Our next example of a real-time application is a shared whiteboard. SignalR is definitely a good platform to build real-time collaborative tools, because its ability to push information to the clients makes managing a shared status easy, allowing us to keep it synchronized across several instances of the same gadget. Our whiteboard will allow users to join it and draw simple rectangles, which will be broadcasted live to all users. It will also allow us to store them on the server to keep a live history that will be used to generate the current status of the whiteboard to be pushed to new users when they connect. To build these capabilities, we'll use the following SignalR features:
Calling methods on a hub from the client
Triggering client-side callbacks from the server
Using the Groups API
Using the state bag
Handling server-side errors