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 @pstrjds links to below (or here) to define the equality operator or you'll need to implement the equality methods in RemoteDevice (GetHashCode & Equals).