TypeError: Cannot read property 'post' of undefined

Question

Hi i just want to use a simple function, http post to post my date to a page.I want the server be able to fetch the date i post.

import { Component, OnInit } from '@angular/core';
import { MarginServcies } from '../../services/MarginService';
import { Response } from '@angular/http';
import { Http} from '@angular/http';
//import { Ng2SmartTableModule, LocalDataSource } from 'ng2-smart-table';


@Component({
    selector: 'margin',
    template: require('./margin.component.html')
})


export class MarginComponent implements OnInit {
    public http: Http;
    public MarginList = [];
    public date: string;
    public userdate: string;
    pad(i: number) {
        return i < 10 ? '0' + i : i;
    }
    onClick($event: any, userdate) {
        userdate = this.date;
        //console.log(this.date);
        this.http.post('api/date', userdate).subscribe();
    }

    //get the current date as default
    ngOnInit() {
        const selectedDate = new Date();
        this.date = `${selectedDate.getFullYear()}-${this.pad(selectedDate.getMonth() + 1)}-${this.pad(selectedDate.getDate())}`;
    }

    public constructor(private marginService: MarginServcies) {

        //get Margindata from server
        this.marginService.getMargin().subscribe(results => {
            this.MarginList = results.json();
            //console.log(results.json());
        });


    }

}

This is my component. I am using webpack, angular 4. I want to use the post function inside the onClick() function. once I click i can post a date. Now i check the console.log() works fine. The erro is:

MarginComponent.html:15 ERROR TypeError: Cannot read property 'post' of undefined
    at MarginComponent.onClick (margin.component.ts:25)
    at Object.eval [as handleEvent] (MarginComponent.html:15)
    at handleEvent (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:22850)
    at callWithDebugContext (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:24142)
    at Object.debugHandleEvent [as handleEvent] (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:23730)
    at dispatchEvent (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:19750)
    at vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:20342
    at HTMLButtonElement.<anonymous> (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:27870)
    at ZoneDelegate.invokeTask (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:83738)
    at Object.onInvokeTask (vendor.js?v=8G5nuphpleAMB8hDVj0v8l9es64guglhqGWIwYdey3M:15077)

Could anyone help me with that? thanks!

Answer 1

Just by declaring public http: Http will not make Http provider instance available inside component. You have to inject http service inside constructor, that will bring http object.

public constructor(
    private marginService: MarginServcies, 
    private http: Http //<-- added Http service.
) {
 //your code as is
}

Remove the declaration of public http: Http(http declaration) from start of class public http: Http

Answer 2

Http is an Inbuilt Angular Provider from the angular http module

import { Http, Response } from '@angular/http';

So you have to inject this http service in to the constructor. Then Only angular framework resolve the dependency

export class YourService {
    constructor(private http: Http) {

    }