angular-docs-cn/aio/content/tutorial/toh-pt5.md

@title Routing

@intro We add the Angular Router and learn to navigate among the views

@description We received new requirements for our Tour of Heroes application:

• Add a Dashboard view.
• Navigate between the Heroes and Dashboard views.
• Clicking on a hero in either view navigates to a detail view of the selected hero.
• Clicking a deep link in an email opens the detail view for a particular hero.

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

We'll add Angular’s Router to our app to satisfy these requirements.

The Routing and Navigation chapter covers the router in more detail than we will in this tutorial. Run the for this part.

Where We Left Off

Before we continue with our Tour of Heroes, let’s verify that we have the following structure after adding our hero service and hero detail component. If not, we’ll need to go back and follow the previous chapters. The application runs and updates automatically as we continue to build the Tour of Heroes.

Action plan

Here's our plan:

• Turn AppComponent into an application shell that only handles navigation
• Relocate the Heroes concerns within the current AppComponent to a separate HeroesComponent
• Add routing
• Create a new DashboardComponent
• Tie the Dashboard into the navigation structure

Routing is another name for navigation. The router is the mechanism for navigating from view to view.

Splitting the AppComponent

Our current app loads AppComponent and immediately displays the list of heroes.

Our revised app should present a shell with a choice of views (Dashboard and Heroes) and then default to one of them.

The AppComponent should only handle navigation. Let's move the display of Heroes out of AppComponent and into its own HeroesComponent.

HeroesComponent

AppComponent is already dedicated to Heroes. Instead of moving anything out of AppComponent, we'll just rename it HeroesComponent and create a new AppComponent shell separately.

The steps are to rename:

• app.component.ts file to heroes.component.ts
• AppComponent class to HeroesComponent (rename locally, only in this file)
• Selector my-app to my-heroes

Create AppComponent

The new AppComponent will be the application shell. It will have some navigation links at the top and a display area below for the pages we navigate to.

The initial steps are:

• Create the file src/app/app.component.ts.
• Define an exported AppComponent class.
• Add an @Component !{_decorator} above the class with a my-app selector.
• Move the following from HeroesComponent to AppComponent:
  • title class property
  • @Component template <h1> element, which contains a binding to title
• Add a <my-heroes> element to the app template just below the heading so we still see the heroes.
• Add HeroesComponent to the !{_declsVsDirectives} !{_array} of !{_AppModuleVsAppComp} so Angular recognizes the <my-heroes> tags.
• Add HeroService to the providers !{_array} of !{_AppModuleVsAppComp} because we'll need it in every other view.
• Remove HeroService from the HeroesComponent providers !{_array} since it has been promoted.
• Add the supporting import statements for AppComponent.

Our first draft looks like this: The app still runs and still displays heroes. Our refactoring of AppComponent into a new AppComponent and a HeroesComponent worked! We have done no harm.

Add Routing

We're ready to take the next step. Instead of displaying heroes automatically, we'd like to show them after the user clicks a button. In other words, we'd like to navigate to the list of heroes.

We'll need the Angular Router.

{@a configure-routes} Routes tell the router which views to display when a user clicks a link or pastes a URL into the browser address bar.

Let's define our first route as a route to the heroes component: The !{_RoutesVsAtRouteConfig} !{_are} !{_an} !{_array} of route definitions. We have only one route definition at the moment but rest assured, we'll add more.

This route definition has the following parts:

• path: the router matches this route's path to the URL in the browser address bar (!{_routePathPrefix}heroes).

**name**: the official name of the route; it *must* begin with a capital letter to avoid confusion with the *path* (`Heroes`).

- **component**: the component that the router should create when navigating to this route (`HeroesComponent`).

Learn more about defining routes with !{_RoutesVsAtRouteConfig} in the Routing chapter.

Router Outlet

If we paste the path, /heroes, into the browser address bar, the router should match it to the !{_heroesRoute} route and display the HeroesComponent. But where?

We have to tell it where by adding a <router-outlet> element to the bottom of the template. RouterOutlet is one of the directives provided by the !{_RouterModuleVsRouterDirectives}. The router displays each component immediately below the <router-outlet> as we navigate through the application.

Router Links

We don't really expect users to paste a route URL into the address bar. We add an anchor tag to the template which, when clicked, triggers navigation to the HeroesComponent.

