Angular 2 http.post()不发送请求

Question

当我发帖请求时,角度2 http不发送此请求

this.http.post(this.adminUsersControllerRoute, JSON.stringify(user), this.getRequestOptions())

http帖子没有发送到服务器,但如果我发出这样的请求

this.http.post(this.adminUsersControllerRoute, JSON.stringify(user), this.getRequestOptions()).subscribe(r=>{});

这是有意的,如果有人可以解释我为什么？或者这是一个错误？

Answer 1

由于类的post方法Http返回一个observable,您需要订阅它以执行其初始化处理.可观察者很懒惰.

您应该查看此视频以获取更多详细信息:

• https://egghead.io/lessons/rxjs-rxjs-observables-vs-promises

Answer 2

如果要执行调用,则必须订阅返回的observable.

另请参阅Http文档.

总是订阅!

在HttpClient您对该方法返回的observable调用subscribe()之前,方法不会开始其HTTP请求.所有HttpClient方法都是如此.

该AsyncPipe订阅(和取消)为您自动.

从HttpClient方法返回的所有可观测量都是冷设计.HTTP请求的执行被推迟,让您可观察到的额外行动扩展,如tap与catchError任何实际发生之前.

调用subscribe(...)触发observable的执行并导致HttpClient组合并将HTTP请求发送到服务器.

您可以将这些可观察对象视为实际HTTP请求的蓝图.

实际上,每个都subscribe()启动了一个独立的,独立的observable执行.订阅两次会导致两个HTTP请求.

content_copy
const req = http.get<Heroes>('/api/heroes');
// 0 requests made - .subscribe() not called.
req.subscribe();
// 1 request made.
req.subscribe();
// 2 requests made.

Answer 3

Get方法不需要使用subscribe方法,但post方法需要subcribe.获取和发布示例代码如下.

import { Component, OnInit } from '@angular/core'
import { Http, RequestOptions, Headers } from '@angular/http'
import 'rxjs/add/operator/map'
import 'rxjs/add/operator/catch'
import { Post } from './model/post'
import { Observable } from "rxjs/Observable";

@Component({
    templateUrl: './test.html',
    selector: 'test'
})
export class NgFor implements OnInit {

    posts: Observable<Post[]>
    model: Post = new Post()

    /**
     *
     */
    constructor(private http: Http) {

    }

    ngOnInit(){
        this.list()
    }

    private list(){
        this.posts = this.http.get("http://localhost:3000/posts").map((val, i) => <Post[]>val.json())
    }

    public addNewRecord(){
        let bodyString = JSON.stringify(this.model); // Stringify payload
        let headers      = new Headers({ 'Content-Type': 'application/json' }); // ... Set content type to JSON
        let options       = new RequestOptions({ headers: headers }); // Create a request option

        this.http.post("http://localhost:3000/posts", this.model, options) // ...using post request
                         .map(res => res.json()) // ...and calling .json() on the response to return data
                         .catch((error:any) => Observable.throw(error.json().error || 'Server error')) //...errors if
                         .subscribe();
    }
}