VB.NET CRYSTAL REPORTS - Group by One Field Sort by Another

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VB

CrystalReports

i am converting a program from vb6 to vb.net and it related to crystal report.

there is function that allow user select sorting field and user can sort by more than one column. so user can read many records and use sorting to read it. now i use new crystal report dll which is crystal report 13 (should be most update version)

CrystalDecisions.CrystalReports.Engine(one of dll)
my question is :

in .net or vb6, program can use the method :

crystal.set_SortFields(i, strfields(i))
to set the fields which need to sort

but in new Crystal report dll, it will not work and need to use new coding...

so how can i handle the sorting in report by the report's fields?

i try some way:

Dim sortfiled As SortFields = reportdocument.DataDefinition.SortFields
reportdocument.DataDefinition.SortFields.Item(0).Field =reportdocument.Database.Tables("tmfphmstr").Fields("sex")
reportdocument.DataDefinition.SortFields.Item(0).SortDirection = CrystalDecisions.Shared.SortDirection.DescendingOrder
this will occurred others error there must be a group that matches this field... so sad now...waste whole day and do nothing...

please help, any information you need, just tell me.

note: in my .rpt, i did some grouping