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Routing and Navigation

The Angular Router enables navigation from one view to the next as users perform application tasks.

Overview

The browser is a familiar model of application navigation:

  • Enter a URL in the address bar and the browser navigates to a corresponding page.
  • Click links on the page and the browser navigates to a new page.
  • Click the browser's back and forward buttons and the browser navigates backward and forward through the history of pages you've seen.

The Angular Router ("the router") borrows from this model. It can interpret a browser URL as an instruction to navigate to a client-generated view. It can pass optional parameters along to the supporting view component that help it decide what specific content to present.

The Basics

<base href>

Most routing applications should add a <base> element to the index.html as the first child in the <head> tag to tell the router how to compose navigation URLs.

If the app folder is the application root, as it is for the sample application, set the href value exactly as shown here.

<base href="/">

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. It is in its own library package, @angular/router. Import what you need from it as you would from any other Angular package.

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

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.

Router outlet

The RouterOutlet is a directive from the router library that is used as a component. It acts as a placeholder that marks the spot in the template where the router should display the components for that outlet.

<router-outlet></router-outlet>

Router links

Now you have routes configured and a place to render them, but how do you navigate? The URL could arrive directly from the browser address bar. But most of the time you navigate as a result of some user action such as the click of an anchor tag.

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 (the link parameters array). The router resolves that array into a complete URL.

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 equals (=) contains a space-delimited string of CSS classes that the Router will add when this link is active (and remove 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.

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.

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