Interface that classes can implement to be a data provider. A data provider class can be used with the router to resolve data during navigation. The interface defines a resolve() method that is invoked when the navigation starts. The router waits for the data to be resolved before the route is finally activated.

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interface Resolve<T> {
  resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<T> | Promise<T> | T
}

Description

The following example implements a resolve() method that retrieves the data needed to activate the requested route.

@Injectable({ providedIn: 'root' })
export class HeroResolver implements Resolve<Hero> {
  constructor(private service: HeroService) {}

  resolve(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<Hero>|Promise<Hero>|Hero {
    return this.service.getHero(route.paramMap.get('id'));
  }
}

Here, the defined resolve() function is provided as part of the Route object in the router configuration:

@NgModule({
  imports: [
    RouterModule.forRoot([
      {
        path: 'detail/:id',
        component: HeroDetailComponent,
        resolve: {
          hero: HeroResolver
        }
      }
    ])
  ],
  exports: [RouterModule]
})
export class AppRoutingModule {}

You can alternatively provide an in-line function with the resolve() signature:

export const myHero: Hero = {
  // ...
}

@NgModule({
  imports: [
    RouterModule.forRoot([
      {
        path: 'detail/:id',
        component: HeroComponent,
        resolve: {
          hero: 'heroResolver'
        }
      }
    ])
  ],
  providers: [
    {
      provide: 'heroResolver',
      useValue: (route: ActivatedRouteSnapshot, state: RouterStateSnapshot) => myHero
    }
  ]
})
export class AppModule {}

Further information is available in the Usage Notes...

Methods

Usage notes

When both guard and resolvers are specified, the resolvers are not executed until all guards have run and succeeded. For example, consider the following route configuration:

{
 path: 'base'
 canActivate: [BaseGuard],
 resolve: {data: BaseDataResolver}
 children: [
  {
    path: 'child',
    guards: [ChildGuard],
    component: ChildComponent,
    resolve: {childData: ChildDataResolver}
   }
 ]
}

The order of execution is: BaseGuard, ChildGuard, BaseDataResolver, ChildDataResolver.