42 KiB
In-app navigation: routing to views
In a single-page app, you change what the user sees by showing or hiding portions of the display that correspond to particular components, rather than going out to the server to get a new page. As users perform application tasks, they need to move between the different views that you have defined.
To handle the navigation from one view to the next, you use the Angular Router
.
The Router
enables navigation by interpreting a browser URL as an instruction to change the view.
To explore a sample app featuring the router's primary features, see the .
Prerequisites
Before creating a route, you should be familiar with the following:
- Basics of components
- Basics of templates
- An Angular app—you can generate a basic Angular app using the Angular CLI.
For an introduction to Angular with a ready-made app, see Getting Started. For a more in-depth experience of building an Angular app, see the Tour of Heroes tutorial. Both guide you through using component classes and templates.
{@a basics}
Generate an app with routing enabled
The following command uses the Angular CLI to generate a basic Angular app with an app routing module, called AppRoutingModule
, which is an NgModule where you can configure your routes.
The app name in the following example is routing-app
.
When generating a new app, the CLI prompts you to select CSS or a CSS preprocessor.
For this example, accept the default of CSS
.
Adding components for routing
To use the Angular router, an app needs to have at least two components so that it can navigate from one to the other. To create a component using the CLI, enter the following at the command line where first
is the name of your component:
Repeat this step for a second component but give it a different name.
Here, the new name is second
.
The CLI automatically appends Component
, so if you were to write first-component
, your component would be FirstComponentComponent
.
{@a basics-base-href}
<base href>
This guide works with a CLI-generated Angular app.
If you are working manually, make sure that you have <base href="/">
in the <head>
of your index.html file.
This assumes that the app
folder is the application root, and uses "/"
.
Importing your new components
To use your new components, import them into AppRoutingModule
at the top of the file, as follows:
import { FirstComponent } from './first/first.component'; import { SecondComponent } from './second/second.component';
{@a basic-route}
Defining a basic route
There are three fundamental building blocks to creating a route.
Import the AppRoutingModule
into AppModule
and add it to the imports
array.
The Angular CLI performs this step for you.
However, if you are creating an app manually or working with an existing, non-CLI app, verify that the imports and configuration are correct.
The following is the default AppModule
using the CLI with the --routing
flag.
- Import
RouterModule
andRoutes
into your routing module.
The Angular CLI performs this step automatically.
The CLI also sets up a Routes
array for your routes and configures the imports
and exports
arrays for @NgModule()
.
- Define your routes in your
Routes
array.
Each route in this array is a JavaScript object that contains two properties.
The first property, path
, defines the URL path for the route.
The second property, component
, defines the component Angular should use for the corresponding path.
- Add your routes to your application.
Now that you have defined your routes, you can add them to your application.
First, add links to the two components.
Assign the anchor tag that you want to add the route to the routerLink
attribute.
Set the value of the attribute to the component to show when a user clicks on each link.
Next, update your component template to include <router-outlet>
.
This element informs Angular to update the application view with the component for the selected route.
{@a route-order}
Route order
The order of routes is important because the Router
uses a first-match wins strategy when matching routes, so more specific routes should be placed above less specific routes.
List routes with a static path first, followed by an empty path route, which matches the default route.
The wildcard route comes last because it matches every URL and the Router
selects it only if no other routes match first.
{@a getting-route-information}
Getting route information
Often, as a user navigates your application, you want to pass information from one component to another.
For example, consider an application that displays a shopping list of grocery items.
Each item in the list has a unique id
.
To edit an item, users click an Edit button, which opens an EditGroceryItem
component.
You want that component to retrieve the id
for the grocery item so it can display the right information to the user.
You can use a route to pass this type of information to your application components. To do so, you use the ActivatedRoute interface.
To get information from a route:
- Import
ActivatedRoute
andParamMap
to your component.
<code-example path="router/src/app/heroes/hero-detail/hero-detail.component.ts" region="imports-route-info" header="In the component class (excerpt)">
</code-example>
These `import` statements add several important elements that your component needs.
