Angular 2 如何使用路由器和 location.go() 检测后退按钮按下？

Question

I have built an app that uses router 3.0.0-beta.1 to switch between app sections. I also use location.go() to emulate the switch between subsections of the same page. I used <base href="/"> and a few URL rewrite rules in order to redirect all routes to index.html in case of page refresh. This allows the router to receive the requested subsection as a URL param. Basically I have managed to avoid using the HashLocationStrategy .

routes.ts

export const routes: RouterConfig = [
    {
        path: '',
        redirectTo: '/catalog',
        pathMatch: 'full'
    },
    {
        path: 'catalog',
        component: CatalogComponent
    },
    {
        path: 'catalog/:topCategory',
        component: CatalogComponent
    },
    {
        path: 'summary',
        component: SummaryComponent
    }
];

If I click on a subsection in the navigation bar 2 things happen:

• logation.go() updates the URL with the necessary string in order to indicate the current subsection
• A custom scrollTo() animation scrolls the page at the top of the requested subsection.

If I refresh the page I am using the previously defined route and extract the necessary parameter to restore scroll to the requested subsection.

this._activatedRoute.params
    .map(params => params['topCategory'])
    .subscribe(topCategory => {
        if (typeof topCategory !== 'undefined' &&
            topCategory !== null
        ) {
            self.UiState.startArrowWasDismised = true;
            self.UiState.selectedTopCategory = topCategory;
        }
    });

All works fine except when I click the back button. If previous page was a different section, the app router behaves as expected. However if the previous page/url was a subsection, the url changes to the previous one, but nothing happens in the UI. How can I detect if the back button was pressed in order to invoke the scrollTo() function to do it's job again?

Most answers I saw relly on the event onhashchange , but this event does not get fired in my app since I have no hash in the URL afterall...

Answer 1

I don't know if the other answers are dated, but neither of them worked well for me in Angular 7. What I did was add an Angular event listener by importing it into my component:

import { HostListener } from '@angular/core';

and then listening for popstate on the window object (as Adrian recommended):

  @HostListener('window:popstate', ['$event'])
  onPopState(event) {
    console.log('Back button pressed');
  }

This worked for me.

Answer 2

Another alternative for this issue would be to subscribe to the events emitted by the Angular Router service . Since we are dealing with routing, it seems to me that using Router events makes more sense.

constructor(router: Router) {
    router.events
      .subscribe((event: NavigationStart) => {
        if (event.navigationTrigger === 'popstate') {
          // Perform actions
        }
      });
}

I would like to note that popstate happens when pressing back and forward on the browser. So in order to do this efficiently, you would have to find a way to determine which one is occurring. For me, that was just using the event object of type NavigationStart which gives information about where the user is coming from and where they are going to.

Answer 3

To detect browser back button click import platformlocation from '@angular/common and place the below code in your constructor :

 constructor(location: PlatformLocation) {
     location.onPopState(() => {
        alert(window.location);
     }); }

Answer 4

Angular documentation states directly in PlatformLocation class...

• This class should not be used directly by an application developer.

I used LocationStrategy in the constructor

constructor(location: LocationStrategy) {
  location.onPopState(() => {
    alert(window.location);
  });
}

Answer 5

A great clean way is to import 'fromEvent' from rxjs and use it this way.

fromEvent(window, 'popstate')
  .subscribe((e) => {
    console.log(e, 'back button');
  });

Answer 6

This is the latest update for Angular 11

You have to first import NavigationStart from the angular router

import { NavigationStart, Router } from '@angular/router';

Then add the following code to the constructor

constructor(private router: Router) {
  router.events.forEach((event) => {
    if(event instanceof NavigationStart) {
      if (event.navigationTrigger === 'popstate') {
        /* Do something here */
      }
    }
  });
}

Answer 7

Using onpopstate event did the trick:

window.addEventListener('popstate',
    // Add your callback here
    () => self.events.scrollToTopCategory.emit({ categId: self.state.selectedTopCategory })
);

Answer 8

I agree with Adrian Moisa answer,

but you can use "more Angular 2 way" using class PlatformLocation by injecting to your component or service, then you can define onPopState callback this way:

this.location.onPopState(()=>{
  // your code here...
  this.logger.debug('onpopstate event');
});

Answer 9

Simpler way - Link

import { PlatformLocation } from '@angular/common';
import { NgbModal } from '@ng-bootstrap/ng-bootstrap';
...

constructor(
private platformLocation: PlatformLocation ,
private modalService: NgbModal
)
{
platformLocation.onPopState(() => this.modalService.dismissAll());
}

Answer 10

I honestly don't know your use case. And the thread is quite old. But this was the first hit on Google. And if someone else is looking for this with Angular 2 and ui-router (just as you are using).

It's not technically detecting the back button. It's more detecting whether you as a developer triggered the state change or whether the user updated the URL themselves.

You can add custom options to state changes, this can be done via uiSref and via stateService.go. In your transitions, you can check whether this option is set. (It won't be set on back button clicks and such).

Using ui-sref

    <a uiSref="destination-name" [uiOptions]="{custom: {viaSref: true}}">Bar</a>

Using state.go

import {StateService} from '@uirouter/core';

...

@Component(...)
export class MyComponent {

    constructor(
        private stateService: StateService
    ) {}

    public myAction(): void {
        this.stateService.go('destination-name', {}, {custom: {viaGo: true}});
    }
}

You can detect it in any transition hook, for example onSucces!

import {Transition, TransitionOptions, TransitionService} from '@uirouter/core';

...

@Component(...)
export class MyComponent implements OnInit {

    constructor(
        private transitionService: TransitionService
    ) {}

    public ngOnInit(): void {
        this.transitionService.onSuccess({}, (transition: Transition) => this.handleTransition(Transition));
    }

    private handleTransition(transition: Transition): void {
        let transitionOptions: TransitionOptions = transition.options();
        if (transitionOptions.custom?.viaSref) {
            console.log('viaSref!');
            return;
        }
        if (transitionOptions.custom?.viaGo) {
            console.log('viaGo!');
            return;
        }
        console.log('User transition?');
    }
}

Answer 11

You can check the size of "window.history", if the size is 1 you can't go back.

isCanGoBack(){
    window.history.length > 1;
}