订阅后的Angular 2数组具有元素，但长度为0 [英] Angular 2 array after subscribe has elements but length is 0

问题描述

我正在使用Angular 2，并且发现了意外的行为.

I'm using Angular 2 and I have noticed an unexpected behaviour.

我有一个数据源类，该类扩展了DataSource，具有两个变量:

I have a datasource class, which extends DataSource, with two variables:

private archives = new BehaviorSubject<MyArchive[]>([]);
public archives$: Observable<MyArchive[]> = this.archives.asObservable();
private filteredArchive: MyArchive[];

我在课堂上以这种方式更新档案:

I update archives this way within the class:

this.archives.next(this.filteredArchive);

在另一个类的外部，我尝试订阅可观察的对象，但是它不起作用:

Outside in another class I try to subscribe to the observable but it doesn't work:

ngAfterViewInit(): void {

    this.dataSource.archives$.subscribe((archive: Array<MyArchive>) => {

        console.log(archive.length);
        console.log(archive);
        console.log(archive.length);
    }
}

在控制台日志中它打印:

In the console log it prints:

0
<THE ARCHIVE WITH AN OBJECT INSIDE AS IT SHOULD BE, WITH LENGTH = 1>
0

因为长度为0，所以我无法迭代归档变量.这是怎么回事?

So that I can't iterate on the archive variable because its length is 0. What's going on here?

推荐答案

我解决了这个问题. 我忘记了this.filteredArchive是由HTTP GET请求更新的.我试图使用forEach在this.filteredArchive中推送数据，但是当接收到所有数据时，我忘记了调用then(). 因此，我试图使用订阅访问尚未准备好的结果.

I solved the problem. I forgot that this.filteredArchive is updated by an HTTP GET request. I was trying to push data within this.filteredArchive using forEach, but I forgot to call then() when all the data are received. Hence I was trying to access, using subscribe, a result that was not yet ready.

感谢大家的答复！

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