ComboBox.Items.AddRange Performance

Question

I have a ComboBox which when I repopulate it, it seems to be quite a time consuming task. After doing some profiling I have found that the majority of the time is spent in the ComboBox.Items.AddRange(Array) method. I have included an example method below which shows how I carryout the repopulating of the ComboBox.

public void Repopulate(IList<MyType> sortedList)
{
    MyComboBox.BeginUpdate();

    try
    {
        MyComboBox.Items.Clear();
        MyComboBox.Items.AddRange(sortedList.ToArray());
    }
    finally
    {
        MyComboBox.EndUpdate();
    }
}

sortedList contains around 280 items, and there are up to 53 ComboBox's which need to be repopulated. So it can take quite some time to repopulated all these controls (approx. 700ms on a high spec machine, 8000ms on a low spec machine) which is too slow for my requirements. I tried adding the sortedList to a new IList and that took around 1ms (on my high spec machine).

I need to get the repopulating of the ComboBox so that it takes significantly less time, ideally similar times to the IList but any performance increase would be good. So far I have been unable to find any way to improve the speed of the re-population.

Does anyone have any idea's on how I can reduce the time taken to re-populate the ComboBox?

Answer 1

Your problem could be that you have enabled the combobox's Sorted property. When this is enabled and you call AddRange the combobox sorts all those items, which if your items are already sorted, is unnecessary.

To prove my point, I created two combobox's that were populated using 10,000 sorted ints and AddRange. The only difference was that one combobox had the Sorted property enabled, the other one didn't. Here are the times in milliseconds of the resulting AddRange call

notSortedCombo: 5ms
sortedCombo: 1140ms

Could this be your problem? Could you have 53 comboboxes that have the sorted property enabled?