To learn more about each, see the following API pages:
* [`Router`](api/router)
* [`ActivatedRoute`](api/router/ActivatedRoute)
* [`ParamMap`](api/router/ParamMap)
- Inject an instance of
ActivatedRoute
by adding it to your application's constructor:
<code-example path="router/src/app/heroes/hero-detail/hero-detail.component.ts" region="activated-route" header="In the component class (excerpt)">
</code-example>
-
Update the
ngOnInit() { this.route.queryParams.subscribe(params => { this.name = params['name']; }); }ngOnInit()
method to access theActivatedRoute
and track theid
parameter:
Note: The preceding example uses a variable, `name`, and assigns it the value based on the `name` parameter.
{@a wildcard-route-how-to}
Setting up wildcard routes
A well-functioning application should gracefully handle when users attempt to navigate to a part of your application that does not exist. To add this functionality to your application, you set up a wildcard route. The Angular router selects this route any time the requested URL doesn't match any router paths.
To set up a wildcard route, add the following code to your routes
definition.
{ path: '**', component: }
The two asterisks, **
, indicate to Angular that this routes
definition is a wildcard route.
For the component property, you can define any component in your application.
Common choices include an application-specific PageNotFoundComponent
, which you can define to display a 404 page to your users; or a redirect to your application's main component.
A wildcard route is the last route because it matches any URL.
For more detail on why order matters for routes, see Route order.
{@a 404-page-how-to}
Displaying a 404 page
To display a 404 page, set up a wildcard route with the component
property set to the component you'd like to use for your 404 page as follows:
The last route with the path
of **
is a wildcard route.
The router selects this route if the requested URL doesn't match any of the paths earlier in the list and sends the user to the PageNotFoundComponent
.
Setting up redirects
To set up a redirect, configure a route with the path
you want to redirect from, the component
you want to redirect to, and a pathMatch
value that tells the router how to match the URL.
In this example, the third route is a redirect so that the router defaults to the first-component
route.
Notice that this redirect precedes the wildcard route.
Here, path: ''
means to use the initial relative URL (''
).
For more details on pathMatch
see Spotlight on pathMatch
.
{@a nesting-routes}
Nesting routes
As your application grows more complex, you may want to create routes that are relative to a component other than your root component.
These types of nested routes are called child routes.
This means you're adding a second <router-outlet>
to your app, because it is in addition to the <router-outlet>
in AppComponent
.
In this example, there are two additional child components, child-a
, and child-b
.
Here, FirstComponent
has its own <nav>
and a second <router-outlet>
in addition to the one in AppComponent
.
A child route is like any other route, in that it needs both a path
and a component
.
The one difference is that you place child routes in a children
array within the parent route.
{@a using-relative-paths}
Using relative paths
Relative paths allow you to define paths that are relative to the current URL segment.
The following example shows a relative route to another component, second-component
.
FirstComponent
and SecondComponent
are at the same level in the tree, however, the link to SecondComponent
is situated within the FirstComponent
, meaning that the router has to go up a level and then into the second directory to find the SecondComponent
.
Rather than writing out the whole path to get to SecondComponent
, you can use the ../
notation to go up a level.
In addition to ../
, you can use ./
or no leading slash to specify the current level.
Specifying a relative route
To specify a relative route, use the NavigationExtras
relativeTo
property.
In the component class, import NavigationExtras
from the @angular/router
.
Then use relativeTo
in your navigation method.
After the link parameters array, which here contains items
, add an object with the relativeTo
property set to the ActivatedRoute
, which is this.route
.
The navigate()
arguments configure the router to use the current route as a basis upon which to append items
.
The goToItems()
method interprets the destination URI as relative to the activated route and navigates to the items
route.
Accessing query parameters and fragments
Sometimes, a feature of your application requires accessing a part of a route, such as a query parameter or a fragment. The Tour of Heroes app at this stage in the tutorial uses a list view in which you can click on a hero to see details. The router uses an id
to show the correct hero's details.
