Visual Basic

Quote:

I have an unbound DataGridView that has its VirtualMode property set to True and Visible property set to False. I am using a dynamically created DataTable that is populated by a query via the .Fill method of a SqlDataAdpater to cache the results of the query (see below).

Dim daQuery as New SqlDataAdapter(New SqlCommand(QueryText, MySqlConn))

QueryResults = New DataTable

daQuery.Fill(QueryResults)

daQuery = Nothing

I use the Rows.Clear and Columns.Clear methods of the DataGridView to clear the DataGridView each time before the query is executed (see below).

DataGridView1.Rows.Clear

DataGridView1.Columns.Clear

After the DataTable has been filled I recreate the Colmuns in the DataGridView via a For Each loop on the Columns collection of the DataTable and I use the Columns.Add method in the DataGridView to add each column to the DataGridView (see Below).

For Each QueryCol as DataColumn in QueryResults.Columns 'DataTable with Results

DataGridView1.Add("dgc" + QueryCol.ColumnName, QueryCol.ColumnName)

Next

I then create a number of blank rows that corresponds to the number of rows in the DataTable using the Rows.Add(n) method of the DataGridView (see below).

DataGridView1.Rows.Add(QueryResults.Rows.Count)

After all this is done I then set the DataGridView Visible property to True.

I have placed code in the DataGridView CellValueNeeded event to populate the cell data as it is displayed (see below).

Private Sub DataGridView1_CellValueNeeded(ByVal sender as Object, ByVal e as DataGridViewCellValueEventArgs) Handles DataGridView1.CellValueNeeded

e.Value = QueryResults.Rows(e.RowIndex).Item(e.ColumnIndex).ToString

'QueryResults is the DataTable holding the data from the query execution

End Sub

All this works fine the first time around. However, if I execute the same query a second time the DataGridView is some how retaining the data that was in it previously. The application hangs at the point where I am adding the suppose it blank rows to the DataGridView.

Before making the DataGridView visible I have checked the first row in the DataGridView by adding a single blank row and using the Immediate Window with the following statement (see below).

? DataGridView1.Rows(0).Cells(0).Value

Instead of returning an empty string it instead has the value of the first cell on the first row of the QueryResults DataTable. This should not be the case. I have tried setting the DataGridView DataSource property equal to Nothing with the same result as above.

Can someone please help me with this issue?