Document what's new in ASP.NET Core for .NET 9 Preview 3

[danroth27]

Description

Update the "What's new in ASP.NET Core 9.0" for .NET 9 Preview 3

@adityamandaleeka @mkArtakMSFT Please have folks comment on this issue with the desired content.

FYI: @samsp-msft @JeremyLikness @mikekistler @claudiaregio @JamesNK @SteveSandersonMS @davidfowl

Page URL

https://learn.microsoft.com/en-us/aspnet/core/release-notes/aspnetcore-9.0?view=aspnetcore-8.0

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/release-notes/aspnetcore-9.0.md

Document ID

4e75ad25-2c3f-b28e-6a91-ac79a9c683b6

Article author

@Rick-Anderson

[JamesNK]

Endpoint metadata on the developer exception page

The attributes you add to MVC actions, Minimal APIs and gRPC methods are examples of endpoint metadata. ASP.NET Core uses endpoint metadata to control endpoint behavior, such as routing, authentication and authorization, response caching, rate limiting, OpenAPI generation and much more.

.NET 9 adds metadata to the developer exception page. You can find the new metadata information in the Routing section alongside other routing information. This is a small quality-of-life improvement to debugging ASP.NET Core errors during development.

Thank you @Kahbazi for this contribution!

[danroth27]

Handle keyboard composition events in Blazor

The new KeyboardEventArgs.IsComposing property indicates if the keyboard event is part of a composition session. This is useful for tracking the composition state of keyboard events, which is crucial for handling international character input methods.

Thank you @BattlefieldDuck for this contribution!

[danroth27]

Added InternalServerError and InternalServerError<TValue> to TypedResults

TypedResults are a helpful vehicle for returning strongly-typed HTTP status code-based responses from a minimal API. The TypedResults class now includes factory methods and types for returning "500 Internal Server Error" responses from your endpoints.

var app = WebApplication.Create();

app.MapGet("/", () => TypedResults.InternalServerError("Something went wrong!"));

app.Run();

Thank you @onurmicoogullari for this contribution!

[danroth27]

@tdykstra Looks like most of this stuff got added to the What's New doc for .NET 9, but we're still missing Handle keyboard composition events in Blazor. Can we get that added?

[guardrex]

👀

I'll put an 👁️ on this in case something else comes up. I didn't see the post.

[danroth27]

I'll put an 👁️ on this in case something else comes up. I didn't see the post.

@guardrex There's no blog post for most .NET 9 preview releases this time around. Instead, the related content is being published as release notes and then the release is announced using GitHub Discussions. Here's the release notes for ASP.NET Core in .NET 9 Preview 3: https://github.com/dotnet/core/blob/main/release-notes/9.0/preview/preview3/aspnetcore.md.