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Angular 2: Passing Data to Routes By @YFain | @ThingsExpo #IoT

Angular offers a directive RouteParams so a route can receive data from the parent component

In the previous blog I did a high-level overview of Angular 2 router and wrote a basic routing application that demonstrated displaying different components in a predefined area of the window. We often need not only display a component, but also pass some data to it.

For example, if we navigate from the Home to the Product Detail route we need to pass the product ID to the destination route. Angular offers a directive RouteParams so a route can receive data from the parent component. There is also a RouteData directive that can be used to pass additional data to a route from the @RouteConfig section. I’ll illustrate the use of both directives by modifying the app from the previous blog.

Using RouteParams
When the user navigates to the ProductDetail route, we need to pass the product ID to display details of the particular product. Let’s modify the code so the RootComponent can pass the product ID to ProductDetailComponent. The new version of this component will be called ProductDetailComponentParam and it’ll use the directive RouteParams:

import {Component} from 'angular2/angular2';
import {RouteParams} from 'angular2/router';

@Component({
selector: 'product',
template: `<h1 class="product">Product Detail for Product: {{productID}}</h1>` , // 1
styles: ['.product {background: cyan}']})
export class ProductDetailComponentParam {
productID: string;
constructor(params: RouteParams) { // 2
this.productID = params.get('id'); // 3
}

  1. Display the received product ID using binding.
  2. The constructor of this component requests Angular to inject the object RouteParams, which contains all parameters that are passed to this component. In TypeScript you just need to declare the argument specifying its type, and Angular will know how to instantiate and inject this object. We’ll cover dependency injection in details in Chapter 5.
  3. Get the value of the parameter named id and assign it to the class variable productID, which is used in template via binding.

Now let’s see how we can change @RouteConfig and router-link to ensure that the value of the product ID will be passed to the component ProdutDetailComponentParam if the user choses to go this route. We’ll do the changes in the file main.ts:

import 'reflect-metadata';
import 'zone.js'; // 1

import {Component, bootstrap, provide} from 'angular2/angular2';
import {HomeComponent} from './components/home'; // 2
import {ProductDetailComponentParam} from "./components/product_param";

import {RouteConfig, ROUTER_DIRECTIVES, ROUTER_PROVIDERS,
LocationStrategy, HashLocationStrategy} from 'angular2/router';

@Component({
selector: 'basic-routing',
template: `<a [router-link]="['/Home']">Home</a>
<a [router-link]="['/ProductDetail', {id: 1234}]">Product Details</a> // 3
<router-outlet></router-outlet>`,
directives: [ROUTER_DIRECTIVES]})
@RouteConfig([
{path: '/', component: HomeComponent, as: 'Home'},
{path: '/product/:id', component: ProductDetailComponentParam, as: 'ProductDetail' }]) // 4
class RootComponent {}

bootstrap(RootComponent, [ROUTER_PROVIDERS,
provide(LocationStrategy, {useClass: HashLocationStrategy})]);

  1. Angular asynchronously modifies the values of properties participated in binding. In our case, after the user choses to open the product detail component, the value of the variable productID changes and its bindings need to be updated. The library zone.js will automatically sync up all the bindings and watchers in the entire component tree of the application.
  2. I kept my components in the _components_ directory and need import them from there.
  3. This time there are two elements in the array given to router-link. The first one is the name of the route and the second is a JavaScript object containing a name/value pair that represents the parameter to be passed to the /ProductDetail route. For simplicity we’ve hardcoded the id to be 1234, but if we had a variable product pointing to the corresponding object, we could have written {id: product.id} here.
  4. The path property has an additional fragment /:id. The name of this URL fragment must match the name of the parameter property used in router-link. Angular will construct the URL fragment /product/1234 for this ProductDetail route. Note that we still use the same route name in router-link even though it points not to the ProductDetailComponent but to ProductDetailComponentParam.

The following screenshot shows how the product detail view will be rendered in the browser:

ch4_basic_routing_product_detail_param

Note the URL. Angular router replaced the path /product/:id with /product/1234.

Let’s overview the steps that Angular did under the hood for rendering the main page of the application:

  1. Check the the content of each router-link to find the corresponding routes configurations.
  2. Modify the URL fragments the parameters with actual values where specified.
  3. Build the actual <a href=””> tags that the browser understands.

The next screenshot shows a snapshot of the home page of our application with the Chrome Dev Tools panel open.

ch4_basic_routing_product_detail_href

Since the path property of the Home route contains just the slash, Angular simply removed it – a single slash base URL of the page. But the anchor under Product Details link is already converted into a regular HTML tag. When the user will click on the Product Details link, the router will attach a hash sign and add /product/1234 to the base URL so the absolute URL of the Product Detail view will become http://localhost:8080/#/product/1234.

Using RouteData
While most of the times parent components will be passing data to their children, Angular also offers a mechanism to pass additional data to components at the time of the route configuration. For example, besides the data that a component needs for implementing application logic, we may need to pass a flag indicating if the application runs in production environment or not. This can be done by using the data property of the @RouteConfig annotation. For example, our ProductDetail route can be configured as follows:

@RouteConfig([
{path: '/product/:id', component: ProductDetailComponentParam,
as: 'ProductDetail', data: {isProd: true}}])

Accordingly, the constructor of the ProductDetailComponent will need an extra argument of type RouteData:

export class ProductDetailComponentParam {
productID: string;
constructor(params: RouteParams, data: RouteData) {
this.productID = params.get('id');

console.log(`Is this prod environment: ${data.get('isProd')}`);
}
}

Passing data to a route with RouteData is not an alternative to RouteParams. While RouteParams is used to pass the data from one route to another using based on the user’s selections (e.g., show details of the selected product), RouteData can come handy when you need to pass some data to a route during the configuration phase, e.g. is it a production or QE environment, should the user have administrator’s privileges, or what URL of use for the product service.

To see this application in action follow this plank and press the button Run. For simplicity, all the code is located in one file main.ts. Also, I imported the dev version of Angular in the index.html that includes such libraries as zone.js and reflect-metadata, so there is no need to import them separately.

Stay tuned for more Angular 2 blogs. My other Angular-related blogs are here . Manning started publishing drafts of our book “Angular 2 Development with TypeScript“.

Read the original blog entry...

More Stories By Yakov Fain

Yakov Fain is a Java Champion and a co-founder of the IT consultancy Farata Systems and the product company SuranceBay. He wrote a thousand blogs (http://yakovfain.com) and several books about software development. Yakov authored and co-authored such books as "Angular 2 Development with TypeScript", "Java 24-Hour Trainer", and "Enterprise Web Development". His Twitter tag is @yfain

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