The ActivatedRoute snapshot does not function properly when used in the TypeScript class constructor

Question

The ActivatedRoute snapshot does not function properly when used in the TypeScript class constructor

Currently, I am encountering a challenge with TypeScript and Angular 2. The structure of my TS class is as follows:

'import { Component, OnInit } from '@angular/core';
import {ActivatedRoute} from '@angular/router';

@Component({
  selector: 'app-blogdetail',
  templateUrl: './blogdetail.component.html',
  styleUrls: ['./blogdetail.component.css']
})
export class BlogdetailComponent implements OnInit {

   blogId:any;
   title:any;

    constructor(private _activatedRoute:ActivatedRoute) {
    // Does not work
     // this.blogId = this._activatedRoute.snapshot.params['id'];
    //this.title= `This is blog detail for blogID:${this.blogId}`;

   }

  ngOnInit() {
      this.blogId = this._activatedRoute.snapshot.params['id'];
    this.title= `This is blog detail for blogID:${this.blogId}`;
  }

}'

I am trying to retrieve the route parameter in the ngOnit event. When I initially attempt to obtain the parameter in the TS class constructor, the value of the blogId variable is returned as undefined. Upon analyzing the sequence of events, it seems to resemble the flow illustrated in the image below: ![flow]https://i.stack.imgur.com/41fpe.png

Is it mandatory to always retrieve the activatedRoute snapshot values in ngOnIt?

angular typescript angular2-routing

Answer 1

Answer №1

That's correct. The issue arises when your component is initialized for your view, as only a new instance is created at that moment without activating the route, resulting in missing route parameters. Conversely, utilizing it in OnInit ensures that the route is activated and you are able to access the params. However, it is advisable to subscribe to the route params within your OnInit method to properly retrieve the params such as:

ngOnInit(){
    this.routeParamsSub = this.route.params.subscribe(routeParams => {
        this.blogId = routeParams['id']; 

       // implement additional logic here
    });
}

A similar approach can be found in this resource.

Answer 2

That's correct. The issue arises when your component is initialized for your view, as only a new instance is created at that moment without activating the route, resulting in missing route parameters. Conversely, utilizing it in OnInit ensures that the route is activated and you are able to access the params. However, it is advisable to subscribe to the route params within your OnInit method to properly retrieve the params such as:

ngOnInit(){
    this.routeParamsSub = this.route.params.subscribe(routeParams => {
        this.blogId = routeParams['id']; 

       // implement additional logic here
    });
}

A similar approach can be found in this resource.

Answer 3

Answer №2

During the creation of an object in angular, the params are not available.

Therefore, you should use it either within the ngOnInit method to assign it to a variable.

If you insist on having this code inside the constructor, you can use observables like so:

@Component({...})
class MyComponent {
  constructor(route: ActivatedRoute) {
    const id: Observable<string> = route.params.map(p => p.id);
    const url: Observable<string> = route.url.map(segments => segments.join(''));
    // route.data includes both `data` and `resolve`
    const user = route.data.map(d => d.user);
  }
}

However, using ActivatedRoute in the constructor is considered a bad practice in my opinion.

For more information, you can refer to the ActivatedRoute-interface documentation

Answer 4

During the creation of an object in angular, the params are not available.

Therefore, you should use it either within the ngOnInit method to assign it to a variable.

If you insist on having this code inside the constructor, you can use observables like so:

@Component({...})
class MyComponent {
  constructor(route: ActivatedRoute) {
    const id: Observable<string> = route.params.map(p => p.id);
    const url: Observable<string> = route.url.map(segments => segments.join(''));
    // route.data includes both `data` and `resolve`
    const user = route.data.map(d => d.user);
  }
}

However, using ActivatedRoute in the constructor is considered a bad practice in my opinion.

For more information, you can refer to the ActivatedRoute-interface documentation

The ActivatedRoute snapshot does not function properly when used in the TypeScript class constructor

Answer №1

Answer №2

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