The revised template looks like this: Refresh the browser. We see only the app title and heroes link. We don't see the heroes list.

The browser's address bar shows /. The route path to HeroesComponent is /heroes, not /. We don't have a route that matches the path /, so there is nothing to show. That's something we'll want to fix. We click the Heroes navigation link, the browser bar updates to /heroes, and now we see the list of heroes. We are navigating at last!

At this stage, our AppComponent looks like this.

{@example 'toh-pt5/ts/src/app/app.component.1.ts' region='v2'}

The AppComponent is now attached to a router and displaying routed views. For this reason and to distinguish it from other kinds of components, we call this type of component a Router Component.

Add a Dashboard

Routing only makes sense when we have multiple views. We need another view.

Create a placeholder DashboardComponent that gives us something to navigate to and from. We’ll come back and make it more useful later.

Configure the dashboard route

Go back to !{_appRoutingTsVsAppComp} and teach it to navigate to the dashboard.

Import the dashboard component and add the following route definition to the !{_RoutesVsAtRouteConfig} !{_array} of definitions.

!{_redirectTo}

We want the app to show the dashboard when it starts and we want to see a nice URL in the browser address bar that says /dashboard. Remember that the browser launches with / in the address bar.

Add navigation to the template

Finally, add a dashboard navigation link to the template, just above the Heroes link.

We nested the two links within <nav> tags. They don't do anything yet but they'll be convenient when we style the links a little later in the chapter. To see these changes in your browser, go to the application root (/) and reload. The app displays the dashboard and we can navigate between the dashboard and the heroes.

Dashboard Top Heroes

Let’s spice up the dashboard by displaying the top four heroes at a glance.

Replace the template metadata with a templateUrl property that points to a new template file.Create that file with this content:

{@example 'toh-pt5/ts/src/app/dashboard.component.1.html'}

We use *ngFor once again to iterate over a list of heroes and display their names. We added extra <div> elements to help with styling later in this chapter.

Share the HeroService

We'd like to re-use the HeroService to populate the component's heroes !{_array}.

Recall earlier in the chapter that we removed the HeroService from the providers !{_array} of HeroesComponent and added it to the providers !{_array} of !{_AppModuleVsAppComp}.

That move created a singleton HeroService instance, available to all components of the application. Angular will inject HeroService and we'll use it here in the DashboardComponent.

Get heroes

Open dashboard.component.ts and add the requisite import statements. Now implement the DashboardComponent class like this: We've seen this kind of logic before in the HeroesComponent:

• Define a heroes !{_array} property.
• Inject the HeroService in the constructor and hold it in a private !{_priv}heroService field.
• Call the service to get heroes inside the Angular ngOnInit lifecycle hook.

In this dashboard we cherry-pick four heroes (2nd, 3rd, 4th, and 5th) with the Array.slice method.

Refresh the browser and see four heroes in the new dashboard.

Navigate to Hero Details

Although we display the details of a selected hero at the bottom of the HeroesComponent, we don't yet navigate to the HeroDetailComponent in the three ways specified in our requirements:

1. from the Dashboard to a selected hero.
2. from the Heroes list to a selected hero.
3. from a "deep link" URL pasted into the browser address bar.

Adding a hero-detail route seems like an obvious place to start.

Routing to a hero detail

We'll add a route to the HeroDetailComponent in !{_appRoutingTsVsAppComp} where our other routes are configured.

The new route is a bit unusual in that we must tell the HeroDetailComponent which hero to show. We didn't have to tell the HeroesComponent or the DashboardComponent anything.

At the moment the parent HeroesComponent sets the component's hero property to a hero object with a binding like this.

<my-hero-detail [hero]="selectedHero"></my-hero-detail>

That clearly won't work in any of our routing scenarios. Certainly not the last one; we can't embed an entire hero object in the URL! Nor would we want to.

Parameterized route

We can add the hero's id to the URL. When routing to the hero whose id is 11, we could expect to see a URL such as this:

/detail/11

The /detail/ part of that URL is constant. The trailing numeric id part changes from hero to hero. We need to represent that variable part of the route with a parameter (or token) that stands for the hero's id.

Configure a Route with a Parameter

Here's the route definition we'll use. The colon (:) in the path indicates that :id is a placeholder to be filled with a specific hero id when navigating to the HeroDetailComponent. We're finished with the application routes.

