5. Navigation
Last updated
Last updated
The Tour of Heroes application has new requirements:
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 can navigate the application like this:
In Angular the routes of an application are configured in the app.routes.ts
file.
Routes tell the Router which view to display when a user clicks a link or pastes a URL into the browser address bar.
Since app.routes.ts
already imports HeroesComponent
, you can use it in the routes
array:
path
A string that matches the URL in the browser address bar.
component
or loadComponent
The component that the router should create when navigating to this route.
This tells the router to match that URL to path: 'heroes'
and display the HeroesComponent
when the URL is something like localhost:4200/heroes
.
In the file app.config.ts
these routes are imported with provideRouter(routes)
.
Open the AppComponent
template and replace the <app-heroes>
element with a <router-outlet>
element.
The AppComponent
template no longer needs <app-heroes>
because the application only displays 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 the Angular router is imported with provideRouter
in the app.config.ts
file.
If you're not still serving your application, run ng serve
to see your application in the browser.
The browser should refresh and display the application 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 overview/detail view.
Remove /heroes
from the URL in the browser address bar. The browser should refresh and display the application title but not the list of heroes.
routerLink
Ideally, users should be able to click a link to navigate rather than pasting a route URL into the address bar.
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:
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 application title and heroes link, but not the heroes list.
Click the link. The address bar updates to /heroes
and the list of heroes appears.
Routing makes more sense when your application has more than one view, yet the Tour of Heroes application has only the heroes view.
To add a DashboardComponent
, run ng generate
as shown here:
ng generate
creates the files for the DashboardComponent
.
Replace the default content in these files as shown here:
The template presents a grid of hero name links.
The @for
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.
The class is like 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 Heroes two, three, four, and five.
To navigate to the dashboard, the router needs an appropriate route.
Add a route to the routes
array that matches a path to the DashboardComponent
.
When the application starts, the browser's 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 application navigate to the dashboard automatically, add the following route to the routes
array.
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.
The user should be able to navigate 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.
After the browser refreshes you can navigate freely between the two views by clicking the links.
The HeroDetailComponent
displays details of a selected hero. At the moment the HeroDetailComponent
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.
This section enables navigation to the HeroDetailComponent
and liberates it from the HeroesComponent
.
HeroesComponent
When the user clicks a hero in HeroesComponent
, the application 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 heroes/heroes.component.html
and delete the <app-hero-detail>
element from the bottom.
Clicking a hero item now does nothing. You can fix that after you enable routing to the HeroDetailComponent
.
A URL like ~/detail/11
would be a good URL for navigating to the Hero Detail view of the hero whose id
is 11
.
Add a parameterized route to the routes
array that matches the path pattern to the hero detail view.
The colon :
character in the path
indicates that :id
is a placeholder for a specific hero id
.
At this point, all application routes are in place.
DashboardComponent
hero linksThe DashboardComponent
hero links do nothing at the moment.
Now that the router has a route to HeroDetailComponent
, fix the dashboard hero links to navigate using the parameterized dashboard route.
You're using Angular interpolation binding within the @for
repeater to insert the current iteration's hero.id
into each routerLink
.
HeroesComponent
hero linksThe hero items in the HeroesComponent
are <li>
elements whose click events are bound to the component's onSelect()
method.
Be sure to fix the private style sheet in 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.
While the HeroesComponent
class still works, the onSelect()
method and selectedHero
property are no longer used.
It's nice to tidy things up for your future self. Here's the class after pruning away the dead code.
HeroDetailComponent
The parent HeroesComponent
used to 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/12
.
The HeroDetailComponent
needs a new way to get the hero to display. This section explains the following:
Get the route that created it
Extract the id
from the route
Get the hero with that id
from the server using the HeroService
Add the following imports:
Inject the ActivatedRoute
, HeroService
, and Location
services, saving their values in private fields:
The ActivatedRoute
holds information about the route to this instance of the HeroDetailComponent
. This component is interested in the route's 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 uses it to get the hero-to-display.
The location
is an Angular service for interacting with the browser. This service lets you navigate back to the previous view.
id
route parameterIn the ngOnInit()
lifecycle hook call getHero()
and define it as follows.
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 Number
function converts the string to a number, which is what a hero id
should be.
The browser refreshes and the application crashes with a compiler error. HeroService
doesn't have a getHero()
method. Add it now.
HeroService.getHero()
Open HeroService
and add the following getHero()
method with the id
after the getHeroes()
method:
Like getHeroes()
, getHero()
has an asynchronous signature. It returns a mock hero as an Observable
, using the RxJS of()
function.
You can rewrite getHero()
as a real Http
request without having to change the HeroDetailComponent
that calls it.
The browser refreshes and the application 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/12
in the browser address bar, the router navigates to the detail view for the hero with id: 12
, Dr Nice.
By clicking the browser's back button, you can go back to the previous page. This could be 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.
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 used to inject.
Refresh the browser and start clicking. Users can now navigate around the application using the new buttons.
The details look better when you add the private CSS styles to hero-detail.component.css
as listed in one of the "final code review" tabs below.
Here are the code files discussed on this page.
Routing
and HeroService
AppComponent
DashboardComponent
You added the Angular router to navigate among different components
You turned the AppComponent
into a navigation shell with <a>
links and a <router-outlet>
You configured the router in an app.routes.ts
You defined routes, a redirect route, and a parameterized route
You used the routerLink
directive in anchor elements
You refactored a tightly coupled main/detail view into a routed detail view
You used router link parameters to navigate to the detail view of a user-selected hero
You shared the HeroService
with other components
A typical Angular has two properties:
Remove the inner HTML of <li>
. Wrap the badge and name in an anchor <a>
element. Add a attribute to the anchor that's the same as in the dashboard template.
IMPORTANT:
The backtick ( `
) characters define a JavaScript for embedding the id
.