In this tutorial, we look at how to pass parameters or data to the Route in Angular. We look at how to define the route, which accepts the parameter. We then learn how to pass the parameters to the route using the routerLink directive. Finally, we learn how to retrieve the parameters using the ActivatedRoute Service. The parameters can be retrieved by using the either by snapshot method or by subscribe method. We take a look at both of these methods.
There are many scenarios, where you need to pass parameters to the route. For example, to navigate to the product detail View, we need to pass the product ID, so that component can retrieve it and display it to the user
Let us build on the Application we built in the Routing & Navigation tutorial and add a product detail page, which displays the product detail based on the Product ID passed in the URL. The code for this tutorial available on Github under the folder parameters.
In this article
How to Pass parameters to Angular Route
Defining the Route
Angular activates the route only if the navigated URL matches exactly
For example
1 2 3 | { path: 'product', component: ProductComponent }, |
The above route match only if the URL is “/product”
To retrieve the product details, our URL should look something like
/product/1
/product/2
Where second URL segment ( 1 and 2 ) being the Product id
To handle such scenario angular router allows us to include route parameters, where we can send any value for a URL segment
We can define parameter by adding forward slash followed colon and a placeholder (id) as shown below
1 2 3 | { path: 'product/:id', component: ProductDetailComponent } |
Now above path matches the URLs /product/1 , /product/2, etc.
If you have more than one parameter, then you can extend it by adding one more forward slash followed colon and a placeholder
1 2 3 | { path: 'product/:id/:id1/:id2', component: ProductDetailComponent } |
The name id, id1 & id2 are placeholders for parameters. We will use this name when retrieving the values of the parameters.
We, now need to provide both path and the route parameter routerLink directive.
This is done by adding the productID as the second element to the routerLink parameters array as shown below
1 2 3 | <a [routerLink]="['/Product', ‘2’]">{{product.name}} </a> |
Which translates to the URL /product/2
OR
1 2 3 | <a [routerLink]="['/Product', product.productID]">{{product.name}} </a> |
Which, dynamically takes the value of id from the product object.
Retrieve the parameter in the component
Finally, our component needs to extract the route parameter from the URL
This is done via the ActivatedRoute service from angular/router module to get the parameter value
ActviatedRoute
The ActivatedRoute is a service, which keeps track of the currently activated route associated with the loaded Component.
The ActivatedRoute class has a params property which is an array of the parameter values, indexed by name. We can use the params array to get the parameter value
To use ActivatedRoute, we need to import it in our component
1 2 3 | import { ActivatedRoute } from '@angular/router'; |
Then inject it into the component using dependency injection
1 2 3 | constructor(private _Activatedroute:ActivatedRoute) |
There are two ways in which you can use the ActivatedRoute to get the parameter value
- Using Snapshot
- Using observable
Using Snapshot
1 2 3 | this.id=this._Activatedroute.snapshot.params['id']; |
The snapshot property returns initial value of the route. You can then access the params array, to access the value of the id as shown above
Use this option, if you only need the initial value.
Using Observable
1 2 3 | _Activatedroute.params.subscribe(params => { this.id = params['id']; }); |
You can retrieve the value of id by subscribing to the params observable property of the activateRoute as shown above
Use this option if you expect the value of the parameter to change over time.
Why use observable
We usually retrieve the value of the parameter in the ngOninit life cycle hook, when the component initialised.
When the user navigates to the component again, the Angular does not create the new component but reuses the existing instance. In such circumstances, the ngOnInit method of the component is not called again. Hence you need a way to get the value of the parameter.
By subscribing to the observable params property, you will retrieve the latest value of the parameter and update the component accordingly.
The above difference is explained in our next tutorial Angular child routes tutorial.
Passing Parameters to Route: Example
Now let us add the product detail page to display the details of the selected Product.
Adding the Route
Open the app.routing.ts file.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | import { Routes } from '@angular/router'; import { HomeComponent} from './home.component' import { ContactComponent} from './contact.component' import { ProductComponent} from './product.component' import { ErrorComponent} from './error.component' import { ProductDetailComponent} from './product-detail.component' export const appRoutes: Routes = [ { path: 'home', component: HomeComponent }, { path: 'contact', component: ContactComponent }, { path: 'product', component: ProductComponent }, { path: 'product/:id', component: ProductDetailComponent }, { path: '', redirectTo: 'home', pathMatch: 'full' }, { path: '**', component: ErrorComponent } ]; |
We have added the following route to our routes array
1 2 3 | { path: 'product/:id', component: ProductDetailComponent }, |
We have added new route product followed by /:id and associated it with the ProductDetailComponent.
