动态更新JSON数据

I am trying to get JSON data to my angular front end from php backend.Json data's first property "stock_price" changes randomly, but the JSON data's time property should be increment with seconds. Which means that,

{
stock_price: 19,
time: 1
}

next it should be

 {
stock_price: 26,
time: 2
}

like that.

When i try this exact php script with browser/postman , it updates in every page refresh/Post request as i expected.

But when i console it in an Angular app, the time property doesn't change. time is stick to 1.

What can i do, in order to get an updating json reply.

php file

<?php
header('Content-Type: application/json');

session_start();

$time = isset($_SESSION['time']) ? $_SESSION['time'] : 0;


$stock_price = rand(10,100);

$arr['stock_price'] = $stock_price;
$arr['time'] = ++$time;

echo json_encode($arr);

$_SESSION['time'] = $time;
?>

Angular app component file

export class AppComponent {


  ngOnInit(){
    this._helper.helperHelp()
    .subscribe(res => {
      console.log(res);
    })
  }

 constructor(private _helper:HelperService){
  setInterval(()=>{
    this.ngOnInit(); },4000); 
  }

 }

service class

export class HelperService {

  constructor(private _http:HttpClient) { }

  helperHelp(){
    return this._http.get("http://localhost/restPHP/restphp.php")
               .map(result =>result);
  }


}

You will have to pass time from Angular. You can send it as body if you are using POST otherwise in URL (in case of GET)

PHP

$time = isset($_GET['time']) ? $_GET['time'] : 0; // change to $_POST in case of POST

Angular component

export class AppComponent {
    stockData;
    constructor(private _helper:HelperService){

    }

    ngOnInit(){
        this.getDataFromServer();
        this.scheduleInterval();
    }

    scheduleInterval() {
        setInterval(this.getDataFromServer, 4000);
    }

    getDataFromServer() {
        let time = this.stockData ? this.stockData.time : 0;
        this._helper.helperHelp(time).subscribe(res => { //use time in your service
            this.stockData = res;
            console.log(this.stockData);
        });
    }
}

service

helperHelp(time) { 
    return this._http.get(`http://localhost/restPHP/restphp.php?time=${time}`).map(result =>result); 
}

Add the new value in session. currently, you are adding 0 every time. Add below code in any PHP file and try to reload every time.

session_start();
$time = isset($_SESSION['time']) ? $_SESSION['time'] : 0;
$arr['time'] = ++$time;
$_SESSION["time"] = $time;
echo json_encode($arr);