Blazor WebAssembly 3.2.0 Preview 1 release now available

Daniel Roth

Daniel

Today we released a new preview update for Blazor WebAssembly with a bunch of great new features and improvements.

Here’s what’s new in this release:

  • Version updated to 3.2
  • Simplified startup
  • Download size improvements
  • Support for .NET SignalR client

Get started

To get started with Blazor WebAssembly 3.2.0 Preview 1 install the .NET Core 3.1 SDK and then run the following command:

dotnet new -i Microsoft.AspNetCore.Blazor.Templates::3.2.0-preview1.20073.1

That’s it! You can find additional docs and samples on https://blazor.net.

Upgrade an existing project

To upgrade an existing Blazor WebAssembly app from 3.1.0 Preview 4 to 3.2.0 Preview 1:

  • Update all Microsoft.AspNetCore.Blazor.* package references to 3.2.0-preview1.20073.1.
  • In Program.cs in the Blazor WebAssembly client project replace BlazorWebAssemblyHost.CreateDefaultBuilder() with WebAssemblyHostBuilder.CreateDefault().
  • Replace IWebAssemblyHost with WebAssemblyHost.
  • Replace IWebAssemblyHostBuilder with WebAssemblyHostBuilder.
  • Move the root component registrations in the Blazor WebAssembly client project from Startup.Configure to Program.cs by calling builder.RootComponents.Add<TComponent>(string selector).
  • Move the configured services in the Blazor WebAssembly client project from Startup.ConfigureServices to Program.cs by adding services to the builder.Services collection.
  • Remove Startup.cs from the Blazor WebAssembly client project.
  • If you’re hosting Blazor WebAssembly with ASP.NET Core, in your Server project replace the call to app.UseClientSideBlazorFiles<Client.Startup>(...) with app.UseClientSideBlazorFiles<Client.Program>(...).

Version updated to 3.2

In this release we updated the versions of the Blazor WebAssembly packages to 3.2 to distinguish them from the recent .NET Core 3.1 Long Term Support (LTS) release. There is no corresponding .NET Core 3.2 release – the new 3.2 version applies only to Blazor WebAssembly. Blazor WebAssembly is currently based on .NET Core 3.1, but it doesn’t inherit the .NET Core 3.1 LTS status. Instead, the initial release of Blazor WebAssembly scheduled for May of this year will be a Current release, which “are supported for three months after a subsequent Current or LTS release” as described in the .NET Core support policy. The next planned release for Blazor WebAssembly after the 3.2 release in May will be with .NET 5. This means that once .NET 5 ships you’ll need to update your Blazor WebAssembly apps to .NET 5 to stay in support.

Simplified startup

We’ve simplified the startup and hosting APIs for Blazor WebAssembly in this release. Originally the startup and hosting APIs for Blazor WebAssembly were designed to mirror the patterns used by ASP.NET Core, but not all of the concepts were relevant. The updated APIs also enable some new scenarios.

Here’s what the new startup code in Program.cs looks like:

public class Program
{
    public static async Task Main(string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        builder.RootComponents.Add<App>("app");

        await builder.Build().RunAsync();
    }
}

Blazor WebAssembly apps now support async Main methods for the app entry point.

To a create a default host builder, call WebAssemblyHostBuilder.CreateDefault(). Root components and services are configured using the builder; a separate Startup class is no longer needed.

The following example adds a WeatherService so it’s available through dependency injection (DI):

public class Program
{
    public static async Task Main(string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        builder.Services.AddSingleton<WeatherService>();
        builder.RootComponents.Add<App>("app");

        await builder.Build().RunAsync();
    }
}

Once the host is built, you can access services from the root DI scope before any components have been rendered. This can be useful if you need to run some initialization logic before anything is rendered:

public class Program
{
    public static async Task Main(string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        builder.Services.AddSingleton<WeatherService>();
        builder.RootComponents.Add<App>("app");

        var host = builder.Build();

        var weatherService = host.Services.GetRequiredService<WeatherService>();
        await weatherService.InitializeWeatherAsync();

        await host.RunAsync();
    }
}

The host also now provides a central configuration instance for the app. The configuration isn’t populated with any data by default, but you can populate it as required in your app.

public class Program
{
    public static async Task Main(string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        builder.Services.AddSingleton<WeatherService>();
        builder.RootComponents.Add<App>("app");

        var host = builder.Build();

        var weatherService = host.Services.GetRequiredService<WeatherService>();
        await weatherService.InitializeWeatherAsync(host.Configuration["WeatherServiceUrl"]);

        await host.RunAsync();
    }
}

Download size improvements

Blazor WebAssembly apps run the .NET IL linker on every build to trim unused code from the app. In previous releases only the core framework libraries were trimmed. Starting with this release the Blazor framework assemblies are trimmed as well resulting in a modest size reduction of about 100 KB transferred. As before, if you ever need to turn off linking, add the <BlazorLinkOnBuild>false</BlazorLinkOnBuild> property to your project file.