First, import the following members in the component you want to navigate from.
import { ActivatedRoute } from '@angular/router'; import { Observable } from 'rxjs'; import { switchMap } from 'rxjs/operators';
Next inject the activated route service:
constructor(private route: ActivatedRoute) {}Configure the class so that you have an observable, heroes$
, a selectedId
to hold the id
number of the hero, and the heroes in the ngOnInit()
, add the following code to get the id
of the selected hero.
This code snippet assumes that you have a heroes list, a hero service, a function to get your heroes, and the HTML to render your list and details, just as in the Tour of Heroes example.
ngOnInit() { this.heroes$ = this.route.paramMap.pipe( switchMap(params => { this.selectedId = Number(params.get('id')); return this.service.getHeroes(); }) ); }
Next, in the component that you want to navigate to, import the following members.
import { Router, ActivatedRoute, ParamMap } from '@angular/router'; import { Observable } from 'rxjs';
Inject ActivatedRoute
and Router
in the constructor of the component class so they are available to this component:
hero$: Observable;
constructor( private route: ActivatedRoute, private router: Router ) {}
ngOnInit() { const heroId = this.route.snapshot.paramMap.get('id'); this.hero$ = this.service.getHero(heroId); }
gotoItems(hero: Hero) { const heroId = hero ? hero.id : null; // Pass along the hero id if available // so that the HeroList component can select that item. this.router.navigate(['/heroes', { id: heroId }]); }
{@a lazy-loading}
Lazy loading
You can configure your routes to lazy load modules, which means that Angular only loads modules as needed, rather than loading all modules when the app launches. Additionally, you can preload parts of your app in the background to improve the user experience.
For more information on lazy loading and preloading see the dedicated guide Lazy loading NgModules.
Preventing unauthorized access
Use route guards to prevent users from navigating to parts of an app without authorization. The following route guards are available in Angular:
To use route guards, consider using component-less routes as this facilitates guarding child routes.
Create a service for your guard:
ng generate guard your-guardIn your guard class, implement the guard you want to use.
The following example uses CanActivate
to guard the route.
In your routing module, use the appropriate property in your routes
configuration.
Here, canActivate
tells the router to mediate navigation to this particular route.
For more information with a working example, see the routing tutorial section on route guards.
Link parameters array
A link parameters array holds the following ingredients for router navigation:
- The path of the route to the destination component.
- Required and optional route parameters that go into the route URL.
You can bind the RouterLink
directive to such an array like this:
The following is a two-element array when specifying a route parameter:
You can provide optional route parameters in an object, as in { foo: 'foo' }
:
These three examples cover the needs of an app with one level of routing. However, with a child router, such as in the crisis center, you create new link array possibilities.
The following minimal RouterLink
example builds upon a specified default child route for the crisis center.
Note the following:
- The first item in the array identifies the parent route (
/crisis-center
). - There are no parameters for this parent route.
- There is no default for the child route so you need to pick one.
- You're navigating to the
CrisisListComponent
, whose route path is/
, but you don't need to explicitly add the slash.
Consider the following router link that navigates from the root of the application down to the Dragon Crisis:
- The first item in the array identifies the parent route (
/crisis-center
). - There are no parameters for this parent route.
- The second item identifies the child route details about a particular crisis (
/:id
). - The details child route requires an
id
route parameter. - You added the
id
of the Dragon Crisis as the second item in the array (1
). - The resulting path is
/crisis-center/1
.
You could also redefine the AppComponent
template with Crisis Center routes exclusively:
In summary, you can write applications with one, two or more levels of routing. The link parameters array affords the flexibility to represent any routing depth and any legal sequence of route paths, (required) router parameters, and (optional) route parameter objects.
{@a browser-url-styles}
{@a location-strategy}
LocationStrategy
and browser URL styles
When the router navigates to a new component view, it updates the browser's location and history with a URL for that view. As this is a strictly local URL the browser won't send this URL to the server and will not reload the page.
