private void EnforceUniqueFields(SortSpec <TSortField> spec, int replaceIndex = -1)
{
for (int i = 0; i < Count; i++)
{
if (i != replaceIndex && this[i].Field.Equals(spec.Field))
{
throw new InvalidOperationException($"Cannot insert a sort specification for field {typeof(TSortField)}.{spec.Field} because one already exists.");
}
}
}
protected override void SetItem(int index, SortSpec <TSortField> spec)
{
EnforceUniqueFields(spec, index);
base.SetItem(index, spec);
}