Uncaught (in promise): TypeError: Cannot read property 'component' of null

Question

Getting this error when trying to use nestet route in Angular 4:

ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'component' of null
TypeError: Cannot read property 'component' of null
    at PreActivation.webpackJsonp.../../../router/@angular/router.es5.js.PreActivation.traverseRoutes (http://localhost:4200/vendor.bundle.js:77976:71)
    at http://localhost:4200/vendor.bundle.js:77954:19
    at Array.forEach (native)
    at PreActivation.webpackJsonp.../../../router/@angular/router.es5.js.PreActivation.traverseChildRoutes (http://localhost:4200/vendor.bundle.js:77953:29)
    at PreActivation.webpackJsonp.../../../router/@angular/router.es5.js.PreActivation.traverseRoutes (http://localhost:4200/vendor.bundle.js:77985:22)

This is my routing code:

const appRoutes: Routes = [
    {
        path: '',
        component: HomeComponent
    },

    {
        path: 'sobre',
        component: SobreComponent
    },
    {
        path: 'c/:concurso', component: ConcursoItemComponent

        , children: [         
            {

                path: ':cargo',
                component: CargoItemComponent,


                children: [
                    {
                        path: ':disc',
                        component: DisciplinaItemComponent,
                        children: [{
                            path: ':assunto',
                            component: AssuntoItemComponent
                        }]
                    }
                ]

            }
        ]
    },

];

I want to make the following nested rules, each one using the variables to inform the nested components of each route:

/

/c/:concurso/

/c/:concurso/:cargo/

/c/:concurso/:cargo/:disc/

/c/:concurso/:cargo/:disc/:assunto

On each level, I will need all the upper variables to make the correct querying of the related objects of the API.

Thanks for any help!

Answer 1

As this article (https://angular-2-training-book.rangle.io/handout/routing/child_routes.html) states when dealing with child routes, just as you define a router-outlet for the root of your application, you must define a router-outlet for your parent component (in this case the ConcursoItemComponent. And technically also the CargoItemComponent & DisciplinaItemComponent) So you have 2 options.

• Define a router-outlet in the ConcursoItemComponent. This way the router will know where to load the child component (CargoItemComponent) when the user visits c/:concurso/:cargo
• Don't use child routes and instead make all of your routes at the top router level (root of the application)

{     path: 'c/:concurso,     component: ConcursoItemComponent }, {     path: 'c/:concurso/:cargo,     component: CargoComponent }, {     path: 'c/:concurso/:cargo/:disc,     component: DisciplinaItemComponent }, {     path: 'c/:concurso/:cargo/:disc/:assunto,     component: AssuntoItemComponent } 

This way the router will always insert the component into the router-outlet at the root of the application.

Answer 2

Just thought I'd add a comment for the benefit of those who stumble across this for the same reason I did. If your template uses conditional rendering, and those conditions are satisfied asynchronously, the router-outlet cannot be inside the conditional markup because the framework might try to render the markup before the condition is satisfied. For example:

<div *ngIf="someAsyncCall()">
   <header>{{some result from the async call}}</header>
   <router-outlet></router-outlet>
</div>

may fail depending on how quickly the async call finishes. It's always safer to include only the static parts of a the markup in the conditional rendering. As in:

<div *ngIf="someAsyncCall()">
    <header>{{some result from the async call}}</header>
</div>
<router-outlet></router-outlet>

I got bit by wrapping the entire page in a "busy indicator" directive which pretty much guaranteed that the router-outlet would not be available all the time. Seems obvious in hindsight, but....