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| title | author | description | manager | monikerRange | ms.author | ms.custom | ms.date | ms.prod | ms.technology | ms.topic | uid |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Use hubs in ASP.NET Core SignalR | rachelappel | Learn how to use hubs in ASP.NET Core SignalR. | wpickett | >= aspnetcore-2.1 | rachelap | mvc | 05/01/2018 | aspnet-core | aspnet | article | signalr/hubs |
Use hubs in SignalR for ASP.NET Core
By Rachel Appel and Kevin Griffin
View or download sample code (how to download)
What is a SignalR hub
The SignalR Hubs API enables you to call methods on connected clients from the server. In the server code, you define methods that are called by client. In the client code, you define methods that are called from the server. SignalR takes care of everything behind the scenes that makes real-time client-to-server and server-to-client communications possible.
Configure SignalR hubs
The SignalR middleware requires some services, which are configured by calling services.AddSignalR.
[!code-csharpConfigure service]
When adding SignalR functionality to an ASP.NET Core app, setup SignalR routes by calling app.UseSignalR in the Startup.Configure method.
[!code-csharpConfigure routes to hubs]
Create and use hubs
Create a hub by declaring a class that inherits from Hub, and add public methods to it. Clients can call methods that are defined as public.
[!code-csharpCreate and use hubs]
You can specify a return type and parameters, including complex types and arrays, as you would in any C# method. SignalR handles the serialization and deserialization of complex objects and arrays in your parameters and return values.
The Clients object
Each instance of the Hub class has a property named Clients that contains the following members for communication between server and client:
| Property | Description |
|---|---|
All |
Calls a method on all connected clients |
Caller |
Calls a method on the client that invoked the hub method |
Others |
Calls a method on all connected clients except the client that invoked the method |
Additionally, Hub.Clients contains the following methods:
| Method | Description |
|---|---|
AllExcept |
Calls a method on all connected clients except for the specified connections |
Client |
Calls a method on a specific connected client |
Clients |
Calls a method on specific connected clients |
Group |
Sends a message to all connections in the specified group |
GroupExcept |
Sends a message to all connections in the specified group, except the specified connections |
Groups |
Sends a message to multiple groups of connections |
OthersInGroup |
Sends a message to a group of connections, excluding the client that invoked the hub method |
User |
Sends a message to all connections associated with a specific user |
Users |
Sends a message to all connections associated with the specified users |
Each property or method in the preceding tables returns an object with a SendAsync method. The SendAsync method allows you to supply the name and parameters of the client method to call.
Send messages to clients
To make calls to specific clients, use the properties of the Clients object. In the following example, the SendMessageToCaller method demonstrates sending a message to the connection that invoked the hub method. The SendMessageToGroups method sends a message to the groups stored in a List named groups.
[!code-csharpSend messages]
Handle events for a connection
The SignalR Hubs API provides the OnConnectedAsync and OnDisconnectedAsync virtual methods to manage and track connections. Override the OnConnectedAsync virtual method to perform actions when a client connects to the Hub, such as adding it to a group.
[!code-csharpHandle events]
Handle errors
Exceptions thrown in your hub methods are sent to the client that invoked the method. On the JavaScript client, the invoke method returns a JavaScript Promise. When the client receives an error with a handler attached to the promise using catch, it's invoked and passed as a JavaScript Error object.
[!code-javascriptError]