Some days ago, the ASP.NET team announce the official preview of Blazor, the Microsoft framework for building Single Page Application. Note that in the post, they declare that Server-Side Blazor will ship as part of .NET Core 3.0, announced for second half 2019, while Client-side Blazor will ship as part of a future .NET Core release.

Upgrade to Blazor preview

To upgrade your existing Blazor apps to the new Blazor preview first make sure you’ve installed the prerequisites listed above then follow these steps:

  • Update all Microsoft.AspNetCore.Blazor.* package references to 3.0.0-preview4-19216-03 by changing the PackageReference in csproj with this: <PackageReference Include="Microsoft.AspNetCore.Blazor" Version="3.0.0-preview4-19216-03" />
  • Remove any package reference to Microsoft.AspNetCore.Components.Server
  • Remove any DotNetCliToolReference to Microsoft.AspNetCore.Blazor.Cli and replace with a package reference to Microsoft.AspNetCore.Blazor.DevServer
  • In client Blazor projects remove the <RunCommand>dotnet</RunCommand> and <RunArguments>blazor serve</RunArguments> properties
  • In client Blazor projects add the <RazorLangVersion>3.0</RazorLangVersion> property
  • Rename all _ViewImports.cshtml files to _Imports.razor
  • Rename all remaining .cshtml files to .razor
  • Rename components.webassembly.js to blazor.webassembly.js
  • Remove any use of the Microsoft.AspNetCore.Components.Services namespace and replace with Microsoft.AspNetCore.Components as required.
  • Update server projects to use endpoint routing:

Replace this:

app.UseMvc(routes =>
    routes.MapRoute(name: "default", template: "{controller}/{action}/{id?}");

With this:


app.UseEndpoints(routes =>

Run dotnet clean on the solution to clear out old Razor declarations.