.NET Framework应用对接Flutter SignalR的解决方案咨询

Hey there, let's tackle your two related .NET and SignalR questions with practical, actionable solutions:

Directly referencing a .NET Core class library from a .NET Framework project isn't straightforward due to framework compatibility differences, but you have two reliable workarounds:

• Use a .NET Standard Class Library as a Middle Layer
  .NET Standard is a cross-framework specification supported by .NET Framework 4.6.1+ and all .NET Core/.NET 5+ versions. Migrate the code from your .NET Core class library into a .NET Standard class library, then reference this standard library in your .NET Framework project. This enables seamless code sharing across both frameworks.
• Package the .NET Core Library as a NuGet Package
  If you need to keep the .NET Core library intact, pack it into a NuGet package. Ensure your .NET Framework project uses version 4.6.1 or higher (to meet the package's dependency requirements), then install the NuGet package directly into the .NET Framework project.

The core issue here is that traditional ASP.NET SignalR (for .NET Framework) uses a different protocol than ASP.NET Core SignalR, which is the version supported by Flutter's official signalr_core client. Here are the best ways to resolve this:

Option 1: Build an ASP.NET Core SignalR Relay Service (Most Recommended) #

Set up a lightweight ASP.NET Core SignalR service to act as a middleman between your existing .NET Framework SignalR app and Flutter clients:

• Create a new ASP.NET Core project and add the ASP.NET Core SignalR package.
• Implement a relay hub that connects to your .NET Framework SignalR app (using the .NET Framework SignalR client) and forwards messages between the two systems:

  public class SignalRRelayHub : Hub
  {
      private readonly IHubConnection _dotNetFrameworkHubConnection;
  
      public SignalRRelayHub(IHubConnection dotNetFrameworkHubConnection)
      {
          _dotNetFrameworkHubConnection = dotNetFrameworkHubConnection;
          // Listen for messages from .NET Framework and broadcast to Flutter
          _dotNetFrameworkHubConnection.On<string>("ReceiveMessage", async message => 
              await Clients.All.SendAsync("ReceiveMessage", message));
      }
  
      // Receive messages from Flutter and send to .NET Framework
      public async Task SendToDotNetFramework(string message)
      {
          await _dotNetFrameworkHubConnection.SendAsync("SendMessage", message);
      }
  }
  

• Provide Flutter clients with the URL of this ASP.NET Core SignalR service, and use the signalr_core Dart package to establish connections.

Option 2: Upgrade Your .NET Framework App to .NET (Core) #

If your project's dependencies allow, upgrading to .NET 6/7/8 lets you replace traditional ASP.NET SignalR with ASP.NET Core SignalR natively:

• Use Visual Studio's .NET Upgrade Assistant to automate most of the migration process.
• Update your SignalR hubs and server configuration to use ASP.NET Core SignalR.
• Once upgraded, you can directly share the ASP.NET Core SignalR URL with Flutter clients, no relay needed.

Option 3: Third-Party Compatibility Libraries (Not Recommended) #

There are unofficial Dart packages that claim to support traditional ASP.NET SignalR, but these often lack active maintenance and may have stability or compatibility issues. This should only be a temporary workaround if the above options aren't feasible right now.

内容的提问来源于stack exchange，提问作者Do Sok Ho