Angular 2-在调用方法之前消耗其他服务的服务 [英] Angular 2 - Services consuming others services before call a method

问题描述

我有这种情况.

backend.json

backend.json

{
"devServer": "http://server1/'",
"proServer" : "http://server2/'",
"use" :  "devServer"
}

global.service.ts

global.service.ts

import {Injectable} from '@angular/core';
import {Http, HTTP_PROVIDERS, Response, RequestOptions, URLSearchParams} from '@angular/http';
@Injectable()
export class GlobalService {
constructor(private _http: Http){}
getBackendServer(){
    return this.server = this._http.get('./backend.json')
        .map((res:Response) => res.json())
}
}

我还有其他服务:search.service.ts

And I've this other service: search.service.ts

import {Injectable} from '@angular/core';
import {Http, HTTP_PROVIDERS, Response, RequestOptions, URLSearchParams} from '@angular/http';
import {GlobalService} from '../services/global.service';
import 'rxjs/add/operator/map';
@Injectable()
export class SearchService {
server;
constructor( private _http: Http, private gs: GlobalService ) {
    this.server = gs.getBackendServer().subscribe(
        (data) => {
            this.server = data[data.use];
        },
        (err) => {
            console.log(err);  
        }
    );
}
DoGeneralSearch(params:Search){
    console.log(this.server);
    let options = this.buildOptions(params);
    return this._http.get(this.server + 'room/search', options)
     .map((res:Response) => res.json())
} 
}

我想做的事情:看起来很明显:我想将有关后端服务器URL的信息保存在JSON文件中-全局服务应返回服务器，以便可以在搜索服务的任何方法中使用

What I want to do: Looks obvious: I want to keep the information regarding the URL of the backend server in a JSON file - And the global service should return the server so this can be used in any method of the search service.

问题是:DoGeneralSearch()方法在全局服务能够解析任务以读取JSON文件并返回结果之前执行.因此，我有一个this.server =订阅服务器{isUnsubscribed:false，syncErrorValue:null，syncErrorThrown:false，syncErrorThrowable:false，isStopped:false…}，而不是结果本身.

The problem is: the DoGeneralSearch() method executes before the global service is capable to resolve the task to read the JSON file and return the result. So, I've a this.server = Subscriber {isUnsubscribed: false, syncErrorValue: null, syncErrorThrown: false, syncErrorThrowable: false, isStopped: false…} instead the result itself.

我需要找到一些方法来防止在解析完this.server变量后立即执行方法DoGeneralSearch.

I need to find some how to prevent the method DoGeneralSearch be executed just after resolved the this.server variable.

有什么建议吗?

推荐答案

我认为您可以在应用程序启动时预先加载此类提示.为此，您可以利用APP_INITIALIZER服务.在实际启动之前，应用程序将等待返回的诺言得到解决.

I think that you could preload such hints at the application startup. For this, you could leverage the APP_INITIALIZER service. The application will wait for the returned promise to be resolved before actually starting.

以下是示例:

provide(APP_INITIALIZER, {
  useFactory: (service:GlobalService) => () => service.load(),
  deps:[GlobalService, HTTP_PROVIDERS], multi: true
})

load方法想要这样的东西:

The load method would like something like that:

load():Promise<Site> {
  var promise = this.http.get('config.json').map(res => res.json()).toPromise();
  promise.then(config => this.devServer = config.devServer);
  return promise;
}

然后，您可以直接(同步)使用devServer ...

Then you can directly use the devServer (synchronously)...

有关更多详细信息，请参见github上的此问题:

See this issue on github for more details:

• https://github.com/angular/angular/issues/9047

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