a.cs

private bool IsItemsSourceEmpty() 
{
    if (DataSource == null)
        return true;

    var collection = DataSource as ICollection;
    if (collection != null)
        return collection.Count > 0;

    var enumerator = DataSource.GetEnumerator();
    var hasElement = enumerator.MoveNext();
    (enumerator as IDisposable)?.Dispose();
    return !hasElement;
}