不懂你想干什么。
只想一次的话:
Dim dlg As New OpenFileDialog '定义一个新的OpenFileDialog
dlg.Filter="|*.*"
If dlg.ShowDialog = DialogResult.Ok Then '如果用户单击了确定按钮
Dim mg As New Merger
mg.SourcePath = dlg.FileName
For Each dt As DataTable In DataTables
output.show(dt.name)
'For Each dc As DataCol In dt.DataCols
'output.show(dc.name)
'Next
mg.SourceTableName = dt.name
mg.DataTableName = dt.name
mg.Merge()
Exit For
Next
End If