vba-获取某一个sheet某一列最大行

Function getLastRow(ByVal sheetName As Worksheet, ByVal columnName As String) As Long
    Dim maxRow As Long
    If Right(rptfile, 3) = "xls" Then
        maxRow = sheetName.[A65536].End(xlUp).Row
    Else
        maxRow = sheetName.[A1048576].End(xlUp).Row
    End If
    getLastRow = maxRow
End Function