Angular2可观察和无极

本文介绍了Angular2可观察和无极的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我开始使用Angular2 Observable，但是找不到与Promises一起使用的.then类似的东西.

I started using Angular2 Observable, but I can't find something similar to .then that I used with Promises.

这就是我要完成的事情.

This is what I want to accomplish.

public login() { this._user = AuthService.getInstance().login(this._loginInfo); }

来自auth.service.ts的代码

return this._httpClient.post('LoginAction', credentials) .map(res => res.json()) .subscribe(user => { return new User(user); });

带有承诺，login函数将返回Promise，最终将转换为服务器的实际响应.但是使用Observable，这将无法正常工作.

With promises, login function would return Promise, that would eventually transform to actual response from server. But with Observable this won't work.

有没有办法做类似的事情?我想避免需要将订阅放入component的login函数中.我希望能够完成服务中的所有工作，并将实际对象返回给component.

Is there a way to do similar thing? I want to avoid need of putting subscribe inside component's login function. I want to be able to do all the work in service, and to return actual object to component.

此外，我尝试使用toPromise创建Promise，但是我一直在获取toPromise is not a function.

Also, I tried to create Promise, with toPromise, but I keep getting toPromise is not a function.

p.s. _httpClient是我对angular2 http的包装，在其中我通过添加一些标头等来准备请求.

p.s. _httpClient is my wrapper around angular2 http in which I prepare request by adding some headers etc.

return this._httpClient.post('LoginAction', credentials) .map(res => res.json()) .toPromise(). <-- i keep getting that it is not a function then(user => { return new User(user); });

这样做，我的组件将获得对象(这是它所需要的)，并且在服务中，我可以做其他事情(例如，一旦我登录他，将用户保存到本地存储中).

by doing this, my component will get object (which is what it need), and in service i could do additional things (like saving user to localstorage, once I logged him).

然后我切换到了Promise，因为对Observable进行的操作不起作用(或者我做错了)吗?

And I switched to Promise, because doing same with Observable is not working (or I am doing it wrong)?

我看到返回的对象是可观察的(在调用Promise之前)，但是我确实没有看到toPromise函数.

I see that returned object is Observable (before calling toPromise), but I don't see toPromise function indeed.

推荐答案

当您呼叫subscribe(...)时，将返回一个没有toPromise()的Subscription.如果将代码从subscribe移到map，则可以使用toPromise()代替subscribe

When you call subscribe(...) a Subscription is returned which doesn't have a toPromise(). If you move the code from subscribe to map you can use toPromise() instead of subscribe

return this._httpClient.post('LoginAction', credentials) .map(res => res.json()) .map(user => { return new User(user); }).toPromise();

，呼叫者将得到一个Promise，他可以在其中使用

and the caller will get a Promise where he can get the value using

public login() { this._user = AuthService.getInstance().login(this._loginInfo) .then(result => { doSomething(); }); }

，但是如果省略`.toPromise()，并且调用方像

but you get the same result if you omit `.toPromise() and the caller uses it like

public login() { this._user = AuthService.getInstance().login(this._loginInfo) .subscribe(result => { doSomething(); }); }

唯一的区别是subscribe()而不是then()，并且如果库的用户更喜欢反应式样式，他将更喜欢像以前一样使用subscribe().

where the only difference is subscribe() instead of then() and if the user of the library prefers the reactive style he will prefer using subscribe() like he is used to.