[Blazor] Handle Errors - misleading examples on DispatchExceptionAsync (net8)

[hakenr]

@guardrex I believe the TimerService.cs + Notifications.razor example on DispatchExceptionAsync in Handle errors - Handle caught exceptions outside of a Razor component's lifecycle section is wrong.

Following the article's guidance (and the readily available example in the blazor-samples repo and easily applicable there), the exception added to TimerService.cs is reported to the user even without adding the try-catch and DispatchExceptionAsync(ex) to OnNotify method.

• This happens due to the await Timer.Start() call in StartTimer() method, where the exception from the timer loop gets propagated to Blazor

  private async Task StartTimer()
  {
      await Timer.Start();
  }

• Changing this method to a fire-and-forget approach causes exceptions not to be reported to the user

  private void StartTimer()
  {
      _ = Timer.Start();
  }

Unfortunately, adding a try-catch block to the OnNotify() method as suggested does not effectively capture or handle exceptions, since the try block does not encompass the potential source of the exception (either directly or by capturing exceptions from the task where they occur). Incorporating this try-catch into the modified example above does not route exceptions to the previously added ErrorBoundary as expected.

I can work on creating a functional example that incorporates DispatchExceptionAsync(ex); based on the TimerService.cs and Notifications.razor if that would help. However, I'd appreciate it if you could first validate the concerns I've outlined above.

Page URL

https://learn.microsoft.com/en-us/aspnet/core/blazor/fundamentals/handle-errors?view=aspnetcore-8.0#handle-caught-exceptions-outside-of-a-razor-components-lifecycle

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/blazor/fundamentals/handle-errors.md

Document ID

66a0b1c2-c45c-98ca-9808-6f340a861c44

Article author

@guardrex

[hakenr]

@guardrex I scratched a sample demonstrating the practical use of DispatchExceptionAsync method.
For easier reading I submitted my code as draft PR to the blazor-samples repo:
https://github.com/dotnet/blazor-samples/pull/186/files?diff=split&w=1

(Please double-check the sample with the PU if you decide to use it in the doc.)

[guardrex]

BTW ... Note that issues should be opened using the Open a documentation issue link/feedback form at the bottom of the article. Use of the form adds metadata to the GitHub issue that cross-links the topic and pings us automatically. I'll add the metadata to this issue manually.

I'll take a look today to see if this is a 🦖-generated example or a PU-generated example. If furnished by the PU, we'll get their input for sure. I'll take a closer look at the issue itself Tuesday (or Wednesday if things get really crazy).