C#

string update_string = null;

update_string = "some text here";

updateDialog.RightToLeftLayout = true;
updateDialog.WindowTitle = "title here";
updateDialog.MainInstruction = update_string;
updateDialog.CustomMainIcon = Properties.Resources.whatwhen;

List<TaskDialogButton> updateButtons = new List<TaskDialogButton>();

TaskDialogButton btnCancel = new TaskDialogButton();
btnCancel.ButtonId = 100;
btnCancel.ButtonText = "cancel";
updateButtons.Add(btnCancel);

updateDialog.Buttons = updateButtons.ToArray();

updateDialog.ShowMarqueeProgressBar = true;

updateDialog.Footer = "please wait...";
updateDialog.FooterIcon = TaskDialogIcon.Information;

updateDialog.Callback = new TaskDialogCallback(this.TaskDialogCallback);

int update_result = updateDialog.Show();



private bool TaskDialogCallback(ActiveTaskDialog updateDialog, TaskDialogNotificationArgs args, object callbackData)
{
    if (args.Notification == TaskDialogNotification.Created)
    {
        updateDialog.SetProgressBarMarquee(true, 0);
        return false;
    }
}