public void RemoveListener(IDiscoveryManagerListener listener)
 {
     discoveryListeners.Remove(listener);
 }
 public void AddListener(IDiscoveryManagerListener listener)
 {
     // notify listener of all devices so far
     foreach (var device in compatibleDevices.Values)
     {
         listener.OnDeviceAdded(this, device);
     }
     discoveryListeners.Add(listener);
 }