We won't add a 'Hero Detail' link to the template because users don't click a navigation link to view a particular hero. They click a hero whether that hero is displayed on the dashboard or in the heroes list.

We'll get to those hero clicks later in the chapter. There's no point in working on them until the HeroDetailComponent is ready to be navigated to.

That will require an HeroDetailComponent overhaul.

Revise the HeroDetailComponent

Before we rewrite the HeroDetailComponent, let's review what it looks like now:

{@example 'toh-4/ts/src/app/hero-detail.component.ts'}

The template won't change. We'll display a hero the same way. The big changes are driven by how we get the hero. First, add the requisite imports: Let's have the !{_ActivatedRoute} service, the HeroService and the Location service injected into the constructor, saving their values in private fields: We tell the class that we want to implement the OnInit interface. The hero id is a number. Route parameters are always strings. So we convert the route parameter value to a number with the !{_str2int}.

Add HeroService.getHero

The problem with this bit of code is that HeroService doesn't have a getHero method! We better fix that quickly before someone notices that we broke the app.

Open HeroService and add a getHero method that filters the heroes list from getHeroes by id: Let's return to the HeroDetailComponent to clean up loose ends.

Find our way back

We can navigate to the HeroDetailComponent in several ways. How do we navigate somewhere else when we're done?

The user could click one of the two links in the AppComponent. Or click the browser's back button. We'll add a third option, a goBack method that navigates backward one step in the browser's history stack using the Location service we injected previously.

Going back too far could take us out of the application. That's acceptable in a demo. We'd guard against it in a real application, perhaps with the !{_CanDeactivateGuard}. Then we wire this method with an event binding to a Back button that we add to the bottom of the component template. Modifying the template to add this button spurs us to take one more incremental improvement and migrate the template to its own file, called hero-detail.component.html:

{@example 'toh-pt5/ts/src/app/hero-detail.component.html'}

We update the component metadata with a moduleId and a templateUrl pointing to the template file that we just created. Refresh the browser and see the results.

Select a Dashboard Hero

When a user selects a hero in the dashboard, the app should navigate to the HeroDetailComponent to view and edit the selected hero.

Although the dashboard heroes are presented as button-like blocks, they should behave like anchor tags. When hovering over a hero block, the target URL should display in the browser status bar and the user should be able to copy the link or open the hero detail view in a new tab.

To achieve this effect, reopen the dashboard.component.html and replace the repeated <div *ngFor...> tags with <a> tags. The opening <a> tag looks like this:

{@example 'toh-pt5/ts/src/app/dashboard.component.html' region='click'}

Notice the [routerLink] binding.

Top level navigation in the AppComponent template has router links set to fixed !{_pathVsName}s of the destination routes, "/dashboard" and "/heroes".

This time, we're binding to an expression containing a link parameters !{_array}. The !{_array} has two elements, the !{_pathVsName} of the destination route and a route parameter set to the value of the current hero's id.

The two !{_array} items align with the !{_pathVsName} and :id token in the parameterized hero detail route definition we added to !{_appRoutingTsVsAppComp} earlier in the chapter: Refresh the browser and select a hero from the dashboard; the app should navigate directly to that hero’s details.

Select a Hero in the HeroesComponent

Earlier we added the ability to select a hero from the dashboard. We'll do something similar in the HeroesComponent.

The HeroesComponent template exhibits a "master/detail" style with the list of heroes at the top and details of the selected hero below.

{@example 'toh-4/ts/src/app/app.component.ts' region='template'}

Our goal is to move the detail to its own view and navigate to it when the user decides to edit a selected hero.

Delete the <h1> at the top (we forgot about it during the AppComponent-to-HeroesComponent conversion).

Delete the last line of the template with the <my-hero-detail> tags.

We'll no longer show the full HeroDetailComponent here. We're going to display the hero detail on its own page and route to it as we did in the dashboard.

We'll throw in a small twist for variety. We are keeping the "master/detail" style but shrinking the detail to a "mini", read-only version. When the user selects a hero from the list, we don't go to the detail page. We show a mini-detail on this page instead and make the user click a button to navigate to the *full detail *page.

