Angular – How to consume a Web API

By | 21/08/2019

In this post, we will create an Angular application that it will show a list of users taken from the Web API created in the post: Web API with ASP.NET Core.

We open Terminal and create a new project called “manageusers”:

ng new manageusers



Now, we will create a component called listeners for showing the list of users.
We go into project directory and we run the command:

ng g c listusers



Now, we will create the class User:

ng g class user



Finally, we create the “service” called webapiuser to manage the calls from the Web API service:

ng g service webapiuser



Now, we will define all components created until now:

[USER.JS]

export class User 
{
    id: number;
    username: string;
    typeUserName: string;
    createDate: string;
}



[WEBAPIUSER.JS]

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs';
import { User } from './user';

@Injectable({
  providedIn: 'root'
})
export class webapiuser {

  // Web Api service url
  webapiUserUrl = 'https://firstwebapi001.azurewebsites.net/api';

  constructor(private http: HttpClient) { }

  // define a method  getListUsers for calling the user method of Web Api service
  getListUsers(): Observable<Array<User>> {  
    return this.http.get<Array<User>>(this.webapiUserUrl + '/user');  
  }  
}



[LISTUSERS.JS]

import { Component, OnInit } from '@angular/core';
import { User } from '../user';
import { webapiuser } from '../webapiuser.service';

@Component({
  selector: 'app-listusers',
  templateUrl: './listusers.component.html',
  styleUrls: ['./listusers.component.css']
})
export class ListusersComponent implements OnInit {
  // define an Array of User
  lstUsers: Array<User>;

  // Use the dependency injection to use the service in this component
  constructor(private serviceuser: webapiuser) { }

  ngOnInit() {
    
    // call the service to take the list of users
    this.serviceuser.getListUsers().subscribe(data => {
      this.lstUsers = data;
    });
  }
}



[LISTUSERS.COMPONENT.HTML]

<p>List of Users</p>
<table>
    <tr>
        <td>ID</td>
        <td>Username</td>
        <td>TypeUser</td>
        <td>Create Data</td>  
    </tr>
    <tbody *ngFor="let item of lstUsers"> 
        <tr>
            <td>{{item.id}}</td>
            <td>{{item.username}}</td>
            <td>{{item.typeUserName}}</td>
            <td>{{item.createDate}}</td>
        </tr>
    </tbody>
</table>



In app.component.html, we delete everything and leave only:

<router-outlet>
</router-outlet>



Now, we modify the file app-routing.module.ts:

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { ListusersComponent } from './listusers/listusers.component';


const routes: Routes = [
  { path: '', pathMatch: 'full', redirectTo: 'listusers'},
  { path: 'listusers', component: ListusersComponent },
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }



Finally, we verify that the file app.module.ts is like that:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpClientModule } from '@angular/common/http'; 

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { ListusersComponent } from './listusers/listusers.component';

@NgModule({
  declarations: [
    AppComponent,
    ListusersComponent
  ],
  imports: [
    BrowserModule,
    AppRoutingModule,
    HttpClientModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }



Now, we run the application using the command ng serve, open a browser and we go to: http://localhost:4200

We can see that the application doesn’t work.
This because, I forgot to set up the CORS in my Web Api.
Now, we can fix it either via code or using the configuration in Azure and, for this post, we will use the second choice.

We go on Azure portal, select the web app, we click CORS in API and we set up the Allowed Origins.
In this case, I will insert localhost:4200.

Now, if we try to run the application again, this will be the result:



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