javascript - Angular 2 Sibling Component Communication

Question

I have a ListComponent. When an item is clicked in ListComponent, the details of that item should be shown in DetailComponent. Both are on the screen at the same time, so there's no routing involved.

How do I tell DetailComponent what item in ListComponent was clicked?

I've considered emitting an event up to the parent (AppComponent), and have the parent set the selectedItem.id on DetailComponent with an @Input. Or I could use a shared service with observable subscriptions.

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EDIT: Setting the selected item via event + @Input doesn't trigger the DetailComponent, though, in case I were to need to execute additional code. So I'm not sure this is an acceptable solution.

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But both of these methods seem far more complex than the Angular 1 way of doing things which was either through $rootScope.$broadcast or $scope.$parent.$broadcast.

With everything in Angular 2 being a component, I'm surprised there's not more information out there about component communication.

Is there another/more straightforward way to accomplish this?

Answer 1

Updated to rc.4: When trying to get data passed between sibling components in angular 2, The simplest way right now (angular.rc.4) is to take advantage of angular2's hierarchal dependency injection and create a shared service.

Here would be the service:

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

@Injectable()
export class SharedService {
    dataArray: string[] = [];

    insertData(data: string){
        this.dataArray.unshift(data);
    }
}

Now, here would be the PARENT component

import {Component} from '@angular/core';
import {SharedService} from './shared.service';
import {ChildComponent} from './child.component';
import {ChildSiblingComponent} from './child-sibling.component';
@Component({
    selector: 'parent-component',
    template: `
        <h1>Parent</h1>
        <div>
            <child-component></child-component>
            <child-sibling-component></child-sibling-component>
        </div>
    `,
    providers: [SharedService],
    directives: [ChildComponent, ChildSiblingComponent]
})
export class parentComponent{

} 

and its two children

child 1

import {Component, OnInit} from '@angular/core';
import {SharedService} from './shared.service'

@Component({
    selector: 'child-component',
    template: `
        <h1>I am a child</h1>
        <div>
            <ul *ngFor="#data in data">
                <li>{{data}}</li>
            </ul>
        </div>
    `
})
export class ChildComponent implements OnInit{
    data: string[] = [];
    constructor(
        private _sharedService: SharedService) { }
    ngOnInit():any {
        this.data = this._sharedService.dataArray;
    }
}

child 2 (It's sibling)

import {Component} from 'angular2/core';
import {SharedService} from './shared.service'

@Component({
    selector: 'child-sibling-component',
    template: `
        <h1>I am a child</h1>
        <input type="text" [(ngModel)]="data"/>
        <button (click)="addData()"></button>
    `
})
export class ChildSiblingComponent{
    data: string = 'Testing data';
    constructor(
        private _sharedService: SharedService){}
    addData(){
        this._sharedService.insertData(this.data);
        this.data = '';
    }
}

NOW: Things to take note of when using this method.

1. Only include the service provider for the shared service in the PARENT component and NOT the children.
2. You still have to include constructors and import the service in the children
3. This answer was originally answered for an early angular 2 beta version. All that has changed though are the import statements, so that is all you need to update if you used the original version by chance.