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

        private void TrackDropDown(int index)
        {
            while (index >= 0)
            {
                this.trackNextItem = -1;

                this.BeginUpdate();

                CommandBarMenu menu = this.items[index] as CommandBarMenu;
                if (menu != null)
                {
                    menu.PerformDropDown(EventArgs.Empty);
                    this.contextMenu.Items.Clear();
                    this.contextMenu.Items.AddRange(menu.Items); // = menu.Items;
                    this.contextMenu.Mnemonics = true;
                }
                else
                {
                    this.contextMenu.Items.Clear(); // .Items = new CommandBarItemCollection();
                    this.contextMenu.Mnemonics = true;
                }

                // Item state
                NativeMethods.SendMessage(this.Handle, NativeMethods.TB_PRESSBUTTON, index, -1);

                // Trick to get the first menu item selected
                NativeMethods.PostMessage(this.Handle, NativeMethods.WM_KEYDOWN, (int) Keys.Down, 1);
                NativeMethods.PostMessage(this.Handle, NativeMethods.WM_KEYUP, (int) Keys.Down, 1);

                this.SetState(State.HotTracking, index);

                // Hook
                NativeMethods.HookProc hookProc = new NativeMethods.HookProc(DropDownHook);
                GCHandle hookProcHandle = GCHandle.Alloc(hookProc);
                this.hookHandle = NativeMethods.SetWindowsHookEx(NativeMethods.WH_MSGFILTER, hookProc, IntPtr.Zero, NativeMethods.GetCurrentThreadId());
                if (this.hookHandle == IntPtr.Zero)
                {
                    throw new SecurityException();
                }

                // Ask for position
                NativeMethods.RECT rect = new NativeMethods.RECT();
                NativeMethods.SendMessage(Handle, NativeMethods.TB_GETRECT, index, ref rect);
                Point position = new Point(rect.left, rect.bottom);

                this.EndUpdate();
                this.Update();

                this.contextMenu.Show(this, position);

                // Unhook
                NativeMethods.UnhookWindowsHookEx(hookHandle);
                hookProcHandle.Free();
                this.hookHandle = IntPtr.Zero;

                // Item state
                NativeMethods.SendMessage(Handle, NativeMethods.TB_PRESSBUTTON, index, 0);
                this.SetState(trackEscapePressed ? State.Hot : State.None, index);

                index = trackNextItem;
            }
        }