Async and Await in Blazor: What It Is and How to Use It

If you're building apps with Blazor, you're probably enjoying the fact that you can write C# across the stack.

But as your application gets more complex, you’ll start running into things like API calls, file uploads, or user prompts that take time to complete. If you don’t handle those interactions properly, your UI can freeze or feel unresponsive.

That’s where async and await come in.

In this post, I’ll explain what these keywords actually do in Blazor, when to use them, and how they come into play when you're modernizing legacy applications.

What Do async and await Actually Do?

Here’s a quick breakdown.

• async marks a method as asynchronous. This lets your app know that the method might take a while to finish, and it shouldn’t block the main thread while it waits.
  
  
• await is used inside an async method. It tells your app to pause execution at that point until the task is done, but without locking up the UI.

Using asynchronous methods keeps your UI responsive while background tasks finish. It helps prevent the kind of lag that makes users think your app isn’t working.

This especially matters in Blazor when the UI runs on a single thread. If you block it, everything stops responding. So if you're calling an API or showing a modal, you want to do that in a way that keeps the UI smooth and responsive.

Where You'll Use async and await in Blazor

1. On Component Initialization

Blazor gives you OnInitializedAsync(), which is useful for things like loading data from an API when a component starts. It works just like OnInitialized(), but it's built for asynchronous work.

protected override async Task OnInitializedAsync()

{

    products = await Http.GetFromJsonAsync<List<Product>>("/api/products");

}

2. In Event Handlers

If a user clicks a button and you need to fetch data or perform an action that takes time, you can use an async method. In this case, it's fine to use async void since Blazor's event system expects it, but it’s still better to return Task whenever possible for better error handling.

3. When You Need a Delay

Let’s say you want to add a loading animation or simulate waiting for a result. Task.Delay() is your friend. Just make sure the rest of your code doesn’t assume everything finishes instantly.

A Few Tips for Working with Async in Blazor

1. Use async Task instead of async void, unless you're writing an event handler like a button click.
   
   
2. You usually don't need to call StateHasChanged() after an await. Blazor handles that for you.
   
   
3. You can chain multiple await calls, and the code will run top to bottom in a readable way, much cleaner than nested callbacks.
   
   

How do the features work in our Blazor migration conversions?

In our Blazor AI migration tool, we ensure that legacy UI interactions like message boxes are properly translated into Blazor’s async/await model. 

For example, a message box that waits for user input is automatically converted to an await Message.Show(...) call, preserving the original logic and flow of the app. For this reason, it is necessary to have an asynchronous architecture for methods that call the MessageBox Show or the InputBox Show. In our tool, we are converting every awaitable call like the MessageBox into an await call.

Why This Matters

If you're modernizing an application, handling user interactions asynchronously is key. You can't block the UI the way older desktop apps did, so adopting async patterns is necessary to maintain the same logical flow while keeping your app responsive.

Our migration tooling handles this for you by converting blocking calls into async ones, updating method signatures, and preserving your application's behavior while making it ready for the web.

Final Thoughts

Blazor gives you the power of C# in the browser, and async/await makes that experience smooth and responsive. Whether you’re loading data, waiting for user input, or uploading files, asynchronous programming is a core part of building modern web apps.

And unlike JavaScript’s callback hell, C#'s async/await syntax is clean and readable, which makes your Blazor apps easier to build and maintain.