Common mistakes

Common mistakes

Table 11.2 lists the mistakes that occur most often when developing SignalR applications.

Table 11.2. Common mistakes in SignalR applications

Problem	Cause	Fix
the client receives no messages and there are no errors	the name in On does not match the name in SendAsync; the handler is registered after StartAsync	a strongly typed hub, register On before StartAsync
user data "disappears" between calls	state is stored in hub fields	a singleton service with a thread-safe collection
InvalidOperationException: Cross-thread operation not valid	an On handler changes the form from a thread pool thread	the form's InvokeAsync or BeginInvoke
the client gets An unexpected error occurred invoking… without details	an ordinary exception in a hub method	HubException for errors intended for the client
the program crashes at startup	the server is unavailable, StartAsync without try/catch	handle HttpRequestException, retry
group messages stop arriving after a reconnect	the new connection is not in any groups	rejoin the groups in the Reconnected event
all clients "hang" while one method runs	a blocking call (Thread.Sleep, .Result) in the hub	asynchronous methods with await, long-running work in a background service
with MessagePack the handler is not called	the message type is not public	declare the record as public