How to pass data between two components in Angular 2

Parent to Child: Sharing Data via Input This is probably the most common and straightforward method of sharing data. It works by using the @Input() decorator to allow data to be passed via the template.

Child to Parent: Sharing Data via ViewChild ViewChild allows a one component to be injected into another, giving the parent access to its attributes and functions. One caveat, however, is that child won’t be available until after the view has been initialized. This means we need to implement the AfterViewInit lifecycle hook to receive the data from the child.

Child to Parent: Sharing Data via Output() and EventEmitter Another way to share data is to emit data from the child, which can be listed to by the parent. This approach is ideal when you want to share data changes that occur on things like button clicks, form entires, and other user events.

In the parent, we create a function to receive the message and set it equal to the message variable.

In the child, we declare a messageEvent variable with the Output decorator and set it equal to a new event emitter. Then we create a function named sendMessage that calls emit on this event with the message we want to send. Lastly, we create a button to trigger this function.

The parent can now subscribe to this messageEvent that’s outputted by the child component, then run the receive message function whenever this event occurs.

Unrelated Components: Sharing Data with a Service When passing data between components that lack a direct connection, such as siblings, grandchildren, etc, you should you a shared service. When you have data that should always been in sync, I find the RxJS BehaviorSubject very useful in this situation.

You can also use a regular RxJS Subject for sharing data via the service, but here’s why I prefer a BehaviorSubject.

It will always return the current value on subscription - there is no need to call onnext It has a getValue() function to extract the last value as raw data. It ensures that the component always receives the most recent data. In the service, we create a private BehaviorSubject that will hold the current value of the message. We define a currentMessage variable handle this data stream as an observable that will be used by the components. Lastly, we create function that calls next on the BehaviorSubject to change its value.

The parent, child, and sibling components all receive the same treatment. We inject the DataService in the constructor, then subscribe to the currentMessage observable and set its value equal to the message variable.

Now if we create a function in any one of these components that changes the value of the message. when this function is executed the new data it’s automatically broadcast to all other components.

Reference: https://angularfirebase.com/lessons/sharing-data-between-angular-components-four-methods/

You can use angular 2 Inputs for passing data to a component. E.g in your child class, make an input variable using angular 2 @Input decorator.

import {Component, Input} from 'angular2/core';

@Component({
  selector: 'child',
  styles: [`
  `],
  template: `
  `
})
export class ChildComponent {
  @Input() valueToPass = 0;
}

In your parent component (i.e in which you are calling your child component, pass your parameter as follows:

<child [valueToPass] = "value"></child>

I recommend you reading this article on passing and receiving arguments between components (https://toddmotto.com/passing-data-angular-2-components-input).

You can transfer data using service.

Make a service that holds the data while you switch components. Below is an example.

import { Injectable } from '@angular/core';

@Injectable()
export class TransfereService {

  constructor(
    private router:Router,
    private companyServiceService:CompanyServiceService
  ) { }

  private data;

  setData(data){
    this.data = data;
  }

  getData(){
    let temp = this.data;
    this.clearData();
    return temp;
  }

  clearData(){
    this.data = undefined;
  }

}

Now Consider 2 components Sender and Reciever.

Senders code: This code sets the data to the service and navigates to the receiver.

import { Router } from '@angular/router';
import { TransfereService } from './services/transfer.service';

export class SenderComponent implements OnInit {         
  constructor(
    private transfereService:TransfereService,
    private router:Router) {}

  somefunction(data){
   this.transfereService.setData(data);
   this.router.navigateByUrl('/reciever');//as per router
 }
}

Reciever's Code: This code fetches the data from service and clears the data as well.

import { Router } from '@angular/router';
import { TransfereService } from './services/transfer.service';

export class RecieverComponent implements OnInit {  
 data = this.transfereService.getData();       
 constructor(
   private transfereService:TransfereService,
   private router:Router) {
      if(this.data){
        // do whatever needed
      }
      else{
        this.router.navigateByUrl('/sender');
      }
   }
}

You should check out Fireship Demo for the same. It's helpful.