以角度保留http调用的顺序

Question

我正在努力解决我面临的订单问题，我在SO上找到的几种方法都没有成功。

我有一个方法，我正在为leaflet图层数组加载一些数据：

private loadSelectedTileLayersCapabilities(): void {

        let tempTileLayer;

        this.selectedTileLayerIds.forEach(
            (selectedTileLayer: string) => {
                tempTileLayer = this.getTileLayerById(selectedTileLayer);

                this.capabilitiesService.getTileLayerDimensions(tempTileLayer.url, tempTileLayer.name, tempTileLayer.id)
                .subscribe(
                    dimensions => this.displayNewTileLayer(dimensions)
                );
            }
        );
    }

然后我有一个方法，http调用正在发生：

public getTileLayerDimensions(urlToFormat: string, tileLayerName: string, tileLayerId: string): Observable<Dimensions> {

        const capabilitiesUrl = `serviceUrl`;

        return this.httpClient.get(capabilitiesUrl, {responseType: "text"})
            .map(res => {

                // Doing stuff with data

                return dataForLayer;
            });

    }

问题是，displayNewTileLayer(dimensions)方法是以随机顺序调用的。有没有办法保存selectedTileLayerIds数组中存储项目的顺序？

Answer 1

由于http调用是异步的，因此响应可能不会以请求的相同顺序到达。你可以做的是创建一个请求列表，创建一个forkJoin并等待所有响应解决。然后，您可以为所有响应调用displayNewTileLayer(dimensions)方法。

这是一个例子

    const httpCalls = []; // store the requests here
    for (let i = 0; i < 3; i++) {
      httpCalls.push(this.http.get('someUrl').map(response => response));
    }
    forkJoin(httpCalls).subscribe(res => {
      // all responses completed. returns an array of data (one for each response).
      console.log('res', res);
    });

在您的情况下，此代码可能有效:(代码未经过测试，您可能必须在代码中导入forkJoin运算符）

import { forkJoin } from 'rxjs/observable/forkJoin';

private loadSelectedTileLayersCapabilities(): void {

    let tempTileLayer;
    let requests = []:

    this.selectedTileLayerIds.forEach(
        (selectedTileLayer: string) => {
            tempTileLayer = this.getTileLayerById(selectedTileLayer);
            const request = this.capabilitiesService.getTileLayerDimensions(tempTileLayer.url, tempTileLayer.name, tempTileLayer.id)
            requests.push(request);

        }
    );
    forkJoin(requests).subscribe(res => {
      res.forEach(dimension => this.displayNewTileLayer(dimension));
    })
}

Answer 2

我会考虑使用concat运算符。

您的代码如下所示

    private loadSelectedTileLayersCapabilities(): void {

            let tempTileLayer;
            let concatObs;

            this.selectedTileLayerIds.forEach(
                (selectedTileLayer: string) => {
                    tempTileLayer = this.getTileLayerById(selectedTileLayer);

                    const httpCall = this.capabilitiesService.getTileLayerDimensions(tempTileLayer.url, tempTileLayer.name, tempTileLayer.id);
                    if (!concatObs) {
                        concatObs = httpCall);
                     } else {
                         concatObs.concat(httpCall);
                     }

                }
            );
            concatObs.subscribe(
                dimensions => this.displayNewTileLayer(dimensions)
            );
        }

这样，concatObs以与数组selectedTileLayersIds相同的顺序发出。您应该考虑是否可以将排序逻辑移动到服务器，即具有接收id数组（selectedTileLayersIds）并返回维度数组的服务。通过这种方式，您可以减少网络流量并避免连续的同步http调用。