DataGridview Problem add combobox column

[danasegarane]

Dear All,
Now I have code this to display the combo box in a datagrid.But I am not able to edit the combo values.How can I add the entered values in the combobox to the item collection.I am using this code

         ngrid = New DataGridView
                 ngrid.Name = sname
                 nGrid.Visible = True
                 ngrid.Location = New Point(275, 32)
                 ngrid.Width = 244
                 ngrid.Height = 160
                 AddHandler nGrid.Click, AddressOf ngrid_Click
                 Me.Controls.Add(nGrid)
                 nGrid.Rows.Clear()
                If dtCombo.Rows.Count > 0 Then
                    nGrid.EditMode = DataGridViewEditMode.EditOnEnter
                    nGrid.AutoGenerateColumns = False
                    nGrid.Columns.Add("col0", "Attribute")
                    nGrid.Columns.Add("col1", "Value")
                    For x As Long = 0 To dtCombo.Rows.Count - 1
                        Dim xedit As String = String.Empty
                        Dim i As Integer = nGrid.Rows.Add
                        xedit = nz((dtCombo.Rows(x)(3)).ToString)
                        Dim cmbcombocol As New DataGridViewComboBoxCell
                        cmbcombocol.Items.AddRange((dtCombo.Rows(x)(2)).ToString.Split(";"))
                        Dim atxt As New DataGridViewTextBoxCell
                        atxt.Value = nz((dtCombo.Rows(x)(1)).ToString)
                        ngrid.Rows(i).Cells(0) = atxt
                        nGrid.Rows(i).Cells(1) = cmbcombocol
                        ngrid.Columns(0).ReadOnly = True
                        If xedit.ToString.ToLower = "y" Then
                            cmbcombocol.ReadOnly = False
         
                        Else
                            cmbcombocol.ReadOnly = False
                        End If
                    Next
                End If