We need to change our product component
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | <h1>Product List</h1> <div class='table-responsive'> <table class='table'> <thead> <tr> <th>ID</th> <th>Name</th> <th>Price</th> </tr> </thead> <tbody> <tr *ngFor="let product of products;"> <td>{{product.productID}}</td> <td><a [routerLink]="['/product',product.productID]">{{product.name}} </a> </td> <td>{{product.price}}</td> </tr> </tbody> </table> </div> |
We have added product.productID as the second argument to the routerLink parameters array.
1 2 3 | <a [routerLink]="['/product',product.productID]">{{product.name}} </a> |
Product Details Page
We need a Product Detail page, which displays the selected Product.
To that, we need to add ProductDetailcomponet.ts under the app folder
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | import { Component, OnInit, OnDestroy } from '@angular/core'; import { Router,ActivatedRoute } from '@angular/router'; import { ProductService } from './product.service'; import { Product } from './product'; @Component({ templateUrl: './product-detail.component.html', }) export class ProductDetailComponent { product:Product; id; constructor(private _Activatedroute:ActivatedRoute, private _router:Router, private _productService:ProductService){ } /* Using snapshot */ ngOnInit() { this.id=this._Activatedroute.snapshot.params['id']; let products=this._productService.getProducts(); this.product=products.find(p => p.productID==this.id); } onBack(): void { this._router.navigate(['product']); } } |
First, we import router and ActivatedRoute from the angular router module
1 2 3 4 | import { Component, OnInit } from '@angular/core'; import { Router,ActivatedRoute } from '@angular/router'; |
In the constructor, we inject the activatedRoute, router service along with product Service
1 2 3 4 5 6 7 | constructor(private _Activatedroute:ActivatedRoute, private _router:Router, private _productService:ProductService){ } |
Finally, we use ngOninit life cycle hook to retrieve the value of the id parameter and use that value to retrieve the details of the product.
Note that we are using the snapshot method to retrieve the data.
1 2 3 4 5 6 7 | ngOnInit() { this.id=this._Activatedroute.snapshot.params['id']; let products=this._productService.getProducts(); this.product=products.find(p => p.productID==this.id); } |
The Template (Product-detail.component.html ) for displaying the product
1 2 3 4 5 6 7 8 9 | <h3>Product Details Page</h3> product : {{product.name}} price : {{ product.price}} <p> <a class='btn btn-default' (click)="onBack()">Back </a> </p> |
That’s it
Using Subscribe
We used snapshot method to retrieve the parameter in the ProductDetailcomponet.ts. To Subscribe to params remove the ngOnInit and replace it with the following code
We recommend you to use the subscribe method as it offers the benefit of responding to the parameter changes dynamically.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | sub; ngOnInit() { this.sub=this._Activatedroute.params.subscribe(params => { this.id = params['id']; let products=this._productService.getProducts(); this.product=products.find(p => p.productID==this.id); }); } ngOnDestroy() { this.sub.unsubscribe(); } |
Note that we unsubscribing in the OnDestroy life cycle hook, when the component is destroyed
ActivatedRoute
The ActivatedRoute service has a great deal of useful information including:
url: This property returns an array of Url Segment objects, each of which describes a single segment in the URL that matched the current route.
params: This property returns a Params object, which describes the URL parameters, indexed by name.
queryParams: This property returns a Params object, which describes the URL query parameters, indexed by name.
fragment: This property returns a string containing the URL fragment.
Snapshot: The initial snapshot of this route
data: An Observable that contains the data object provided for the route
Component: The component of the route. It’s a constant
outlet: The name of the RouterOutlet used to render the route. For an unnamed outlet, the outlet name is primary.
routeConfig: The route configuration used for the route that contains the origin path.
parent: an ActivatedRoute that contains the information from the parent route when using child routes.
firstChild: contains the first ActivatedRoute in the list of child routes.
children: contains all the child routes activated under the current route
pathFromRoot: The path from the root of the router state tree to this route
Conclusion
We looked at how to pass parameters or data to the Route. The parameters are passed to the route by using routerLink parameters in the routerLink directive. We retrieve the parameters from ActivatedRoute Service by reading params collection of the snapshot object or by subscribing to the params observable.
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