带有角度 HttpClient 的 RxJs switchMap [英] RxJs switchMap with angular HttpClient

问题描述

每当触发新请求时，我都有一个用例，任何已经在进行中的 http 请求都应该被取消/忽略.

I have a use case whenever a new request is triggered, any http requests that are already in flight should be cancelled / ignored.

例如:

• 一个请求(比如 #2)传入，而请求 #1 响应时间太长/网络连接速度慢.
• 在这种情况下，#2 从服务器获得非常快的响应，然后在任何时候，即使 #1 带着响应返回 HTTP 响应observable 应该被忽略.
• 我面临的问题是，首先组件显示来自请求 #2 的响应值，并在请求 #1 完成时再次更新(这不应该发生).

我认为 switchMap 取消了 obervables/维护了发出 observable 值的顺序.

I figured that switchMap cancels obervables / maintains the order in which the observable values are emitted.

摘自我的 service.ts

Obervable.of('myServiceUrl')
             .switchMap(url => this.httpRequest(url) )
              .subscribe( response => {
                   // implementation
                   /** Update an observable with the 
                       with latest changes from response. this will be 
                       displayed in a component as async */
                });


private httpRequest(url) {
        return this.httpClient.get('myUrl', { observe: 'response' });
}

上述实现不起作用.有人能找出这个用例的正确实现吗?

The above implementation doesn't work. Could some one figure out the correct implementation for this usecase.

推荐答案

我有以下代码摘录，switchMap 实现成功.

I have the below code excerpt with which the switchMap implementation was successfull.

class MyClass {
    private domain: string;
    private myServiceUri: subject;
    myData$: Observable<any>;

        constructor(private http: HttpClient) {
            .....
            this.myServiceUri = new Subject();
            this.myServiceUri.switchMap(uri => {
                    return this.http.get(uri , { observe: 'response' })
                            // we have to catch the error else the observable sequence will complete
                            .catch(error => {
                                // handle error scenario
                                return Obervable.empty(); //need this to continue the stream
                            });
                    })
                    .subscribe(response => {
                        this.myData$.next(response);
                    });
        }

        getData(uri: string) {
            this.myServiceUri.next(this.domain + uri); // this will trigger the request     
        }

    }

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