没有 first on Api 方法，forkJoin 无法工作

Question

我已经写了forkJoin，如图所示，如果我不将api方法设置为first，below.It不起作用（也没有错误）。你能告诉我为什么？

my.ts

    let getMyBookMarksApi = this.userService.getMyBookMarks(this.page);//needs first()
    let getMyTopicsApi = this.userService.myTopic();//needs first()

    Observable.forkJoin([getMyBookMarksApi, getMyTopicsApi])
        .subscribe(res => {
            this.setMyProfile(res[0]);
            this.arrangeMyTopics(res[1]);
        },
        error => { },
        () => { });

service.ts

 myTopic() {
 return this.api.get(config.myTopics).map((res: any) => res.json()).first();//without first forkjoin is not working.Why?
 }

api.ts

 get(api) {
        return new Observable(observer => {
            let header = new Headers();
            this.createHeader(header)
                .then(() => {
                    let options = new BaseRequestOptions();
                    options.withCredentials = true;
                    options.headers = header;
                    this.http.get(api, options)
                        .subscribe(response => {
                            observer.next(response);
                        }, (e) => {
                            observer.error(e);
                        });
                })
        })
    }

Api 响应是这样的：

{
  "num_of_definitions": 11,
  "categories": [
    {
      "id": 68,
      "name": "Founders",
      "num_of_definitions": 1,
      "icon": {
        "large": ""
      },
      "from_color": "#1E3C72",
      "to_color": "#2A5298"
    },
    {
      "id": 27,
      "name": "Innovation",
      "num_of_definitions": 1,
      "icon": {
        "large": ""
      },
      "from_color": "#EE0979",
      "to_color": "#FF6A00"
    },
    {
      "id": 58,
      "name": "Life success",
      "num_of_definitions": 1,
      "icon": {
        "large": ""
      },
      "from_color": "#D53369",
      "to_color": "#CBAD6D"
    },

  ]
}

Answer 1

Forkjoin 的工作原理是并行订阅所有可观察对象，并且只有当它们全部完成后才会重新加入。这里的关键字是他们完成的时间。运算符 .first() 从可观察对象中获取第一个发出的元素，然后完成。可能是因为您的源 observables 没有完成

为了完成示例，在 onNext

之后添加 onComplete 行

 get(api) {
    return new Observable(observer => {
        let header = new Headers();
        this.createHeader(header)
            .then(() => {
                let options = new BaseRequestOptions();
                options.withCredentials = true;
                options.headers = header;
                this.http.get(api, options)
                    .subscribe(response => {
                        observer.next(response);
                        // add this line, it should trigger the completion of the outer observable
                        observer.complete();
                    }, (e) => {
                        observer.error(e);
                    });
            })
    })
}

没有 first on Api 方法，forkJoin 无法工作

forkJoin is not working without first on Api method

angular

typescript

observable

fork-join