Angular 2 — navigate through web pages without reloading a component that is common for those pages

Question

Here you can find an example app: http://ivan-khludov.com/

This is my root component:

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

@Component({
  selector: 'root',
  template: `
  <h1>My Dummy Angular App</h1>
  <router-outlet></router-outlet>
  <nav>
    <a routerLink="/section-1/1" routerLinkActive="active">Section 1 - Page 1</a>
    <span>||</span>
    <a routerLink="/section-1/2" routerLinkActive="active">Section 1 - Page 2</a>
    <span>||</span>
    <a routerLink="/section-2/1" routerLinkActive="active">Section 2 - Page 1</a>
    <span>||</span>
    <a routerLink="/section-2/2" routerLinkActive="active">Section 2 - Page 2</a>
  </nav>
  `
})

export class AppWrapper {

}

A component for section 1, page 1:

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

@Component({
  selector: 'secapagea',
  template: `
  <h2>Section 1 - Page 1</h2>
  <countera></countera>
  `
})

export class Section1Page1 {

}

Almost the same thing for section 1, page 2:

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

@Component({
  selector: 'secapageb',
  template: `
  <h2>Section 1 - Page 2</h2>
  <countera></countera>
  `
})

export class Section1Page2 {

}

A counter component:

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

@Component({
  selector: 'countera',
  template: `
  <div>Seconds elapsed: {{this.count}}</div>
  `
})

export class Section1Counter {

    count: number;

    constructor() {

        this.count = 0;

        setInterval(() => {

            this.count ++;

        }, 1000);

    }

}

Put the case that I opened the first page of the section. Is there a way to navigate to the second page of the same section without reloading the counter? I want to find a general solution for such navigation issues — it could be not a counter component but sidebar navigation or section heading or something else.

Answer 1

Yeah it is absolutely possible to write a Component which can handle multiple Routes without reconstructing the Component each time.

If you create a component which handles all pages together as defined with the following route:

const routes: Routes = [
  { path: 'section-1/:page', component: Section1PageX }
];

You can subscribe on the route parameter "page" and handle the page change within your Component. This prevents Angular2 from reconstructing the page Component each time.

@Component({
  selector: 'secapagea',
  template: `
  <h2>Section 1 - Page {{page}}</h2>
  <countera></countera>
  `
})
export Section1PageX {
  private page: string;

  constructor(private route: ActivatedRoute) {}

  ngOnInit() {
    this.sub = this.route.params.subscribe(params => {
       this.page = params['page'];
       //handle the page change
    });  
  }

  ngOnDestroy() {
    //unsubscribe when you leave the section
    this.sub.unsubscribe();
  }
}

So your Section1Counter Component will only be destroyed if you leave the entire section.

You can also read more about this in our Blog Post Angular 2 by Example

Answer 2

If understand correctly the question, I think you should simply put the Section1Counter component in the AppWrapper component template and remove it from SectionxPagey components. In this way you woul use the router-outlet to display the pages while the Section1Counter would remain the same instance. I hope this helps

Answer 3

There is a module ng2-cache which will allow you to cache a component into local storage and also provide rules for the caching. I think it should do what you are looking for.