ASP.NET Core updates in .NET 5 Release Candidate 2

.NET 5 Release Candidate 2 (RC2) is now available and is ready for evaluation. .NET 5 RC2 is a “go live” release, meaning it’s supported in production. This prerelease of .NET 5 is very close to what we expect to ship for the .NET 5 release.

Here’s what’s new in this RC2 release:

CSS isolation improvements
Blazor WebAssembly debugging improvements
Browser platform compatibility tooling

ASP.NET Core in .NET 5 contains lots of great new functionality and improvements! The list below summarizes the many improvements we’ve made in ASP.NET Core for .NET 5 that you can try out in this release:

See the .NET 5 release notes for additional details and known issues.

Get started

To get started with ASP.NET Core in .NET 5 RC2, install the .NET 5 SDK. .NET RC2 also is included with Visual Studio 2019 16.8 Preview 4.

Visual Studio 2019 16.8 Preview 4 or later is required to use .NET 5 RC2 from Visual Studio. .NET 5 RC2 is also supported with the latest preview of Visual Studio for Mac. To use .NET 5 with Visual Studio Code, install the latest version of the C# extension.

Upgrade an existing project

To upgrade an existing ASP.NET Core app from .NET 5 RC1 to .NET 5 RC2:

Update all Microsoft.AspNetCore.* package references to 5.0.0-rc.2.*.
Update all Microsoft.Extensions.* package references to 5.0.0-rc.2.*.
Update System.Net.Http.Json package references to 5.0.0-rc.2.*.
Update Microsoft.AspNetCore.Components.Web.Extensions package references to 5.0.0-preview9.20513.1.
Remove any package references to Microsoft.AspNetCore.Components.ProtectedBrowserStorage
Update Microsoft.AspNetCore.Components.ProtectedBrowserStorage namespace to Microsoft.AspNetCore.Components.Server.ProtectedBrowserStorage.
Remove unnecessary service registrations for ProtectedLocalStorage and ProtectedSessionStorage.
Rename JSObjectReference to IJSObjectReference.
In Blazor apps, replace CSS references to _framework/scoped.styles.css and _content/{project_name}/_framework/scoped.styles.css with {project_name}.styles.css.

That’s it! You should be all ready to go.

See also the full list of breaking changes in ASP.NET Core for .NET 5.

What’s new?

Blazor CSS isolation improvements

In .NET 5 Preview 8 we introduced support for CSS isolation for Blazor components. Based on user feedback, we’ve made a number of improvements to CSS isolation in this release.

Previously, all component scoped CSS files including files from referenced projects or packages were compiled into a single bundle, scoped.styles.css. We now produce one bundle per referenced project or package and include those bundles into the app bundle through CSS @import statements.

The bundle names are now based on the project names: {project_name}.styles.css. Each bundle can be referenced from the root path of the app by default. This makes the path of the app bundle the same for both Blazor Server and Blazor WebAssembly projects:

<link href="BlazorApp1.styles.css" rel="stylesheet" />

Component specific styles can also now use normal wwwroot-relative paths to refer to related assets, like images. We’ve updated Razor Class Library template to make use of component specific styles following this pattern.

Component1.razor.css

.my-component {
    border: 2px dashed red;
    padding: 1em;
    margin: 1em 0;
    background-image: url('background.png');
}

We also fixed some issues with how scoped CSS styles get built so that changes are correctly picked up with each build in Visual Studio instead of requiring a full rebuild.

Blazor WebAssembly debugging improvements

.NET 5 includes a variety of improvements to Blazor WebAssembly debugging:

Various reliability improvements, including fixing the port conflict issue from RC1
Improved support for stepping over and out of async methods
Inspect locals or object properties in many previously unsupported situations:
- For inherited members
- For multicast delegates
- For boxed values
- For Nullable<T> values
- Within reflection based calls
Support for debugging lazy loaded assemblies

Browser platform compatibility tooling

The core framework libraries in .NET 5 have now been annotated to indicate which APIs are supported in browser scenarios. The platform compatibility analyzer uses this data to give appropriate warnings when using APIs from a Blazor WebAssembly app that are not supported when running in a browser on WebAssembly.

Browser compatibility check

Learn more about how you can use the new platform compatibility analyzer to discover cross-platform compatibility issues.

Give feedback

We hope you enjoy this release of ASP.NET Core in .NET 5! We are eager to hear about your experiences with this latest .NET 5 release. Let us know what you think by filing issues on GitHub.

Thanks for trying out ASP.NET Core!

56 comments

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Oliver Waits October 26, 2020

I was wondering if anyone else has been struggling with a conflict between Team Viewer and trying to debug a Blazor project. With Team Viewer installed and running it seems to consume ports required by the debugger and prevents IIS from running. You get an error saying IIS has failed to start when you press play. In Kestral it just seems to just not do anything. The fix is to end process on all Team Viewer services multiple times as it repeatedly tries to restart. Eventually it gives up and the process terminates. You can then restart visual studio and...
Read more
I was wondering if anyone else has been struggling with a conflict between Team Viewer and trying to debug a Blazor project. With Team Viewer installed and running it seems to consume ports required by the debugger and prevents IIS from running. You get an error saying IIS has failed to start when you press play. In Kestral it just seems to just not do anything. The fix is to end process on all Team Viewer services multiple times as it repeatedly tries to restart. Eventually it gives up and the process terminates. You can then restart visual studio and life is good till you reboot your machine. This is happening on multiple machines with Team Viewer. I tried changing the port used by my application but that did not seem to fix it. This only started happening after installing RC2 in RC1 it was fine.

Read less
- Safia Abdalla October 26, 2020
  
  Thanks for sharing, Oliver!
  
  Can you use the “report a problem” UI in VS to report this bug for investigation?
  
  It’s a bit counterintuitive that it works in RC2 but not RC1 since we made improvements to the way that ports are assigned to the debug proxy process.
Jung, Oliver October 21, 2020

What about OData Support?
- Daniel Roth Author October 21, 2020
  
  You can learn alll about OData support for ASP.NET Core here: https://docs.microsoft.com/en-us/odata/webapi/netcore.
Anna R October 19, 2020
Help with feature “Control Startup class activation”
->
```
 var host = Host.CreateDefaultBuilder()
            .ConfigureWebHost(builder =>
            {
                builder.UseStartup(context => new Startup(logger));
            })
            .Build();
```
When I use Project Sdk=”Microsoft.NET.Sdk.BlazorWebAssembly”, I get error: ‘IHostBuilder’ does not contain a definition for ‘ConfigureWebHostDefaults’
When I set Project Sdk=”Microsoft.NET.Sdk.Web”, project see ConfigureWebHostDefaults, but project doesn’t work….
- Daniel Roth Author October 19, 2020
  
  Hi Anna. The feature to control Startup class activation is specific to ASP.NET Core projects, which use the MIcrosoft.NET.Sdk.Web SDK. This is not a feature that can be used from Blazor WebAssembly projects.
Darrell Tunnell October 19, 2020

Missed an update step, –> update global.json from sdk version 5.0.100-rc.1.20452.10 to 5.0.100-rc.2.20479.15