---
title: ASP.NET Core SignalR .NET Client
author: bradygaster
description: Information about the ASP.NET Core SignalR .NET Client
monikerRange: '>= aspnetcore-2.1'
ms.author: bradyg
ms.custom: mvc
ms.date: 04/17/2019
uid: signalr/dotnet-client
---

# ASP.NET Core SignalR .NET Client

The ASP.NET Core SignalR .NET client library lets you communicate with SignalR hubs from .NET apps.

[View or download sample code](https://github.com/aspnet/AspNetCore.Docs/tree/master/aspnetcore/signalr/dotnet-client/sample) ([how to download](xref:index#how-to-download-a-sample))

The code sample in this article is a WPF app that uses the ASP.NET Core SignalR .NET client.

## Install the SignalR .NET client package

The `Microsoft.AspNetCore.SignalR.Client` package is needed for .NET clients to connect to SignalR hubs. To install the client library, run the following command in the **Package Manager Console** window:

```powershell
Install-Package Microsoft.AspNetCore.SignalR.Client
```

## Connect to a hub

To establish a connection, create a `HubConnectionBuilder` and call `Build`. The hub URL, protocol, transport type, log level, headers, and other options can be configured while building a connection. Configure any required options by inserting any of the `HubConnectionBuilder` methods into `Build`. Start the connection with `StartAsync`.

[!code-csharp[Build hub connection](dotnet-client/sample/signalrchatclient/MainWindow.xaml.cs?name=snippet_MainWindowClass&highlight=15-17,39)]

## Handle lost connection

Use the <xref:Microsoft.AspNetCore.SignalR.Client.HubConnection.Closed> event to respond to a lost connection. For example, you might want to automate reconnection.

The `Closed` event requires a delegate that returns a `Task`, which allows async code to run without using `async void`. To satisfy the delegate signature in a `Closed` event handler that runs synchronously, return `Task.CompletedTask`:

```csharp
connection.Closed += (error) => {
    // Do your close logic.
    return Task.CompletedTask;
};
```

The main reason for the async support is so you can restart the connection. Starting a connection is an async action.

In a `Closed` handler that restarts the connection, consider waiting for some random delay to prevent overloading the server, as shown in the following example:

[!code-csharp[Use Closed event handler to automate reconnection](dotnet-client/sample/signalrchatclient/MainWindow.xaml.cs?name=snippet_ClosedRestart)]

## Call hub methods from client

`InvokeAsync` calls methods on the hub. Pass the hub method name and any arguments defined in the hub method to `InvokeAsync`. SignalR is asynchronous, so use `async` and `await` when making the calls.

[!code-csharp[InvokeAsync method](dotnet-client/sample/signalrchatclient/MainWindow.xaml.cs?name=snippet_InvokeAsync)]

The `InvokeAsync` method returns a `Task` which completes when the server method returns. The return value, if any, is provided as the result of the `Task`. Any exceptions thrown by the method on the server produce a faulted `Task`. Use `await` syntax to wait for the server method to complete and `try...catch` syntax to handle errors.

The `SendAsync` method returns a `Task` which completes when the message has been sent to the server. No return value is provided since this `Task` doesn't wait until the server method completes. Any exceptions thrown on the client while sending the message produce a faulted `Task`. Use `await` and `try...catch` syntax to handle send errors.

> [!NOTE]
> If you're using Azure SignalR Service in *Serverless mode*, you cannot call hub methods from a client. For more information, see the [SignalR Service documentation](/azure/azure-signalr/signalr-concept-serverless-development-config).

## Call client methods from hub

Define methods the hub calls using `connection.On` after building, but before starting the connection.

[!code-csharp[Define client methods](dotnet-client/sample/signalrchatclient/MainWindow.xaml.cs?name=snippet_ConnectionOn)]

The preceding code in `connection.On` runs when server-side code calls it using the `SendAsync` method.

[!code-csharp[Call client method](dotnet-client/sample/signalrchat/hubs/chathub.cs?name=snippet_SendMessage)]

## Error handling and logging

Handle errors with a try-catch statement. Inspect the `Exception` object to determine the proper action to take after an error occurs.

[!code-csharp[Logging](dotnet-client/sample/signalrchatclient/MainWindow.xaml.cs?name=snippet_ErrorHandling)]

## Additional resources

* [Hubs](xref:signalr/hubs)
* [JavaScript client](xref:signalr/javascript-client)
* [Publish to Azure](xref:signalr/publish-to-azure-web-app)
* [Azure SignalR Service serverless documentation](/azure/azure-signalr/signalr-concept-serverless-development-config)