WinForms Data Grid - Asynchronously load data into an unbound column

This example handles the CustomUnboundColumnData event to load data in the Quantity unbound column.

private void OnCustomUnboundColumnData(object sender, DevExpress.XtraGrid.Views.Base.CustomColumnDataEventArgs e) {
    if (e.Column.FieldName == "Quantity")
        if (e.IsGetData) {
            object val = GetSummaryValue(e);
            e.Value = val;
        }
}
private object GetSummaryValue(DevExpress.XtraGrid.Views.Base.CustomColumnDataEventArgs e) {
    if (unboundValues.ContainsKey(e.ListSourceRowIndex)) return unboundValues[e.ListSourceRowIndex];
    unboundValues.Add(e.ListSourceRowIndex, "Not Loaded");
    GetDataAsync(e.ListSourceRowIndex);
    return unboundValues[e.ListSourceRowIndex];
}

GetDataAsync asynchronously loads row data:

private void GetDataAsync(int index) {
    GetDataDelegate d = new GetDataDelegate(GetData);
    d.BeginInvoke(index, new AsyncCallback(DataLoaded), null);
}

KeyValuePair<int, object> GetData(int index) {
    int id = Convert.ToInt32(nwindDataSet.Orders[index]["OrderID"]);
    OleDbConnection connection = new OleDbConnection(connectionSting);
    connection.Open();
    string cmdText = string.Format("SELECT SUM({0}) FROM {1} WHERE {2} = {3}", "Quantity", "OrderDetails", "OrderID", id);
    OleDbCommand command = new OleDbCommand(cmdText, connection);
    object val = command.ExecuteScalar();
    Thread.Sleep(500);
    connection.Close();
    return new KeyValuePair<int, object>(index, val);
}

Files to Review

• Main.cs (VB: Main.vb)

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