订阅Angular 2

我想要我的ngOnInit函数做下一件事：
? – 使用this.structureRequest.sendRequest()对某些数据进行http请求,这样可以正常工作,并且在收到数据后开始使用this.viewNodes()函数查看它.
我使用订阅,但它不起作用,我认为我做订阅功能有问题.请帮忙：)

> HomeComponent.ts

import {Component} from '@angular/core';
import {Observable} from 'rxjs/Observable';
import {StructureRequestService} from './StructureRequestService';


export class Content {


ok: boolean;
content = [];
}
@Component({
providers: [StructureRequestService],styleUrls: ['app/home/home.css'],templateUrl:'./app/home/homePageTemplate.html'

})

export class HomeComponent {
contentArray = [];
myRes: Content;
showAssigned:boolean = false;
showSubitems:boolean = false;
showUsers:boolean = false;

constructor(private structureRequest: StructureRequestService) {}

ngOnInit() {
this.structureRequest.sendRequest().subscribe( this.viewNodes());

}

viewNodes() {
this.myRes = this.structureRequest.result;
this.contentArray = this.myRes.content;
this.showAssigned = true;
 }
 }

2.这是http服务,http get工作正常,收到的所有数据：

import {Injectable} from '@angular/core';
import {Http,Response,Headers,RequestOptions} from '@angular/http';

import {Observable} from 'rxjs/Observable';

@Injectable ()
export class StructureRequestService {
result: Object;
//private myUrl = 'http://manny.herokuapp.com/audit/get/structure';
private myUrl = './app/home/nodes.json';  // local URL to structure APi
constructor (private http: Http) {
    //use XHR object
    let _build = (<any> http)._backend._browserXHR.build;
    (<any> http)._backend._browserXHR.build = () => {
        let _xhr =  _build();
        _xhr.withCredentials = true;
        return _xhr;
    };
}

sendRequest() {
    let body = JSON.stringify({});
    let headers = new Headers({ 'Content-Type': 'application/json'});
    let options = new RequestOptions({
        headers: headers
    });
     this.http.get(this.myUrl,options)
        .map((res: Response) => res.json())
        .subscribe(res => {this.result = res;
            return this.result; });
}
}

3.问题是制定同步步骤：接收数据,而不是查看数据.

this.structureRequest.sendRequest().subscribe( this.viewNodes());

this.structureRequest.sendRequest().subscribe(() => this.viewNodes());

this.structureRequest.sendRequest().subscribe((result) => this.viewNodes(result));

return this.http.get(this.myUrl,options) ...

return this.http.get(this.myUrl,options)
    .map((res: Response) => res.json())
    .subscribe(res => {this.result = res;
        return this.result; });

return this.http.get(this.myUrl,options)
    .map((res: Response) => res.json())
    .map(res => {
      this.result = res;
      return this.result; 
    });

return this.http.get(this.myUrl,options)
    .map((res: Response) => res.json())
    .do(res => {
      this.result = res;
    });