How to share service data between components correctly in Angular 2

问题

I want to create a service to get data from .json file once and share it to multiple subscribers. But now with my solution number of requests to get data from .json file equals to a number of a subscibers for my service.

getconfig.service.ts

import {Injectable} from 'angular2/core';
import {Http, Response} from "angular2/http";

@Injectable()
export class ConfigService {
    config: any;
    http: Http;

    constructor(http: Http) {
        this.http = http;
        console.log('Inside service');
        this.config = this.http.get('/config.json');
    }

}

robotui.component.ts

...
import {ConnectionService} from '../services/connection.service';

@Component({
  ...
  providers: [HTTP_PROVIDERS, ConfigService, ConnectionService]
  ...
})

constructor(private _configService: ConfigService) {
  this._configService.config.subscribe((observer) => {
    console.log('Subscribe in RobotUI component', JSON.parse(observer._body));
  });
}

actual.photo.component.ts

import {Component} from 'angular2/core';
import {ConfigService} from '../services/getconfig.service';

@Component({
  ...
  providers: [ConfigService]
})

export class ActualPhotoComponent {

  constructor(private _configService: ConfigService) {
    this._configService.config.subscribe((observer) => {
      console.log('Subscribe in ActualPhoto component', JSON.parse(observer._body));
    });
  }

}

When i run it in my console i see:

So, there is get request for each subscibers. I want a solution when i get config.json file only once, save this info in a service and share it with multiple subscibers.

回答1:

That's because

@Component({
  ...
  providers: [ConfigService]  //<--- this creates service instance per component
})

To share data among controllers/components and to create single instance only, you have to inject your service into bootstrap function.

import {ConfigService } from './path to service';

bootstrap('AppCompoent',[configService])  //<----Inject here it will create a single instance only

In subscribing component,

robotui.component.ts

...
import {ConfigService} from '../services/getconfig.service';  //<----- Note this line here....
import {ConnectionService} from '../services/connection.service';

@Component({
  ...
  ...  // No providers needed anymore
  ...
})

constructor(private _configService: ConfigService) {
  this._configService.config.subscribe((observer) => {
    console.log('Subscribe in RobotUI component', JSON.parse(observer._body));
  });
}

actual.photo.component.ts

import {Component} from 'angular2/core';
import {ConfigService} from '../services/getconfig.service';

@Component({
  ...
  ...  // No providers needed anymore...
})

export class ActualPhotoComponent {

  constructor(private _configService: ConfigService) {
    this._configService.config.subscribe((observer) => {
      console.log('Subscribe in ActualPhoto component', JSON.parse(observer._body));
    });
  }

}

This is what you should do.

来源：https://stackoverflow.com/questions/37727990/how-to-share-service-data-between-components-correctly-in-angular-2

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