poi合併單元格後居中

//設置style
ICellStyle cellstyle = workbook.CreateCellStyle();
cellstyle.VerticalAlignment = VerticalAlignment.Center;
cellstyle.Alignment = HorizontalAlignment.Center;

//合併操作

sheet.AddMergedRegion(new CellRangeAddress(index["firstRow"], index["lastRow"], index["firstCol"], index["lastCol"]));//起始行，結束行，起始列，結束列

//設置合併後style
var cell = sheet.GetRow(index["firstRow"]).GetCell(index["firstCol"]);
cell.CellStyle = cellstyle;