Routing

There are new requirements for the Tour of Heroes app:

Add a Dashboard view.
Add the ability to navigate between the Heroes and Dashboard views.
When users click a hero name in either view, navigate to a detail view of the selected hero.
When users click a deep link in an email, open the detail view for a particular hero.

When you’re done, users will be able to navigate the app like this:

Add the AppRoutingModule

An Angular best practice is to load and configure the router in a separate, top-level module that is dedicated to routing and imported by the root AppModule.

By convention, the module class name is AppRoutingModule and it belongs in the app-routing.module.ts in the src/app folder.

Use the CLI to generate it.

ng generate module app-routing –flat –module=app

–flat puts the file in src/app instead of its own folder.
–module=app tells the CLI to register it in the imports array of the AppModule.

The generated file looks like this:

src/app/app-routing.module.ts (generated)

import { NgModule } from ‘@angular/core’;

import { CommonModule } from ‘@angular/common’;

@NgModule({

imports: [

CommonModule

declarations: []

})

export class AppRoutingModule { }

You generally don’t declare components in a routing module so you can delete the @NgModule.declarations array and delete CommonModule references too.

You’ll configure the router with Routes in the RouterModule so import those two symbols from the @angular/router library.

Add an @NgModule.exports array with RouterModule in it. Exporting RouterModule makes router directives available for use in the AppModule components that will need them.

AppRoutingModule looks like this now:

src/app/app-routing.module.ts (v1)

import { NgModule } from ‘@angular/core’;

import { RouterModule, Routes } from ‘@angular/router’;

@NgModule({

exports: [ RouterModule ]

})

export class AppRoutingModule {}

Add routes – Routes tell the router which view to display when a user clicks a link or pastes a URL into the browser address bar. A typical Angular Route has two properties:

path: a string that matches the URL in the browser address bar.
component: the component that the router should create when navigating to this route.

You intend to navigate to the HeroesComponent when the URL is something like localhost:4200/heroes. Import the HeroesComponent so you can reference it in a Route. Then define an array of routes with a single route to that component.

import { HeroesComponent }from ‘./heroes/heroes.component’;

const routes: Routes = [

{ path: ‘heroes’, component: HeroesComponent }

];

Once you’ve finished setting up, the router will match that URL to path: ‘heroes’ and display the HeroesComponent.

RouterModule.forRoot() – You first must initialize the router and start it listening for browser location changes.

Add RouterModule to the @NgModule.imports array and configure it with the routes in one step by calling RouterModule.forRoot() within the imports array, like this:

imports: [ RouterModule.forRoot(routes) ],

The method is called forRoot() because you configure the router at the application’s root level. The forRoot() method supplies the service providers and directives needed for routing, and performs the initial navigation based on the current browser URL.

Add RouterOutlet

Open the AppComponent template replace the <app-heroes> element with a <router-outlet> element.

src/app/app.component.html (router-outlet)

<h1>{{title}}</h1>

<router-outlet></router-outlet>

<app-messages></app-messages>

You removed <app-heroes> because you will only display the HeroesComponent when the user navigates to it. The <router-outlet> tells the router where to display routed views.

The RouterOutlet is one of the router directives that became available to the AppComponent because AppModule imports AppRoutingModule which exported RouterModule.

You should still be running with this CLI command.

ng serve

The browser should refresh and display the app title but not the list of heroes. Look at the browser’s address bar. The URL ends in /. The route path to HeroesComponent is /heroes.

Append /heroes to the URL in the browser address bar. You should see the familiar heroes master/detail view.

Add a navigation link (routerLink)

Users shouldn’t have to paste a route URL into the address bar. They should be able to click a link to navigate.

Add a <nav> element and, within that, an anchor element that, when clicked, triggers navigation to the HeroesComponent. The revised AppComponent template looks like this:

src/app/app.component.html (heroes RouterLink)

<h1>{{title}}</h1>

<nav>

<a routerLink=”/heroes”>Heroes</a>

</nav>

<router-outlet></router-outlet>

<app-messages></app-messages>

A routerLink attribute is set to “/heroes”, the string that the router matches to the route to HeroesComponent. The routerLink is the selector for the RouterLink directive that turns user clicks into router navigations. It’s another of the public directives in the RouterModule.

The browser refreshes and displays the app title and heroes link, but not the heroes list. Click the link. The address bar updates to /heroes and the list of heroes appears.

Make this and future navigation links look better by adding private CSS styles to app.component.css as listed in the final code review below.

Add a dashboard view

Routing makes more sense when there are multiple views. So far there’s only the heroes view.

Add a DashboardComponent using the CLI:

ng generate component dashboard

The CLI generates the files for the DashboardComponent and declares it in AppModule.

Replace the default file content in these three files as follows and then return for a little discussion:

src/app/dashboard/dashboard.component.html

<h3>Top Heroes</h3>

</div>

</a>

</div>

The template presents a grid of hero name links.

