Angular 2：@component装饰器中的指令和提供程序

Question

Hi i am new to Angular 2, i referred many other similar post but nothing helped me.

Below are my Queries

1. When to use Directives and providers parameters in @component decorator? Do i need to pass component inside any of this parameters while i import component

2. I made a http subscribe call inside oninit() but it never's gets called when page loads I get undefined value in console. how do i call it when a page loads.

 ngOnInit() { this.loginService.getLoginData() .subscribe(data => { this.loginData = data; this.loginDataLength = data.length; }); console.log(this.loginData); } 

3. how do i communicate between 2 components while routing?
4. What is the difference between Directive and Component

Answer 1

-- When to use Directives and providers parameters in @component decorator?

Directives , when you want to use directives , you can load those inside that , but that was in older version.

Providers , when you want to load services in your components or modules

-- First of all change your code to this :

ngOnInit() {
    this.loginService.getLoginData()
      .subscribe(data => {
        this.loginData = data;
        this.loginDataLength = data.length;
        console.log(this.loginData);
      });

  }

This is async call , so you will not get data in sequence , your console log will not called after http call finishes , it will be called as soon as the api called, so you have to log that inside subscribe method.

-- how do i communicate between 2 components while routing?

By using CommonService and provide it at route level or as per the project structure and your requirements.