Blazor HttpClient service Error on page reload

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04-10-2024

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Blazor HttpClient Service: Taming the Reload Error

Blazor's HttpClient service is a powerful tool for making API calls from your web application. However, one common issue developers encounter is an error that occurs when the page is reloaded. This error can be frustrating, especially when the application functions perfectly the first time it loads.

Scenario:

Imagine a Blazor application that displays data fetched from a backend API. The application works seamlessly initially, displaying the retrieved data. However, upon refreshing the page, a dreaded error message appears:

System.Net.Http.HttpRequestException: An error occurred while sending the request.

Code:

@page "/"

@inject HttpClient Http

@code {
  private List<Product> products;

  protected override async Task OnInitializedAsync() {
    products = await Http.GetFromJsonAsync<List<Product>>("api/products");
  }

  // Rest of the component logic
}

Why the Error?

The root cause of this error lies in the way Blazor handles HttpClient instances. The HttpClient service is scoped to the application's lifecycle. When the page is initially loaded, a new instance of HttpClient is created. Upon reloading, Blazor tries to reuse the existing instance, but it's already been disposed by the previous lifecycle. This leads to the error when attempting to make a request using the disposed instance.

Solutions:

1. Inject HttpClient in your component: Injecting the HttpClient service directly into the component ensures a new instance is created on each page load. This is the most straightforward solution and should work for simple scenarios.

@page "/"

@inject HttpClient Http

@code {
  private List<Product> products;

  protected override async Task OnInitializedAsync() {
    products = await Http.GetFromJsonAsync<List<Product>>("api/products");
  }

  // Rest of the component logic
}

2. Utilize HttpClientFactory: The HttpClientFactory offers a more robust way to manage HttpClient instances. It allows you to configure and name different clients, making it easier to handle diverse API requests.

// Register HttpClientFactory in Startup.cs
public void ConfigureServices(IServiceCollection services)
{
  services.AddHttpClient("MyApiClient", client => 
  {
    client.BaseAddress = new Uri("https://api.example.com");
  });
}

// Inject named client in your component
@inject IHttpClientFactory clientFactory

@code {
  private List<Product> products;

  protected override async Task OnInitializedAsync() {
    var client = clientFactory.CreateClient("MyApiClient");
    products = await client.GetFromJsonAsync<List<Product>>("api/products");
  }

  // Rest of the component logic
}

3. Avoid unnecessary page reloads: In some cases, the error might be triggered by unnecessary page reloads. For instance, using @page directives with dynamic routes might cause unintended reloads. Consider alternative approaches like using @component and data binding to avoid these issues.

Additional Considerations:

• Authentication and authorization: When using HttpClient with authentication, ensure that the token is properly refreshed on page reload. This might involve implementing a custom token refresh strategy or utilizing libraries like IdentityServer4.
• State management: If your application relies on state management, ensure that the state is correctly persisted and restored on page reload. This can be achieved through techniques like using local storage or a state management library like Redux.

Conclusion:

While the HttpClient service is essential for interacting with APIs in Blazor, it's important to understand how to handle the potential error that occurs on page reload. By injecting the HttpClient directly into the component, utilizing HttpClientFactory, or adjusting your application's structure, you can ensure that your API calls succeed even after a refresh.