private IEnumerable <TWorksheet> ReadWorksheetsWithCache()
{
// Iterate TWorkbook.ReadWorksheets() only once and cache the
// worksheet instances, which are expensive to create.
if (_cachedWorksheets != null)
{
foreach (var worksheet in _cachedWorksheets)
{
yield return(worksheet);
}
if (_cachedWorksheetIterator == null)
{
yield break;
}
}
else
{
_cachedWorksheets = new List <TWorksheet>();
}
if (_cachedWorksheetIterator == null)
{
_cachedWorksheetIterator = Workbook.ReadWorksheets().GetEnumerator();
}
while (_cachedWorksheetIterator.MoveNext())
{
_cachedWorksheets.Add(_cachedWorksheetIterator.Current);
yield return(_cachedWorksheetIterator.Current);
}
_cachedWorksheetIterator.Dispose();
_cachedWorksheetIterator = null;
}