Bulk loading in ObservableCollection.

Today, in Code Project, a poster asked a question about the best way to insert multiple items in ObservableCollection as a bulk insert. The poster wondered why it was taking so long to add records doing an Add for each item in the collection. Now, in several of the .NET collections, there’s an AddRange method that allows you to add multiple items in “one hit”, so why isn’t there one in ObservableCollection? Well, part of the reason seems to be that this goes outside what you would use an ObservableCollection for. In other words, it’s not aimed at adding multiple items, it’s aimed at monitoring small changes.

So, what makes ObservableCollection unsuitable for large scale inserts? Well, the primary reason lies in the fact that an Add operation fires off a CollectionChanged event – it’s this event that is contributing to a large part of the slowdown. Fortunately, there is a way to get round this limitation, and it lies in the wonderful world of inheritance.

The following class is based on an ObservableCollection, and adds a new method (AddRange) that adds the items in quickly by suppressing the CollectionChanged event until the load has finished. (It doesn’t implement a RemoveRange method, but it would follow a similar pattern). Simple tests showed that this ran 3 times faster than the ordinary methods.

public class RangeObservableCollection<T> : ObservableCollection<T>
{
  private bool _suppressNotification = false;

  protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
  {
    if (!_suppressNotification)
      base.OnCollectionChanged(e);
  }

  public void AddRange(IEnumerable<T> list)
  {
    if (list == null)
      throw new ArgumentNullException("list");

    _suppressNotification = true;

    foreach (T item in list)
    {
      Add(item);
    }
    _suppressNotification = false;
    OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
  }
}

Anyway, I hope this helps you out.

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