Call REST API from ASP.NET Core Blazor


In this video we will discuss how to call and consume a REST API from ASP.NET Core Blazor application.

Can a Blazor component call REST API directly

Yes, a Blazor component can directly call a REST API. However, for separation of concerns and to keep the component code clean, it's a good practice to create a separate service that calls the REST API.

Create a service to call REST API

Add a folder with name Services to the Blazor web application project. Add the following 2 class files to this folder.

  1. IEmployeeService.cs
  2. EmployeeService.cs

IEmployeeService.cs

public interface IEmployeeService
{
    Task<IEnumerable<Employee>> GetEmployees();
}

EmployeeService.cs

  • We are using HttpClient class to call the REST API service.
  • This class is in System.Net.Http namespace.
  • HttpClient is injected into the EmployeeService using dependency injection.
  • We have not registered HttpClient service with the dependency injection container yet. We will do that in just a bit.
  • We are using httpClient.GetJsonAsync to call the REST API. This method is in Microsoft.AspNetCore.Blazor.HttpClient Nuget package. Install this package and do not forget to include the namespace Microsoft.AspNetCore.Components.
  • Pass the REST API endpoint (api/employees) to httpClient.GetJsonAsync method.
    httpClient.GetJsonAsync<Employee[]>("api/employees")‚Äč
using EmployeeManagement.Models;
using Microsoft.AspNetCore.Components;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;

namespace EmployeeManagement.Web.Services
{
    public class EmployeeService : IEmployeeService
    {
        private readonly HttpClient httpClient;

        public EmployeeService(HttpClient httpClient)
        {
            this.httpClient = httpClient;
        }

        public async Task<IEnumerable<Employee>> GetEmployees()
        {
            return await httpClient.GetJsonAsync<Employee[]>("api/employees");
        }
    }
}

Register HttpClient Services

In ConfigureServices method of the Startup class register HttpClient Services using AddHttpClient method.

public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages();
    services.AddServerSideBlazor();

    services.AddHttpClient<IEmployeeService, EmployeeService>(client =>
    {
        client.BaseAddress = new Uri("https://localhost:44379/");
    });
}

Call Service from Blazor Component

  • Finally call IEmployeeService from EmployeeList blazor component.
  • We use [Inject] attribute to inject a service into a Blazor component. We cannot use a constructor for this.
  • In the component OnInitializedAsync method, we call the EmployeeService.GetEmployees method.
  • The data (list of employees) that this method returns is then used to initialise Employees property.
  • The EmployeeList blazor component binds to this Employees property to display the list of employees.
using EmployeeManagement.Models;
using EmployeeManagement.Web.Services;
using Microsoft.AspNetCore.Components;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace EmployeeManagement.Web.Pages
{
    public class EmployeeListBase : ComponentBase
    {
        [Inject]
        public IEmployeeService EmployeeService { get; set; }

        public IEnumerable<Employee> Employees { get; set; }

        protected override async Task OnInitializedAsync()
        {
            Employees = (await EmployeeService.GetEmployees()).ToList();
        }
    }
}




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