> Hi Alessandro,
>
> I suggest that you add a special row in the lookup table that is bound to
> the DataSource property of the DataGridViewComboBoxColumn. The special row
> has a dbnull value for the field which is set as the value member.
>
> For example, the lookup table has two columns named "ID" and "Name"
> respectively. The following code adds some rows including the special row
> into the lookup table.
>
> 'define a DataTable and add two columns into it
> Dim lookup As New DataTable
> Dim col As New DataColumn("ID", GetType(Integer))
> lookup.Columns.Add(col)
> col = New DataColumn("Name")
> lookup.Columns.Add(col)
>
> 'add some rows into the DataTable
> Dim row As DataRow = lookup.NewRow
> 'this is the special row added into the lookup table
> 'I don't set the value for the first column in the row because the
> default value of a DataColumn is DBNull
> row(1) = " "
> lookup.Rows.Add(row)
>
> row = lookup.NewRow
> row(0) = 1
> row(1) = "a"
> lookup.Rows.Add(row)
>
> row(0) = 2
> row(1) = "b"
> lookup.Rows.Add(row)
>
> Note that the value of the Name field of the special row mustn't equal to
> the NullValue property of the DataGridView cell. The default value of the
> NullValue property of a DataGridView cell is an empty string "".
> Otherwise,
> when the user selects the special item, the DataGridView will set the
> value
> of the current DataGridViewCell to null, but the underlying data source
> won't accept null as a valid value, so an error occurs at this time.
>
> Hope this helps.
> If you have any question, please feel free to let me know.
>
> Sincerely,
> Linda Liu
> Microsoft Online Community Support
>
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