2020-03-24

Zoneless Angular Tip: How To Detect Activated Route Change

#Zoneless #Angular #ChangeDetection #Router #English

Although Angular allows us to use NoopNgZone to make an app zoneless, still some Angular modules are depending on Zone implicitly.

ngOnInit of Routed Component won’t be called!

I hit a problem when using Angular Router without Zone. Routing looks working but ngOnInit method of the routed component has not been executed.

image.png (188.7 kB)

It is because Angular Router depends on Zone in route activation. Technically, Router internally calls ChangeDetectorRef#markForCheck to re-render after route change. https://github.com/angular/angular/blob/master/packages/router/src/directives/router_outlet.ts#L142

As I wrote previously, markForCheck won’t trigger Change Detection without Zone.

Call detectChanges on (activate)

Here is a solution, maybe just a workaround.

@Component({
  selector: 'my-app',
  template: `
    <router-outlet (activate)="onRouteActivated()"></router-outlet>
`,
})
export class AppComponent {
  constructor(private cdRef: ChangeDetectorRef) {}

  onRouteActivated() {
  }
}

RouterOutlet component is exposing (activate) output. It emits events on route has been activated. So I can trigger Change Detection after route activation.

@Component({
  selector: 'my-app',
  template: `
    <router-outlet (activate)="onRouteActivated()"></router-outlet>
`,
})
export class AppComponent {
  constructor(private cdRef: ChangeDetectorRef) {}

  onRouteActivated() {
    // Call OnInit of routed component
    this.cdRef.detectChanges();
  }
}

Running example: https://ng-run.com/edit/pwwWzXxngYX0FUJDZIIj?open=app%2Fapp.component.ts

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