The *ngFor repeater creates as many links as are in the component’s heroes array.
The links are styled as colored blocks by the dashboard.component.css.
The links don’t go anywhere yet but they will shortly.

The class is similar to the HeroesComponent class.

It defines a heroes array property.
The constructor expects Angular to inject the HeroService into a private heroService property.
The ngOnInit() lifecycle hook calls getHeroes.

This getHeroes returns the sliced list of heroes at positions 1 and 5, returning only four of the Top Heroes (2nd, 3rd, 4th, and 5th).

getHeroes(): void {

this.heroService.getHeroes()

.subscribe(heroes => this.heroes = heroes.slice(1, 5));

}

Add the dashboard route – To navigate to the dashboard, the router needs an appropriate route.

Import the DashboardComponent in the AppRoutingModule.

src/app/app-routing.module.ts (import DashboardComponent)

import { DashboardComponent } from ‘./dashboard/dashboard.component’;

Add a route to the AppRoutingModule.routes array that matches a path to the DashboardComponent.

{ path: ‘dashboard’, component: DashboardComponent },

Add a default route – When the app starts, the browsers address bar points to the web site’s root. That doesn’t match any existing route so the router doesn’t navigate anywhere. The space below the <router-outlet> is blank.

To make the app navigate to the dashboard automatically, add the following route to the AppRoutingModule.Routes array.

{ path: ”, redirectTo: ‘/dashboard’, pathMatch: ‘full’ },

This route redirects a URL that fully matches the empty path to the route whose path is ‘/dashboard’.

After the browser refreshes, the router loads the DashboardComponent and the browser address bar shows the /dashboard URL.

Add dashboard link to the shell – The user should be able to navigate back and forth between the DashboardComponent and the HeroesComponent by clicking links in the navigation area near the top of the page.

Add a dashboard navigation link to the AppComponent shell template, just above the Heroes link.

src/app/app.component.html

<h1>{{title}}</h1>

<nav>

<a routerLink=”/dashboard”>Dashboard</a>

<a routerLink=”/heroes”>Heroes</a>

</nav>

<router-outlet></router-outlet>

<app-messages></app-messages>

After the browser refreshes you can navigate freely between the two views by clicking the links.

Navigating to hero details

The HeroDetailsComponent displays details of a selected hero. At the moment the HeroDetailsComponent is only visible at the bottom of the HeroesComponent

The user should be able to get to these details in three ways.

By clicking a hero in the dashboard.
By clicking a hero in the heroes list.
By pasting a “deep link” URL into the browser address bar that identifies the hero to display.

In this section, you’ll enable navigation to the HeroDetailsComponent and liberate it from the HeroesComponent.

Delete hero details from HeroesComponent – When the user clicks a hero item in the HeroesComponent, the app should navigate to the HeroDetailComponent, replacing the heroes list view with the hero detail view. The heroes list view should no longer show hero details as it does now.

Open the HeroesComponent template (heroes/heroes.component.html) and delete the <app-hero-detail> element from the bottom.

Clicking a hero item now does nothing. You’ll fix that shortly after you enable routing to the HeroDetailComponent.

Add a hero detail route – A URL like ~/detail/11 would be a good URL for navigating to the Hero Detail view of the hero whose id is 11. Open AppRoutingModule and import HeroDetailComponent.

src/app/app-routing.module.ts (import HeroDetailComponent)

import { HeroDetailComponent }from ‘./hero-detail/hero-detail.component’;

Then add a parameterized route to the AppRoutingModule.routes array that matches the path pattern to the hero detail view.

{ path: ‘detail/:id’, component: HeroDetailComponent },

The colon (:) in the path indicates that :id is a placeholder for a specific hero id.

At this point, all application routes are in place.

src/app/app-routing.module.ts (all routes)

const routes: Routes = [

{ path: ”, redirectTo: ‘/dashboard’, pathMatch: ‘full’ },

{ path: ‘dashboard’, component: DashboardComponent },

{ path: ‘detail/:id’, component: HeroDetailComponent },

{ path: ‘heroes’, component: HeroesComponent }

];

DashboardComponent hero links – The DashboardComponent hero links do nothing at the moment.

Now that the router has a route to HeroDetailComponent, fix the dashboard hero links to navigate via the parameterized dashboard route.

src/app/dashboard/dashboard.component.html (hero links)

<a *ngFor=”let hero of heroes” class=”col-1-4″

routerLink=”/detail/{{hero.id}}”>

</div>

</a>

You’re using Angular interpolation binding within the *ngFor repeater to insert the current iteration’s hero.id into each routerLink.

