Question

(note: I have labelled this C# but I am using Monotouch, so it might behave differently, I’m not too sure)

Here is my scenario:
I have a List which persists throughout my app, this holds onto an entire list of objects. I then filter this data (via user choices in the app) and display the appropriate items.

The list gets updated by a call to the webservice, the way I do this is as follows:

HandleWebServiceComplete(object sender, ItemRetreivedEventArgs e)
{
    // snip - error handling above this

    if (e.Result != null)
    {
        foreach (var item in e.Result)
        {
            if (!mainList.Contains(item))
                mainList.Add(item);
        }

        RefreshDisplayList(mainList);
    }
}

So obviously this checks every single item returned by the web service, to check that it doesn’t already exist in the list (there are situations where it could) – so my question is, would it be better to use List.AddRange() then check for duplicates in the list afterwards or just carry on the way I’m going already?

Answer 1

I definitely would not AddRange and then remove duplicates, as each removal will trigger a rebuild of the backing array. The way you are doing it is fine. I presume you are not actually having performance issues currently.