Oli Oli - 2 months ago 7
C# Question

Only Add Unique Item To List

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

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).

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