HeroesComponent hero links – The hero items in the HeroesComponent are <li> elements whose click events are bound to the component’s onSelect() method.

src/app/heroes/heroes.component.html (list with onSelect)

<li *ngFor=”let hero of heroes”

[class.selected]=”hero === selectedHero”

(click)=”onSelect(hero)”>

<span class=”badge”>{{hero.id}}</span> {{hero.name}}

</li>

</ul>

Strip the <li> back to just its *ngFor, wrap the badge and name in an anchor element (<a>), and add a routerLink attribute to the anchor that is the same as in the dashboard template

src/app/heroes/heroes.component.html (list with links)

<span class=”badge”>{{hero.id}}</span> {{hero.name}}

</a>

</li>

</ul>

You’ll have to fix the private stylesheet (heroes.component.css) to make the list look as it did before. Revised styles are in the final code review at the bottom of this guide.

Remove dead code (optional) – While the HeroesComponent class still works, the onSelect() method and selectedHero property are no longer used. It’s nice to tidy up and you’ll be grateful to yourself later. Here’s the class after pruning away the dead code.

src/app/heroes/heroes.component.ts (cleaned up)

export class HeroesComponent implements OnInit {

heroes: Hero[];

constructor(private heroService: HeroService) { }

ngOnInit() {

this.getHeroes();

}

getHeroes(): void {

this.heroService.getHeroes()

.subscribe(heroes => this.heroes = heroes);

}

Routable HeroDetailComponent

Previously, the parent HeroesComponent set the HeroDetailComponent.hero property and the HeroDetailComponent displayed the hero.

HeroesComponent doesn’t do that anymore. Now the router creates the HeroDetailComponent in response to a URL such as ~/detail/11.

The HeroDetailComponent needs a new way to obtain the hero-to-display.

Get the route that created it,
Extract the id from the route
Acquire the hero with that id from the server via the HeroService

Add the following imports:

src/app/hero-detail/hero-detail.component.ts

import { ActivatedRoute } from ‘@angular/router’;

import { Location } from ‘@angular/common’;

import { HeroService }from ‘../hero.service’;

Inject the ActivatedRoute, HeroService, and Location services into the constructor, saving their values in private fields:

constructor(

private route: ActivatedRoute,

private heroService: HeroService,

private location: Location

) {}

The ActivatedRoute holds information about the route to this instance of the HeroDetailComponent. This component is interested in the route’s bag of parameters extracted from the URL. The “id” parameter is the id of the hero to display.

The HeroService gets hero data from the remote server and this component will use it to get the hero-to-display.

The location is an Angular service for interacting with the browser. You’ll use it later to navigate back to the view that navigated here.

Extract the id route parameter – In the ngOnInit() lifecycle hook call getHero() and define it as follows.

ngOnInit(): void {

this.getHero();

}

getHero(): void {

const id = +this.route.snapshot.paramMap.get(‘id’);

this.heroService.getHero(id)

.subscribe(hero => this.hero = hero);

}

The route.snapshot is a static image of the route information shortly after the component was created. The paramMap is a dictionary of route parameter values extracted from the URL. The “id” key returns the id of the hero to fetch.

Route parameters are always strings. The JavaScript (+) operator converts the string to a number, which is what a hero id should be. The browser refreshes and the app crashes with a compiler error. HeroService doesn’t have a getHero() method. Add it now.

Add HeroService.getHero() – Open HeroService and add this getHero() method

src/app/hero.service.ts (getHero)

getHero(id: number): Observable<Hero> {

// TODO: send the message _after_ fetching the hero

this.messageService.add(`HeroService: fetched hero id=${id}`);

return of(HEROES.find(hero => hero.id === id));

}

Note the backticks ( ` ) that define a JavaScript template literal for embedding the id. Like getHeroes(), getHero() has an asynchronous signature. It returns a mock hero as an Observable, using the RxJS of() function.

You’ll be able to re-implement getHero() as a real Http request without having to change the HeroDetailComponent that calls it.

The browser refreshes and the app is working again. You can click a hero in the dashboard or in the heroes list and navigate to that hero’s detail view.

If you paste localhost:4200/detail/11 in the browser address bar, the router navigates to the detail view for the hero with id: 11, “Mr. Nice”.

Find the way back – By clicking the browser’s back button, you can go back to the hero list or dashboard view, depending upon which sent you to the detail view. It would be nice to have a button on the HeroDetail view that can do that.

Add a go back button to the bottom of the component template and bind it to the component’s goBack() method.

src/app/hero-detail/hero-detail.component.html (back button)

Add a goBack() method to the component class that navigates backward one step in the browser’s history stack using the Location service that you injected previously.

src/app/hero-detail/hero-detail.component.ts (goBack)

goBack(): void {

this.location.back();

}

Refresh the browser and start clicking. Users can navigate around the app, from the dashboard to hero details and back, from heroes list to the mini detail to the hero details and back to the heroes again.

You’ve met all of the navigational requirements that propelled this page.

Go back to Tutorial