promises = [];

    this.selectedChildren.forEach(child => {
        promises.push(this.serviceA.getSubscribers(child.id).subscribe( (subs: ISubscriber[]) => {
            subs.forEach(s => {
                subscribers.push(s);
            });
        }));
    });

    this.selectedSubscribers.forEach(sub => {
        promises.push(this.serviceB.getSubscriber(sub.subscriberId).subscribe( (sub: ISubscriber) => {
            subscribers.push(sub);
        }));
    });

    // subscribers is always empty when this call is made 
    // since above code hasn't finished executing
    Promise.all(promises).then( a => {
        this.serviceC.processSubscribers(this.id, subscribers).subscribe( id => {
            this.toastr.success('Success!');
        });
    });
}

Answer 1

使用 rxjs 运算符的解决方案:

• 请记住，您在可观察链中应该只有1 个订阅
• combineLatest 相当于 Promise.all
• switchmap允许您将serviceA和serviceB的结果类型更改为serviceC

    const subscribers: ISubscriber[] = [];
    const subscriberObservables = [];

    // First you add all async calls into an array
    this.selectedChildren.forEach(child => {
        subscriberObservables.push(this.serviceA.getSubscribers(child.id));
    });

    this.selectedSubscribers.forEach(sub => {
        subscriberObservables.push(this.serviceB.getSubscriber(sub.subscriberId));
    });

    // then you run all of them in parallel
    combineLatest(subscriberObservables)
      .pipe(
        map((arrayOfArrays:ISubscriber[][]) => arrayOfArrays.flat()),
        switchMap( (subs: ISubscriber[]) => this.serviceC.processSubscribers(subscribers))
      )
      .subscribe( sub => {
          this.toastr.success('Success!');
      });