Only Add Unique Item To List

Question

I'm adding remote devices to a list as they announce themselves across the network. I only want to add the device to the list if it hasn't previously been added.

The announcements are coming across an async socket listener so the code to add a device can be run on multiple threads. I'm not sure what I'm doing wrong but no mater what I try I end up with duplications. Here is what I currently have.....

lock (_remoteDevicesLock)
{
    RemoteDevice rDevice = (from d in _remoteDevices
                            where d.UUID.Trim().Equals(notifyMessage.UUID.Trim(), StringComparison.OrdinalIgnoreCase)
                            select d).FirstOrDefault();
     if (rDevice != null)
     {
         //Update Device.....
     }
     else
     {
         //Create A New Remote Device
         rDevice = new RemoteDevice(notifyMessage.UUID);
         _remoteDevices.Add(rDevice);
     }
}

Answer 1

If your requirements are to have no duplicates, you should be using a HashSet.

HashSet.Add will return false when the item already exists (if that even matters to you).

You can use the constructor that pstrjd mentioned below (or here) to define the equality operator or you'll need to implement the equality methods in RemoteDevice (GetHashCode & Equals).