Modern HTML5 browsers support history.pushState, a technique that changes a browser's location and history without triggering a server page request. The router can compose a "natural" URL that is indistinguishable from one that would otherwise require a page load.
Here's the Crisis Center URL in this "HTML5 pushState" style:
localhost:3002/crisis-center/Older browsers send page requests to the server when the location URL changes unless the change occurs after a "#" (called the "hash"). Routers can take advantage of this exception by composing in-application route URLs with hashes. Here's a "hash URL" that routes to the Crisis Center.
localhost:3002/src/#/crisis-center/The router supports both styles with two LocationStrategy
providers:
PathLocationStrategy
—the default "HTML5 pushState" style.HashLocationStrategy
—the "hash URL" style.
The RouterModule.forRoot()
function sets the LocationStrategy
to the PathLocationStrategy
, which makes it the default strategy.
You also have the option of switching to the HashLocationStrategy
with an override during the bootstrapping process.
For more information on providers and the bootstrap process, see Dependency Injection.
Choosing a routing strategy
You must choose a routing strategy early in the development of you project because once the application is in production, visitors to your site use and depend on application URL references.
Almost all Angular projects should use the default HTML5 style. It produces URLs that are easier for users to understand and it preserves the option to do server-side rendering.
Rendering critical pages on the server is a technique that can greatly improve perceived responsiveness when the app first loads. An app that would otherwise take ten or more seconds to start could be rendered on the server and delivered to the user's device in less than a second.
This option is only available if application URLs look like normal web URLs without hashes (#) in the middle.
<base href>
The router uses the browser's history.pushState for navigation.
pushState
allows you to customize in-app URL paths; for example, localhost:4200/crisis-center
.
The in-app URLs can be indistinguishable from server URLs.
Modern HTML5 browsers were the first to support pushState
which is why many people refer to these URLs as "HTML5 style" URLs.
HTML5 style navigation is the router default. In the LocationStrategy and browser URL styles section, learn why HTML5 style is preferable, how to adjust its behavior, and how to switch to the older hash (#) style, if necessary.
You must add a <base href> element to the app's index.html
for pushState
routing to work.
The browser uses the <base href>
value to prefix relative URLs when referencing CSS files, scripts, and images.
Add the <base>
element just after the <head>
tag.
If the app
folder is the application root, as it is for this application,
set the href
value in index.html
as shown here.
HTML5 URLs and the <base href>
The guidelines that follow will refer to different parts of a URL. This diagram outlines what those parts refer to:
foo://example.com:8042/over/there?name=ferret#nose
\_/ \______________/\_________/ \_________/ \__/
| | | | |
scheme authority path query fragment
While the router uses the HTML5 pushState style by default, you must configure that strategy with a <base href>
.
The preferred way to configure the strategy is to add a <base href> element tag in the <head>
of the index.html
.
Without that tag, the browser may not be able to load resources (images, CSS, scripts) when "deep linking" into the app.
Some developers may not be able to add the <base>
element, perhaps because they don't have access to <head>
or the index.html
.
Those developers may still use HTML5 URLs by taking the following two steps:
- Provide the router with an appropriate
APP_BASE_HREF
value. - Use root URLs (URLs with an
authority
) for all web resources: CSS, images, scripts, and template HTML files.
- The
<base href>
path
should end with a "/", as browsers ignore characters in thepath
that follow the right-most "/". - If the
<base href>
includes aquery
part, thequery
is only used if thepath
of a link in the page is empty and has noquery
. This means that aquery
in the<base href>
is only included when usingHashLocationStrategy
. - If a link in the page is a root URL (has an
authority
), the<base href>
is not used. In this way, anAPP_BASE_HREF
with an authority will cause all links created by Angular to ignore the<base href>
value. - A fragment in the
<base href>
is never persisted.
For more complete information on how <base href>
is used to construct target URIs, see the RFC section on transforming references.
