typescript - Accessing a property in a parent Component

Question

I have a property in a top level Component that is used data from a HTTP source like so (this is in a file called app.ts):

import {UserData} from './services/user-data/UserData';

Component({
    selector: 'app', // <app></app>
    providers: [...FORM_PROVIDERS],
    directives: [...ROUTER_DIRECTIVES],
    pipes: [],
    template: require('./app.html')
})
@RouteConfig([
    // stuff here
])

export class App {
    // Please note that UserData is an Injectable Service I have written
    userStatus: UserStatus;

    constructor(private userData: UserData) {
        this.userStatus = new UserStatus();
    }

    ngOnInit() {
        this.userData.getUserStatus()
            .subscribe(
            (status) => {
                this.userStatus = status; // I want to access this in my Child Components...
            },
            (err) => {console.log(err);},
            () => {console.log("User status complete");            }
        );
    }
}

Now, I have another Component that is a direct child of the top level Component and within it I would like to access the parent's property 'userStatus', here is the child:

Component({
    selector: 'profile',
    template: require('app/components/profile/profile.html'),
    providers: [],
    directives: [],
    pipes: []
})

export class Profile implements OnInit {
    constructor() {

    }

    ngOnInit() {
        // I want to have access with the parent App Component, 'userStatus' propety here... I only want to read this property
    }
}

Now in Angular 1.x this would be easy as I could reference $parent in my child controller or (ANTI PATTERN ALERT!!!) I could be so foolish to put this data in my $rootScope.

What would be the best way to access the parent in Angular 2?

Answer 1

There are different way:

• global service

  • see also
  • https://github.com/escardin/angular2-community-faq/blob/master/services.md#how-do-i-communicate-between-components-using-a-shared-service
  • Global Events in Angular 2
  • Plunker

• service shared by parent and injected to the child

  • similar to global service but listed in providers or viewProviders in the parent instead of boostrap(...) and only available to children of parent.

• parent injected to the child and accessed directly by the child

  • disadvantage: tight coupling

export class Profile implements OnInit {
constructor(@Host() parent: App) {
  parent.userStatus ...
}

• data-binding

export class Profile implements OnInit {
  @Input() userStatus:UserStatus;
  ...
}

<profile [userStatus]="userStatus">