System.Windows.Forms.CommandBar.GetPreviousItem C# (CSharp) Method

        private int GetPreviousItem(int index)
        {
            if (index < 0)
            {
                throw new ArgumentException("index");
            }

            int count = NativeMethods.SendMessage(this.Handle, NativeMethods.TB_BUTTONCOUNT, 0, 0);

            int prevIndex = index;
            do
            {
                prevIndex = (prevIndex + count - 1) % count;
            }
            while ((prevIndex != index) && (!items[prevIndex].IsVisible));

            return prevIndex;
        }