订阅承诺 [英] Subscription to promise

问题描述

在我的 Angular 7 应用程序中，我有下一个功能:

In my Angular 7 application I have next function:

  getUserData(uid) {
    return this.fireStore.collection('users').doc(uid).valueChanges().subscribe(data => {
      this.writeCookie(data)
      this.currentUser = data;
    })
  }

我想在另一个方法中使用这个函数:

And I want to use this function inside another method:

   someMethod() {
      ...
      new Promise(this.getUserData(uid))
         .then(() => {...})
      ...
   }

但我不能这样做，因为 TypeScript 会抛出错误:

But I can't do this, because TypeScript throw an error:

订阅"类型的参数不可分配给类型参数'(resolve: (value?: {} | PromiseLike<{}>) => void, reject: (reason?:任何) => 无效) => 无效'.类型订阅"不匹配签名 '(resolve: (value?: {} | PromiseLike<{}>) => void,拒绝:(原因?:任何)=> void):void'.ts(2345)

Argument of type 'Subscription' is not assignable to parameter of type '(resolve: (value?: {} | PromiseLike<{}>) => void, reject: (reason?: any) => void) => void'. Type 'Subscription' provides no match for the signature '(resolve: (value?: {} | PromiseLike<{}>) => void, reject: (reason?: any) => void): void'.ts(2345)

如何将 getUserData() 方法转换为 promise，或使用 forJoin 代替?

How can I transform getUserData() method to a promise, or use forJoin instead?

提前致谢.

推荐答案

subscribe 将类型从 Observable 更改为 Subscription，从而导致类型错误.

subscribe changes the type from Observable to Subscription, thus causing the type error.

您可能想要的是将 Observable 转换为 Promise，同时保留函数调用.你可以通过 tap 管道传输 Observable，然后用 toPromise 转换结果.像这样:

What you probably want is to convert your Observable to a Promise, while preserving the function call. You can do this, by piping the Observable through tap and then converting the result with toPromise. Like this:

getUserData(uid) {
  return this.fireStore.collection('users').doc(uid).valueChanges().pipe(
    tap(data => {
      this.writeCookie(data)
      this.currentUser = data;
    }),
    first()
  ).toPromise()
}

确保创建一个完整的管道，就像您可以使用 first 运算符所做的那样，否则 Promise 将永远无法解析.

Make sure to create a completing pipe, like you can do with the first operator, otherwise the Promise will never resolve.

您可以在消费者中省略 new Promise(...).

You can leave out new Promise(...) in your consumer.

这篇关于订阅承诺的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！