/// <summary>
/// Add a worksheet to this workbook. Sheet names must be unique.
/// </summary>
/// <exception cref="ArgumentException">Thrown if a sheet with the same Name already exists</exception>
/// <param name="sheet"></param>
public void Add(Worksheet sheet)
{
// According to ECMA-376, sheet names must be unique
if (_sheets.Any(s => s.Name == sheet.Name))
{
throw new ArgumentException("This workbook already contains a sheet named " + sheet.Name);
}
_sheets.Add(sheet);
}