{@a hashlocationstrategy}
HashLocationStrategy
You can use HashLocationStrategy
by providing the useHash: true
in an object as the second argument of the RouterModule.forRoot()
in the AppModule
.
Router Reference
The folllowing sections highlight some core router concepts.
{@a basics-router-imports}
Router imports
The Angular Router is an optional service that presents a particular component view for a given URL.
It is not part of the Angular core and thus is in its own library package, @angular/router
.
Import what you need from it as you would from any other Angular package.
For more on browser URL styles, see LocationStrategy
and browser URL styles.
{@a basics-config}
Configuration
A routed Angular application has one singleton instance of the Router
service.
When the browser's URL changes, that router looks for a corresponding Route
from which it can determine the component to display.
A router has no routes until you configure it.
The following example creates five route definitions, configures the router via the RouterModule.forRoot()
method, and adds the result to the AppModule
's imports
array.
{@a example-config}
The appRoutes
array of routes describes how to navigate.
Pass it to the RouterModule.forRoot()
method in the module imports
to configure the router.
Each Route
maps a URL path
to a component.
There are no leading slashes in the path.
The router parses and builds the final URL for you, which allows you to use both relative and absolute paths when navigating between application views.
The :id
in the second route is a token for a route parameter.
In a URL such as /hero/42
, "42" is the value of the id
parameter.
The corresponding HeroDetailComponent
uses that value to find and present the hero whose id
is 42.
The data
property in the third route is a place to store arbitrary data associated with
this specific route.
The data property is accessible within each activated route. Use it to store items such as page titles, breadcrumb text, and other read-only, static data.
You can use the resolve guard to retrieve dynamic data.
The empty path in the fourth route represents the default path for the application—the place to go when the path in the URL is empty, as it typically is at the start.
This default route redirects to the route for the /heroes
URL and, therefore, displays the HeroesListComponent
.
If you need to see what events are happening during the navigation lifecycle, there is the enableTracing
option as part of the router's default configuration.
This outputs each router event that took place during each navigation lifecycle to the browser console.
Use enableTracing
only for debugging purposes.
You set the enableTracing: true
option in the object passed as the second argument to the RouterModule.forRoot()
method.
{@a basics-router-outlet}
Router outlet
The RouterOutlet
is a directive from the router library that is used like a component.
It acts as a placeholder that marks the spot in the template where the router should
display the components for that outlet.
Given the configuration above, when the browser URL for this application becomes /heroes
, the router matches that URL to the route path /heroes
and displays the HeroListComponent
as a sibling element to the RouterOutlet
that you've placed in the host component's template.
{@a basics-router-links}
{@a router-link}
Router links
To navigate as a result of some user action such as the click of an anchor tag, use RouterLink
.
Consider the following template:
The RouterLink
directives on the anchor tags give the router control over those elements.
The navigation paths are fixed, so you can assign a string to the routerLink
(a "one-time" binding).
Had the navigation path been more dynamic, you could have bound to a template expression that returned an array of route link parameters; that is, the link parameters array. The router resolves that array into a complete URL.
{@a router-link-active}
Active router links
The RouterLinkActive
directive toggles CSS classes for active RouterLink
bindings based on the current RouterState
.
On each anchor tag, you see a property binding to the RouterLinkActive
directive that looks like routerLinkActive="..."
.
The template expression to the right of the equal sign, =
, contains a space-delimited string of CSS classes that the Router adds when this link is active (and removes when the link is inactive).
You set the RouterLinkActive
directive to a string of classes such as [routerLinkActive]="'active fluffy'"
or bind it to a component property that returns such a string.
Active route links cascade down through each level of the route tree, so parent and child router links can be active at the same time.
To override this behavior, you can bind to the [routerLinkActiveOptions]
input binding with the { exact: true }
expression. By using { exact: true }
, a given RouterLink
will only be active if its URL is an exact match to the current URL.
{@a basics-router-state}
Router state
After the end of each successful navigation lifecycle, the router builds a tree of ActivatedRoute
objects that make up the current state of the router. You can access the current RouterState
from anywhere in the application using the Router
service and the routerState
property.