Support for the .NET SignalR client

You can now use SignalR from your Blazor WebAssembly apps using the .NET SignalR client.

To give SignalR a try from your Blazor WebAssembly app:

  1. Create an ASP.NET Core hosted Blazor WebAssembly app.

    dotnet new blazorwasm -ho -o BlazorSignalRApp
    
  2. Add the ASP.NET Core SignalR Client package to the Client project.

    cd BlazorSignalRApp
    dotnet add Client package Microsoft.AspNetCore.SignalR.Client
    
  3. In the Server project, add the following Hub/ChatHub.cs class.

    using System.Threading.Tasks;
    using Microsoft.AspNetCore.SignalR;
    
    namespace BlazorSignalRApp.Server.Hubs
    {
        public class ChatHub : Hub
        {
            public async Task SendMessage(string user, string message)
            {
                await Clients.All.SendAsync("ReceiveMessage", user, message);
            }
        }
    }
    
  4. In the Server project, add the SignalR services in the Startup.ConfigureServices method.

    services.AddSignalR();
    
  5. Also add an endpoint for the ChatHub in Startup.Configure.

    .UseEndpoints(endpoints =>
    {
        endpoints.MapDefaultControllerRoute();
        endpoints.MapHub<ChatHub>("/chatHub");
        endpoints.MapFallbackToClientSideBlazor<Client.Program>("index.html");
    });
    
  6. Update Pages/Index.razor in the Client project with the following markup.

    @using Microsoft.AspNetCore.SignalR.Client
    @page "/"
    @inject NavigationManager NavigationManager
    
    <div>
        <label for="userInput">User:</label>
        <input id="userInput" @bind="userInput" />
    </div>
    <div class="form-group">
        <label for="messageInput">Message:</label>
        <input id="messageInput" @bind="messageInput" />
    </div>
    <button @onclick="Send" disabled="@(!IsConnected)">Send Message</button>
    
    <hr />
    
    <ul id="messagesList">
        @foreach (var message in messages)
        {
            <li>@message</li>
        }
    </ul>
    
    @code {
        HubConnection hubConnection;
        List<string> messages = new List<string>();
        string userInput;
        string messageInput;
    
        protected override async Task OnInitializedAsync()
        {
            hubConnection = new HubConnectionBuilder()
                .WithUrl(NavigationManager.ToAbsoluteUri("/chatHub"))
                .Build();
    
            hubConnection.On<string, string>("ReceiveMessage", (user, message) =>
            {
                var encodedMsg = user + " says " + message;
                messages.Add(encodedMsg);
                StateHasChanged();
            });
    
            await hubConnection.StartAsync();
        }
    
        Task Send() => hubConnection.SendAsync("SendMessage", userInput, messageInput);
    
        public bool IsConnected => hubConnection.State == HubConnectionState.Connected;
    }
    
  7. Build and run the Server project

    cd Server
    dotnet run
    
  8. Open the app in two separate browser tabs to chat in real time over SignalR.

Known issues

Below is the list of known issues with this release that will get addressed in a future update.

  • Running a new ASP.NET Core hosted Blazor WebAssembly app from the command-line results in the warning: CSC : warning CS8034: Unable to load Analyzer assembly C:\Users\user\.nuget\packages\microsoft.aspnetcore.components.analyzers\3.1.0\analyzers\dotnet\cs\Microsoft.AspNetCore.Components.Analyzers.dll : Assembly with same name is already loaded.

    • Workaround: This warning can be ignored or suppressed using the <DisableImplicitComponentsAnalyzers>true</DisableImplicitComponentsAnalyzers> MSBuild property.

Feedback

We hope you enjoy the new features in this preview release of Blazor WebAssembly! Please let us know what you think by filing issues on GitHub.

