Angular2:switchMap不会取消以前的http调用 [英] Angular2: switchMap not canceling previous http calls

问题描述

我正在尝试使用switchMap取消Angular2中的所有先前的http调用. 代码基本上是

I am trying to use switchMap to cancel any previous http calls in Angular2. The code is basically

var run = ():Observable<any> => {
        var url = 'http://...'
        return this._http.get(url)
            .map(result => {
                return var xmlData:string = result.text()

            });
    }


    function pollTasks() {
        return Observable.of(1)
            .switchMap(() => run())
            .map(res => res)
    }

    // caller can do subscription and store it as a handle:
    let tasksSubscription =
        pollTasks()
            .subscribe(data => {
                console.log('aa'+data)
            });

，所以我连续多次调用整个源，并收到了一些答复(即:aa + data)

and so I call the entire source several times in a row and receive several replies (i.e.: aa+data)

我当时印象中switchMap应该取消先前的呼叫.

I was under the impression switchMap should cancel the previous calls.

推荐答案

请求需要源自同一基础流.这是一个工厂函数，它将创建一个http服务实例，该实例应该执行您想要的操作:

The requests need to originate from the same underlying stream. Here's a factory function that will create an http service instance that should do what you want:

function httpService(url) {
   // httpRequest$ stream that allows us to push new requests
   const httpRequest$ = new Rx.Subject();

   // httpResponse$ stream that allows clients of the httpService
   // to handle our responses (fetch here can be replaced with whatever
   // http library you're using).
   const httpResponse$ = httpRequest$
       .switchMap(() => fetch(url));


   // Expose a single method get() that pushes a new
   // request onto the httpRequest stream. Expose the
   // httpResponse$ stream to handle responses.
   return {
       get: () => httpRequest$.next(),
       httpResponse$
   };
}

现在，客户端代码可以像这样使用此服务:

And now the client code can use this service like this:

const http = httpService('http://my.api.com/resource');

// Subscribe to any responses
http.httpResponse$.subscribe(resp => console.log(resp));

// Call http.get() a bunch of times: should only get one log!!
http.get();
http.get();
http.get();

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