Custom combo keeps repeating itself in DataGridView

Question

I've developed a VB app which has a datagridview with a custom combobox.  The app displays patient data one patient at a time.  There is a datagridview that shows patients' family info:  name of relative, age, and ethnicity.  "Ethnicity" is a combobox.  As subsequent patients are displayed, this combo erroneously repeats itself.  For patient #1, there is one combobox.  For patient #2, there are 2 comboboxes, patient #3 - 3 combos and so on.  There should only be one combobox per patient.

The DataGridView is unbound.  With each patient, I fill the datagridview and create a combobox for the Ethnicity.

It appears that I have to clear either the datagridview or the combobox  from memory as another patient is displayed but I'm not quite sure how to do that.  I tried:

     dgvHouseHold = Nothing

But I got a "Null Reference Error".

Do I need to clear the combobox somehow and if so, how?

---

Kris Hood

Answer 1

Hi Kris,

I'm not sure what is going on without any source code. However, if you want to use combo box in a unbound DataGridView, you can add DataGridViewComboBoxColumn .

You can add the ComboBoxColumn in the designer, right click the DataGridView, select add columns..., select DataGridViewComboBoxColumn.

If there is anything unclear, please let me know. If I misunderstand you, please kindly clarify the question.

Best Regards,

---

Bob Wu [MSFT]
MSDN Community Support | Feedback to us

Answer 2

Thanks for your reply.  If I understand you correctly, you're suggesting this approach rather adding the combobox with code.  Below is the coding I use now to add the combobox to the DataGridView.  I found it online and it seems to work fine except for the repeating issue.

            strSQL = "SELECT ClientID, PersonName as [Name of Person], Relationship, Age, HIVPositive as [HIV Positive], tblClientHousehold.RaceID " & _
                "FROM tblClientHousehold " & _
                "LEFT JOIN tlkpRace ON tblClientHousehold.RaceID = tlkpRace.RaceID WHERE ClientID = " & intClientID
            daHousehold = New SqlDataAdapter(strSQL, conn)
            daHousehold.Fill(dsHousehold, strSQL)
            MyBindingSource.DataSource = dsHousehold
            MyBindingSource.DataMember = dsHousehold.Tables(0).TableName
            ' create combobox for Race
            Dim col As New DataGridViewComboBoxColumn
            col.HeaderText = "Race"
            col.DataSource = dsRace.Tables("tlkpRace")
            col.DisplayMember = "Race"
            col.ValueMember = "RaceID"
            col.DataPropertyName = "RaceID" 'this is tblClientHousehold.RaceID
            col.FlatStyle = FlatStyle.Flat
            With dgvHousehold_Fill
                .DataSource = MyBindingSource
                .Columns.Add(col)
                .Columns(0).Visible = False
                .Columns(5).Visible = False
                .Columns(6).Width = 125
                .ColumnHeadersVisible = True
                .RowsDefaultCellStyle.BackColor = Color.WhiteSmoke
                .RowsDefaultCellStyle.ForeColor = Color.Black
                .AlternatingRowsDefaultCellStyle.BackColor = Color.Gainsboro
                .AlternatingRowsDefaultCellStyle.ForeColor = Color.Black
                .ColumnHeadersDefaultCellStyle.Font = New Font(.Font, FontStyle.Bold)
                .AllowUserToAddRows = True
                .AllowUserToDeleteRows = True
                .ReadOnly = False
            End With

This code handles the selection of items in the combobox.  Again I found this online. 

    Private Sub dgvHousehold_EditingControlShowing(sender As Object, e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles dgvHousehold.EditingControlShowing
        If dgvHousehold.CurrentCell.ColumnIndex = 6 Then
            Dim cb_Race As ComboBox = e.Control
            RemoveHandler cb_Race.SelectedIndexChanged, New EventHandler(AddressOf cb_Race_SelectedIndexChanged)
            AddHandler cb_Race.SelectedIndexChanged, AddressOf Me.cb_Race_SelectedIndexChanged
        End If
    End Sub
    Private Sub cb_Race_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
        cmbBox = DirectCast(sender, ComboBox)
        intRowSave = dgvHousehold.CurrentCell.RowIndex
    End Sub

Using the method you suggested, it sounds like I could remove the code where the combobox is added to the DataGridView.  Of course I'd have to keep the code to bind data to the combobox.  Would I need the "EditingControlShowing" and "SelectedIndexChanged" events?

---

Kris Hood

Answer 3

Hi Kris,

I got confused. In your initial post, you mentioned this is an unbound DataGridView while it is a bound DatGridView according to your code.

The code seems fine. I'm not sure what do you mean by "repainting" now?

Could you please give me a screenshot to clarify what do you mean by "repeating"?

If you can share a demo with us, it would help us understand your question more clearly. You can upload demo to SkyDrive, set it share with everyone and post the link here.

Best Regards,

---

Bob Wu [MSFT]
MSDN Community Support | Feedback to us

Answer 4

I apologize.  I'm a newbie to vb.net so I might use the wrong terminology.  Hopefully the following screenshots will explain my problem.

The first image shows the datagridview for the first patient (this patient just happens to have no data yet).  You'll notice that there is only one Race combobox (and there should only be one):

This next image shows the datagridview for the next patient.  Notice there are now 2 Race comboboxes when there should be one:

If I got to a third patient, there are 4 Race comboboxes.  With a fourth patient, there are 6 comboboxes, and so on.

It appears to me that I have to wipe out the custom combobox somehow when navigating to a new patient.  I'm not sure how to do that.

Let me know if there's any other info you need. 

Thanks....Kris

---

Kris Hood

Answer 5

Hi Kris,

I'm can't detect the issue without the code but I'm sure that this caused by code logic.

I assume that you call the posted code more than one time. If so, I suggest you clear all the column each time you before you add the column. You can clean the column by call DataGridViewColumnCollection.Clear Method.

If the issue still not solved, could you please share a demo with us?

Best Regards,

---

Bob Wu [MSFT]
MSDN Community Support | Feedback to us

Answer 6

Thanks, Bob.  I think that's all it needed.  The combobox does not repeat any more. 

---

Kris Hood

Answer 7

I'm glad the issue have been solved.

Best Regards,

---

Bob Wu [MSFT]
MSDN Community Support | Feedback to us