Each ActivatedRoute
in the RouterState
provides methods to traverse up and down the route tree to get information from parent, child and sibling routes.
{@a activated-route}
Activated route
The route path and parameters are available through an injected router service called the ActivatedRoute. It has a great deal of useful information including:
<th>
Description
</th>
<tr>
<td>
<code>parent</code>
</td>
<td>
The route's parent `ActivatedRoute` when this route is a [child route](guide/router-tutorial-toh#child-routing-component).
</td>
Property | |
---|---|
url
|
|
data
|
|
paramMap
|
|
queryParamMap
|
|
fragment
|
|
outlet
|
|
routeConfig
|
|
firstChild
|
|
children
|
|
Two older properties are still available, however, their replacements are preferable as they may be deprecated in a future Angular version.
-
params
: AnObservable
that contains the required and optional parameters specific to the route. UseparamMap
instead. -
queryParams
: AnObservable
that contains the query parameters available to all routes. UsequeryParamMap
instead.
Router events
During each navigation, the Router
emits navigation events through the Router.events
property.
These events range from when the navigation starts and ends to many points in between. The full list of navigation events is displayed in the table below.
<th>
Description
</th>
Router Event | |
---|---|
NavigationStart
|
|
RouteConfigLoadStart
|
|
RouteConfigLoadEnd
|
|
RoutesRecognized
|
|
GuardsCheckStart
|
|
ChildActivationStart
|
|
ActivationStart
|
|
GuardsCheckEnd
|
|
ResolveStart
|
|
ResolveEnd
|
|
ChildActivationEnd
|
|
ActivationEnd
|
|
NavigationEnd
|
|
NavigationCancel
|
|
NavigationError
|
|
Scroll
|
|
When you enable the enableTracing
option, Angular logs these events to the console.
For an example of filtering router navigation events, see the router section of the Observables in Angular guide.
Router terminology
Here are the key Router
terms and their meanings:
<th>
Router Part
</th>
<th>
Meaning
</th>
<td>
<code>Router</code>
</td>
<td>
Displays the application component for the active URL.
Manages navigation from one component to the next.
</td>
<td>
<code>RouterModule</code>
</td>
<td>
A separate NgModule that provides the necessary service providers
and directives for navigating through application views.
</td>
<td>
<code>Routes</code>
</td>
<td>
Defines an array of Routes, each mapping a URL path to a component.
</td>
<td>
<code>Route</code>
</td>
<td>
Defines how the router should navigate to a component based on a URL pattern.
Most routes consist of a path and a component type.
</td>
<td>
<code>RouterOutlet</code>
</td>
<td>
The directive (<code><router-outlet></code>) that marks where the router displays a view.
</td>
<td>
<code>RouterLink</code>
</td>
<td>
The directive for binding a clickable HTML element to a route. Clicking an element with a <code>routerLink</code> directive that is bound to a <i>string</i> or a <i>link parameters array</i> triggers a navigation.
</td>
<td>
<code>RouterLinkActive</code>
</td>
<td>
The directive for adding/removing classes from an HTML element when an associated <code>routerLink</code> contained on or inside the element becomes active/inactive.
</td>
<td>
<code>ActivatedRoute</code>
</td>
<td>
A service that is provided to each route component that contains route specific information such as route parameters, static data, resolve data, global query params, and the global fragment.
</td>
<td>
<code>RouterState</code>
</td>
<td>
The current state of the router including a tree of the currently activated routes together with convenience methods for traversing the route tree.
</td>
<td>
<b><i>Link parameters array</i></b>
</td>
<td>
An array that the router interprets as a routing instruction.
You can bind that array to a <code>RouterLink</code> or pass the array as an argument to the <code>Router.navigate</code> method.
</td>
<td>
<b><i>Routing component</i></b>
</td>
<td>
An Angular component with a <code>RouterOutlet</code> that displays views based on router navigations.
</td>