DataGridViewでグループ化表示する方法

DataGridViewでグループ化表示する方法
VB.NET

Private defaultCellStyle As DataGridViewCellStyle
Private groupCellStyle As DataGridViewCellStyle

Private Sub Form1_Load(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles MyBase.Load
    Me.defaultCellStyle = New DataGridViewCellStyle()
    Me.groupCellStyle = New DataGridViewCellStyle()
    Me.groupCellStyle.ForeColor = Color.White
    Me.groupCellStyle.BackColor = Color.DarkGreen
    Me.groupCellStyle.SelectionBackColor = Color.DarkBlue
End Sub

Private Sub dgv1_CellFormatting(ByVal sender As Object, _
        ByVal e As DataGridViewCellFormattingEventArgs) _
        Handles dgv1.CellFormatting
    Dim dgv As DataGridView = CType(sender, DataGridView)
    If e.ColumnIndex = 0 AndAlso e.RowIndex >= 0 AndAlso _
        e.RowIndex <> dgv.NewRowIndex Then
        If e.RowIndex = 0 OrElse _
            Not dgv(e.ColumnIndex, e.RowIndex - 1).Value.Equals(e.Value) Then
            dgv.Rows(e.RowIndex).DefaultCellStyle = Me.groupCellStyle
        Else
            dgv.Rows(e.RowIndex).DefaultCellStyle = Me.defaultCellStyle
            e.Value = ""
            e.FormattingApplied = True
        End If
    End If
End Sub

C#

private DataGridViewCellStyle defaultCellStyle;
private DataGridViewCellStyle groupCellStyle;

private void Form1_Load(object sender, EventArgs e)
{
    this.defaultCellStyle = new DataGridViewCellStyle();
    this.groupCellStyle = new DataGridViewCellStyle();
    this.groupCellStyle.ForeColor = Color.White;
    this.groupCellStyle.BackColor = Color.DarkGreen;
    this.groupCellStyle.SelectionBackColor = Color.DarkBlue;
}

private void dgv1_CellFormatting(object sender,
    DataGridViewCellFormattingEventArgs e)
{
    DataGridView dgv = (DataGridView)sender;
    if (e.ColumnIndex == 0 && e.RowIndex >= 0 &&
        e.RowIndex != dgv.NewRowIndex)
    {
        if (e.RowIndex == 0 ||
            !dgv[e.ColumnIndex, e.RowIndex - 1].Value.Equals(e.Value))
        {
            dgv.Rows[e.RowIndex].DefaultCellStyle = this.groupCellStyle;
        }
        else
        {
            dgv.Rows[e.RowIndex].DefaultCellStyle = this.defaultCellStyle;
            e.Value = "";
            e.FormattingApplied = true;
        }
    }
}