Скачать или смотреть Troubleshooting Blazor Server-Side: Why Your Variable Isn't Updating After a Function Call

Discover the solution to the common issue in Blazor Server-Side where variables aren't updating due to the use of `OnAfterRenderAsync`. Learn best practices for using `async` and `await`.
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Troubleshooting Blazor Server-Side: Why Your Variable Isn't Updating After a Function Call

When developing a Blazor Server-Side application, you might encounter an issue where a variable does not update as expected after a function call. This can be especially frustrating if you're new to the Blazor framework. In this guide, we will explore a common problem regarding state management in Blazor, specifically the interaction between session storage and the rendering lifecycle.

Understanding the Problem

Imagine you have a simple Blazor page with a button that increments a counter and displays it on the screen. However, when you try to extend the functionality by fetching data using the OnAfterRenderAsync lifecycle method, your counter stops updating.

Here's a quick look at the code causing the issue:

[[See Video to Reveal this Text or Code Snippet]]

And the corresponding logic:

[[See Video to Reveal this Text or Code Snippet]]

In this example, the intention is to display a username from session storage each time the page is rendered. However, because OnAfterRenderAsync is executing without awaiting correctly, it disrupts further interactions on the page.

Why Does This Happen?

The key issue here is the use of .Result to retrieve data. When you block the asynchronous call by using .Result, it causes a deadlock situation leading to unexpected behavior. In other cases, the TestInc function, which should be incrementing the value of tutu, may end up never being executed.

The Solution

To solve this issue, we will adhere to a couple of best practices when working with asynchronous methods in Blazor. Follow these steps:

1. Always Use await

Replace the line causing the issue:

[[See Video to Reveal this Text or Code Snippet]]

With its correct asynchronous counterpart:

[[See Video to Reveal this Text or Code Snippet]]

2. Avoid Blocking Calls

Don’t use .Result or .Wait(): These methods can lead to deadlocks and block the asynchronous flow. Always use await instead.

3. Maintain an Unbroken Chain of Awaits

It is essential to have a clean chain of asynchronous calls. Treat warnings about “lacks await” or “is not awaited” as if they are errors to prevent unintended blocking behavior.

4. Testing the Update

Make sure to test the new implementation:

Run the application and click the button to check if the counter updates as expected.

Load the page and confirm that your session storage value is displayed without the need for a button click or reload.

Conclusion

By understanding the Blazor rendering lifecycle and adhering to best practices with asynchronous programming, you can effectively manage your app’s state. Remember, the secret to successful Blazor Server-Side applications lies in properly handling data fetching with async/await and ensuring your UI remains responsive.

Now that you've identified the problem and implemented the solution, you're on your way to mastering state management in Blazor. Happy coding!