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canActivate
Interface that a class can implement to be a guard deciding if a route can be activated. If all guards return true, navigation will continue. If any guard returns false, navigation will be cancelled. If any guard returns a UrlTree, current navigation will be cancelled and a new navigation will be kicked off to the UrlTree returned from the guard.
The canActivate
guard decides if route can be navigated to, which results in the creation of the route's component.
To implement the guard, create a new class and implement the CanActivate
interface.
The interface can return a boolean (as a boolean, a promise, or an Observable) or the guard can navigate to another route.
If it returns a truthy value, the component will be created, otherwise it will not and the navigation gets canceled.
@Injectable({
providedIn: "root",
})
export class OnlyDigitsGuard implements CanActivate {
canActivate(
next: ActivatedRouteSnapshot,
state: RouterStateSnapshot
){
return /^\d+$/.test(next.params.id);
}
To guard a route, add the guard to the canActivate
property while declaring the routes in the application.
const routes: Routes = [
{
path: 'parent',
component: ParentComponent,
canActivate: [OnlyDigitsGuard],
},
]
canActivateChild
Interface that a class can implement to be a guard deciding if a child route can be activated. If all guards return true, navigation will continue. If any guard returns false, navigation will be cancelled. If any guard returns a UrlTree, current navigation will be cancelled and a new navigation will be kicked off to the UrlTree returned from the guard.
The canActivateChild
guard, serves the same purpose as the canActivate
guard and can prevent a route navigation.
The API to create the guard is the same, but for the canActivateChild
guard you have to implement the CanActivateChild
interface.
@Injectable({
providedIn: "root",
})
export class OnlyDigitsGuard implements CanActivateChild {
canActivateChild(
next: ActivatedRouteSnapshot,
state: RouterStateSnapshot
){
return /^\d+$/.test(next.params.id);
}
To add the guard to the routes, use the canActivateChild
property.
Doing this will guard all the children's routes.
const routes: Routes = [
{
path: "parent",
component: ParentComponent,
canActivateChild: [OnlyDigitsGuard],
children: [...],
},
];
The differences
-
canActivate
will only execute when the parent component is not yet created. For example, if we navigate to the parent route it will be called, if we then navigate to a child route it will not. If we directly navigate to the child route, thecanActivate
guard will also be executed. -
canActivateChild
will always be executed while navigating to/between child routes. For example, if we're at a child routechild/1
and we navigate tochild/2
, the guard will get executed. If we directly navigate to a child route, the guard will also get called. If we navigate to the parent route, thecanActivateChild
guard will not be fired. - because
canActivate
is guarding the parent route, the child parameters (and data) are not available on theActivatedRouteSnapshot
of thecanActivate
guard. To be able to access the child parameters, we have to drill down the child components on theRouterStateSnapshot
.
Nice to knows
- because the parent component gets created first, the
canActivate
guard will always be called first. - if we directly navigate to a child component and the child guard returns a falsy value then the parent component will also not be created, because the navigation is cancelled when one of the guards return a falsy value.
- when the
canActivate
guard returns a falsy value, then thecanActivateChild
guard will not be called. - the
canActivateChild
guard can be rewritten as acanActivate
guard on every child route.
Example application
Follow me on Twitter at @tim_deschryver | Subscribe to the Newsletter | Originally published on timdeschryver.dev.
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