Add the mini-detail

Add the following HTML fragment at the bottom of the template where the <my-hero-detail> used to be: After clicking a hero, the user should see something like this below the hero list:

Format with the uppercase pipe

Notice that the hero's name is displayed in CAPITAL LETTERS. That's the effect of the uppercase pipe that we slipped into the interpolation binding. Look for it right after the pipe operator ( | ). Pipes are a good way to format strings, currency amounts, dates and other display data. Angular ships with several pipes and we can write our own.

Learn about pipes in the Pipes chapter.

Move content out of the component file

We are not done. We still have to update the component class to support navigation to the HeroDetailComponent when the user clicks the View Details button.

This component file is really big. Most of it is either template or CSS styles. It's difficult to find the component logic amidst the noise of HTML and CSS.

Let's migrate the template and the styles to their own files before we make any more changes:

1. Cut-and-paste the template contents into a new heroes.component.html file.
2. Cut-and-paste the styles contents into a new heroes.component.css file.
3. Set the component metadata's templateUrl and styleUrls properties to refer to both files.

. *Set* the `moduleId` property to `module.id` so that `templateUrl` and `styleUrls` are relative to the component.

The styleUrls property is !{_an} !{_array} of style file names (with paths). We could list multiple style files from different locations if we needed them.

Update the HeroesComponent class.

The HeroesComponent navigates to the HeroDetailComponent in response to a button click. The button's click event is bound to a gotoDetail method that navigates imperatively by telling the router where to go.

This approach requires some changes to the component class:

1. Import the router from the Angular router library
2. Inject the router in the constructor (along with the HeroService)
3. Implement gotoDetail by calling the router.navigate method Note that we're passing a two-element link parameters !{_array} — a path and the route parameter — to the router.navigate method just as we did in the [routerLink] binding back in the DashboardComponent. Here's the fully revised HeroesComponent class: Refresh the browser and start clicking. We can navigate around the app, from the dashboard to hero details and back, for heroes list to the mini-detail to the hero details and back to the heroes again. We can jump back and forth between the dashboard and the heroes.

We've met all of the navigational requirements that propelled this chapter.

Styling the App

The app is functional but pretty ugly. Our creative designer team provided some CSS files to make it look better.

A Dashboard with Style

The designers think we should display the dashboard heroes in a row of rectangles. They've given us ~60 lines of CSS for this purpose including some simple media queries for responsive design.

If we paste these ~60 lines into the component styles metadata, they'll completely obscure the component logic. Let's not do that. It's easier to edit CSS in a separate *.css file anyway.

Add a dashboard.component.css file to the !{_appDir} folder and reference that file in the component metadata's styleUrls !{_array} property like this:

Stylish Hero Details

The designers also gave us CSS styles specifically for the HeroDetailComponent.

Add a hero-detail.component.css to the !{_appDir} folder and refer to that file inside the styleUrls !{_array} as we did for DashboardComponent. Let's also remove the hero property @Input !{_decorator} and its import while we are at it.

Here's the content for the aforementioned component CSS files.

Style the Navigation Links

The designers gave us CSS to make the navigation links in our AppComponent look more like selectable buttons. We cooperated by surrounding those links in <nav> tags.

Add a app.component.css file to the !{_appDir} folder with the following content.

Global application styles

When we add styles to a component, we're keeping everything a component needs — HTML, the CSS, the code — together in one convenient place. It's pretty easy to package it all up and re-use the component somewhere else.

We can also create styles at the application level outside of any component.

Our designers provided some basic styles to apply to elements across the entire app. These correspond to the full set of master styles that we installed earlier during setup. Here is an excerpt: Create the file styles.css, if it doesn't exist already. Ensure that it contains the master styles given here.

If necessary, also edit index.html to refer to this stylesheet. Look at the app now. Our dashboard, heroes, and navigation links are styling!

Application structure and code

Review the sample source code in the for this chapter. Verify that we have the following structure:

Recap

The Road Behind

We travelled a great distance in this chapter

• We added the Angular Router to navigate among different components.
• We learned how to create router links to represent navigation menu items.
• We used router link parameters to navigate to the details of user selected hero.
• We shared the HeroService among multiple components.
• We moved HTML and CSS out of the component file and into their own files.
• We added the uppercase pipe to format data.

We refactored routes into a `Routing Module` that we import.

The Road Ahead

We have much of the foundation we need to build an application. We're still missing a key piece: remote data access.

In the next chapter, we’ll replace our mock data with data retrieved from a server using http.