Question

I have a DataGridView with two DataGridViewComboBoxColumns. I want to use the selected item in the first column to trigger a re-population of the items in the second column, on a per-row basis.

Here’s the code I have so far. “addlInfoParentCat” identifies the first column, and currentRow.Cells.Item(1) is the DataGridViewComboBoxCell that I want to re-populate. ExtEventAdditionalInfoType is a type I defined that contains the string/value pairs.

Private Sub dgvAdditionalInfo_CellValueChanged(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dgvAdditionalInfo.CellValueChanged
    Dim currentCell As DataGridViewCell
    currentCell = Me.dgvAdditionalInfo.CurrentCell
    If Not currentCell Is Nothing Then
        If currentCell.OwningColumn.DataPropertyName = "addlInfoParentCat" Then
            Dim parentTypeID As Integer = currentCell.Value

            Dim currentRow As DataGridViewRow = Me.dgvAdditionalInfo.CurrentRow
            Dim subtypeCell As DataGridViewComboBoxCell = currentRow.Cells.Item(1)

            Dim theChildren As New List(Of ExtEventAdditionalInfoType)

            theChildren = Custom_ExtEventAdditionalInfoType.GetChildrenOfThisParentOrderByTypeName(parentTypeID)
            subtypeCell.DataSource = Nothing
            subtypeCell.DataSource = theChildren
            subtypeCell.DisplayMember = "ExtEventAdditionalInfoTypeDescr"
            subtypeCell.ValueMember = "ID_ExtEventAdditionalInfoType"
        End If
    End If
End Sub

Basically what I see is that the binding works great the first time around. When I select a item in the first column, it populates the items correctly in the second. I can add rows to the DataGridView and repeat the process.

The problem comes when I try to change the first-column item after the second column has already been bound. I get an endless string of dialog boxes with the following:

System.ArgumentException: DataGridViewComboBoxCell value is not valid.

Any idea why this is happening? Thanks in advance!

UPDATE CodeByMoonlight’s suggestion appears to work.

I clear the DataGridViewComboBoxCell’s value before re-binding:

....

            subtypeCell.DataSource = Nothing
            subtypeCell.Value = Nothing  'here's the change
            subtypeCell.DataSource = theChildren

....

Answer 1

Well, it looks like as soon as you remodify the first combo’s value, you’re invalidating the binding and datasource you used to populate the second combo, causing all the errors.