What
is an Angular 2 Service?
Angular 2 service is a class that encapsulates
some methods (GET/POST/PUT) and provides it result as a service for across your
application.
What
are the features of Angular 2 Service?
The Angular 2 is using services concept and it
provide the multiple features to us that are,
1.
Services are singleton objects.
2.
Services are capable of returning the
data in the form promises or observables.
3.
Service class is decorated with
Injectable decorator.
4.
The Injectable decorator is required
only if our service class is making use of some Angular injectable like Http, Response
and HttpModule service within it.
What
are the differences between Observables & Promises?
1.
Promise:- Promises are only called once and It can return
only a single value at a time and the Promises are not cancellable.
2.
Observables:- Observables handle multiple values over time and it can return multiple values and the Observables are cancellable.
3.
The Observables are more advanced
than Promises.
Steps
for creating an Angular 2 Service:-
There are four steps as,
1.
Import the injectable member i.e.
import {Injectable} from '@angular/core';
2.
Import the HttpModule, Http and
Response members’ i.e.
import { HttpModule, Http, Response } from '@angular/http';
3.
Add the @Injectable Decorator i.e. @Injectable()
4. Export to the
Service class i.e.
export class UserService {
constructor(private _http: Http) { }
}
Steps
for Calling an Angular 2 Service in the Angular 2 Component class:-
There are four steps to calling a service in
component as,
1.
Create or Import the Service to the
component class.
2.
Add it as a component provider.
3.
Include it through Dependency
Injection.
4.
Use the Service function in the component.
In
the below Example,
I hope this will help you to understand and
create the basic of Angular 2 service. I am creating a user service and this
user service returns the list of users.
After creating user service, I will use the user service
“getUsers()” method in the user component’s ngOnInit() method to load the returns user collections on
user screen.
I am also using the REST API Url (https://api.github.com/users/hadley/orgs)
and this RESTful API will returns the users.
app.module.ts
:-
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { UniversalModule } from 'angular2-universal';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
import { AppComponent } from './components/app/app.component';
import { UserComponent } from './components/user/user.component';
import { HeaderComponent } from './components/shared/header/header.component';
import { MenuComponent } from './components/menu/menu.component';
import { LoginComponent } from './components/login/login.component';
import { RegistrationComponent } from './components/registration/registration.component';
@NgModule({
bootstrap: [ AppComponent ],
declarations: [
AppComponent,
UserComponent,
HeaderComponent,
MenuComponent,
LoginComponent,
RegistrationComponent
],
imports: [
UniversalModule, // MUST BE FIRST IMPORT. THIS AUTOMATICALLY IMPORTS BROWSERMODULE,
HTTPMODULE, AND JSONPMODULE TOO.
RouterModule.forRoot([ //RouterModule.forRoot method in the module imports to configure
the router.
{ path: '', redirectTo: 'user', pathMatch: 'full' },
{ path: 'user/:id', component: UserComponent }, //HERE ID IS A ROUTE PARAMETER.
{ path: 'login', component: LoginComponent },
{ path: 'registration', component:
RegistrationComponent },
{ path: '**', redirectTo: 'user' }
]),
FormsModule,
ReactiveFormsModule
]
})
export class AppModule {
}
user.component.ts
and user.service.ts :-
import { Component, Injectable} from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpModule, Http, Response } from '@angular/http';
//BEGIN-REGION
- USERSERVICE
@Injectable()
export class UserService {
constructor(private _http:
Http) { }
getUsers(apiUrl) {
return this._http.get(apiUrl).map((data:
Response) => data.json());
}
}
//END
BEGIN - USERSERVICE
//BEGIN-REGION
- USERCOMPONENT
@Component({
selector: 'user',
templateUrl: './user.component.html',
styleUrls: ['./user.component.css'],
providers: [UserService]
})
export class UserComponent {
//USERS
DECLARATIONS.
users = [];
//FETCHING JSON
DATA FROM REST APIS
userRestApiUrl: string = 'https://api.github.com/users/hadley/orgs';
//HOME
COMPONENT CONSTRUCTOR
constructor(private
userService: UserService) { }
//GET USERS
SERVICE ON PAGE LOAD.
ngOnInit() {
this.userService.getUsers(this.userRestApiUrl).subscribe(data => this.users = data);
}
}
//END BEGIN – USERCOMPONENT
user.component.html
:-
<div class="row">
<div class="col-lg-12">
<div class="ibox float-e-margins">
<div class="ibox-title">
<h2>Angular 2
- User Services</h2>
</div>
<hr />
<div class="ibox-content">
<div class="table-responsive">
<table class="table table-striped">
<thead>
<tr>
<th>ID</th>
<th>Name </th>
<th>Description </th>
<th>URls </th>
</tr>
</thead>
<tbody>
<tr *ngFor="let user of users; let i =
index">
<td>{{user.id}}</td>
<td>{{user.login}}</td>
<td>{{user.description}}</td>
<td><a href="{{user.public_members_url}}"> {{user.public_members_url}}</a></td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
</div>
</div>
Result
:-
Note
–
If you need the example source code, email me and will send you code.
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