public void SelectNext(Control selected, bool up)
{
controls = controls.OrderBy(c => c.TabIndex).ToList();
int direction = up ? 1 : -1;
int index = selected == null ? 0 : controls.IndexOf(selected);
do
{
index = (index + direction + controls.Count) % controls.Count;
}
while (controls[index].Selectable);
var newselect = controls[index];
newselect.Select();
selected.Deselect();
}