Thanks for trying out Blazor!

106 comments

Comments are closed.

  • Mitchell Currey
    Mitchell Currey

    Thanks for the detailed post!

    I just have one question..
    I am attempting to apply auth to the SignalR requests, but when setting up my connection hub in the Client by using the AccessTokenProvider (as documented here), the access token I am adding is not being sent in the query params as would be expected.

    Is this a bug, or is there something I am missing that is required in Blazor by following this documentation?

    Thanks again!

  • Avatar
    Daniel Matthews

    Is it safe to say that this preview is more aligned with how the release will look when pushed in the May release? Are there going to be any other major breaking changes coming down the pipeline?

    • Daniel Roth
      Daniel RothMicrosoft logo

      We’re still listening to feedback and making changes accordingly, so yes, it’s still possible that there will be breaking changes while Blazor WebAssembly is in preview. Note that these changes are limited to Blazor WebAssembly specific functionality, like the WebAssembly host. The component model shipped already with .NET Core 3.1 and is shared with Blazor Server, so it has a very high compatibility guarantee at this point.

  • Avatar
    ysmoradi

    How can I use Autofac.Extensions.DependencyInjection in blazor 3.2? My approach was working fine with older releases, but now there is no doc to show me what to do. Thanks in advance.

  • Avatar
    Guillaume ZAHRA

    Sorry if this is duplicate, but i didn’t find any answer to this question here, and even by reading aspnet issues on GitHub, nor the documentation:

    Does the new Microsoft.AspNetCore.SignalR.Client package support connections to a regular WebSocket server (not managed by a SignalR server hub) ?
    I knew there was some limitations some times ago about using Websockets API on Blazor WASM.

    Does Microsoft.AspNetCore.SignalR.Client issue this requirement ? Otherwise, what is the alternative ? Does this kind of scenario is still impossible from C# in Blazor WASM ?

    I would like to refactor any C# to Javascript code on my project for Websocket usage.

    Regards,
    Guillaume

  • Avatar
    Steven Cramer

    Thanks again Dan,

    A few other upgrade things. Mostly occurring in test projects if you are using WebApplicationFactory.

    Replace IWebAssemblyHost with WebAssemblyHost.
    BlazorWebAssemblyHost becomes WebAssemblyHostBuilder
    Replace IWebAssemblyHostBuilder with WebAssemblyHostBuilder.

    Example of some of the changes I made in my TestFixture.

        private readonly IWebAssemblyHostBuilder WebAssemblyHostBuilder;
    
        public TestFixture(WebApplicationFactory<Server.Startup> aWebApplicationFactory)
        {
          WebApplicationFactory = aWebApplicationFactory;
          WebAssemblyHostBuilder = BlazorWebAssemblyHost.CreateDefaultBuilder()
              .ConfigureServices(ConfigureServices);
        }
    

    updated to

        private readonly WebAssemblyHostBuilder WebAssemblyHostBuilder;
    
        public TestFixture(WebApplicationFactory<Server.Startup> aWebApplicationFactory)
        {
          WebApplicationFactory = aWebApplicationFactory;
          WebAssemblyHostBuilder = WebAssemblyHostBuilder.CreateDefault();
          ConfigureServices(WebAssemblyHostBuilder.Services);
        }
    
  • Hasse Jansson
    Hasse Jansson

    Hi Daniel and all other!

    Nice work with blazor, awesome!

    I added this chathub to my app and deployed to azure, but the chat page is crashing. It works locally..

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    l.printErr @ blazor.webassembly.js:1
    put_char @ dotnet.js:1
    write @ dotnet.js:1
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    (anonymous) @ dotnet.wasm:1
    (anonymous) @ dotnet.wasm:1
    (anonymous) @ dotnet.wasm:1
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    Module._mono_wasm_invoke_method @ dotnet.js:1
    call_method @ dotnet.js:1
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    l.printErr @ blazor.webassembly.js:1
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  • Avatar
    Steven Cramer

    Hi Dan,

    dotnet –list-sdk
    3.1.101 [C:\Program Files\dotnet\sdk]
    3.1.200-preview-014883 [C:\Program Files\dotnet\sdk]

    How do I get 3.1.200-preview-014883 version of the sdk on a Linux machine? I can’t find the download link. I think VS Preview installed for me on Windows.

    Thanks.