【VB.NET】DataGridViewの連続した内容のセルの罫線を消す

 Private Sub DataGridView1_CellPainting(sender As Object, e As DataGridViewCellPaintingEventArgs) Handles DataGridView1.CellPainting

     'CustomerIDの列番号
     Dim CoustomerIDCol = DataGridView1.Columns("CustomerID").Index

     '最終行を超える場合、スキップ
     If e.RowIndex + 1 >= G_dtOrder.Rows.Count Then Return

     'CustomerID列以外の場合、スキップ
     If e.ColumnIndex <> CoustomerIDCol Then Return

     '1つ下の値
     Dim NextVal = DataGridView1.Rows(e.RowIndex + 1).Cells(CoustomerIDCol).Value

     '1つ下の値と同じ値の場合、下の罫線を消す
     If NextVal = e.Value Then
         e.AdvancedBorderStyle.Bottom = DataGridViewAdvancedCellBorderStyle.None
         DataGridView1.Rows(e.RowIndex + 1).Cells(CoustomerIDCol).Style.ForeColor = Color.White
     End If

 End Sub

 Public G_dtOrder As New DataTable
 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

     With G_dtOrder
         .Columns.Add("CustomerID", GetType(String))
         .Columns.Add("ProductName", GetType(String))
         .Columns.Add("Count", GetType(String))
         .Rows.Add("C1", "にんじん", "10")
         .Rows.Add("C1", "きゅうり", "10")
         .Rows.Add("C1", "たまねぎ", "10")
         .Rows.Add("C2", "きゃべつ", "20")
         .Rows.Add("C2", "きゅうり", "30")
         .Rows.Add("C3", "たまねぎ", "40")
     End With

     With DataGridView1
         .DataSource = G_dtOrder
         .AllowUserToAddRows = False
     End With

 End Sub

 Private Sub DataGridView1_CellPainting(sender As Object, e As DataGridViewCellPaintingEventArgs) Handles DataGridView1.CellPainting

     If e.ColumnIndex < 0 Then Return
     Debug.WriteLine(e.RowIndex & " " & e.ColumnIndex & " " & e.AdvancedBorderStyle.Top)
     Debug.WriteLine(e.RowIndex & " " & e.ColumnIndex & " " & e.AdvancedBorderStyle.Bottom)

 End Sub