vb.net给DataGridView添加全选功能

 Private Sub AddSelectAllCheckBox(ByVal dgv As DataGridView)
        Dim cbx As New CheckBox
        cbx.Name = "SelectAll"
        cbx.Size = New Size(14, 14)

        Dim rect As Rectangle
        rect = dgv.GetCellDisplayRectangle(0, -1, True)
        cbx.Location = New System.Drawing.Point(rect.Location.X + ((rect.Width - cbx.Width) / 2), rect.Location.Y + ((rect.Height - cbx.Height) / 2))
        dgv.Controls.Add(cbx)

        AddHandler cbx.Click, AddressOf HeaderCheckBox_Click
    End Sub

    Private Sub HeaderCheckBox_Click(ByVal sender As Object, ByVal e As EventArgs)
        If DataGridView_Discre.Rows.Count > 0 Then
            Dim cbx As CheckBox
        &n