Promise.all 无法按预期使用数组

Question

这是我的代码，我从一个空数组开始，想调用一个服务来对填充的数组进行一些处理。我使用两次调用服务来填充数组，这些服务调用 API 来接收要插入到数组中的元素。

我正在尝试使用承诺来确保我的数组 subscribers 充满了正确的订阅者对象，但是方法 processSubscribers 总是收到一个空数组，即使对象最终确实被添加到订阅者数组中（如 chrome 调试所示）。

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

这行代码的结果是订阅而不是承诺

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

这意味着您的 promise 数组不包含承诺，这就是 promise.all 不起作用的原因

你可以做到

promises.push(this.serviceB.getSubscriber(sub.subscriberId).toPromise())

或

promises.push(this.serviceB.getSubscriber(sub.subscriberId).toPromise().then(x => ... ))

Promise.all 无法按预期使用数组

Promise.all not working as expected with array

typescript

es6-promise

angular