public static void On(this IHubProxy proxy, string methodName, Action onAction)
{
if (proxy == null)
{
throw new ArgumentNullException("proxy");
}
if (String.IsNullOrEmpty(methodName))
{
throw new ArgumentNullException("methodName");
}
var subscription = proxy.Subscription(methodName);
subscription.OnCallback = onAction ?? throw new ArgumentNullException("onAction");
}