/// <summary>
/// Subscribes for change events for all state variables of this service.
/// </summary>
/// <remarks>
/// If the event subscription fails, the delegate <see cref="EventSubscriptionFailed"/> will be called.
/// </remarks>
/// <exception cref="IllegalCallException">If the state variables are already subscribed
/// (see <see cref="IsStateVariablesSubscribed"/>).</exception>
public void SubscribeStateVariables()
{
DeviceConnection connection = _connection;
if (connection == null)
{
throw new IllegalCallException("UPnP service is not connected to a UPnP network service");
}
if (connection.IsServiceSubscribedForEvents(this))
{
throw new IllegalCallException("State variables are already subscribed");
}
connection.OnSubscribeEvents(this);
}