/**
         * Lays out the UINavigationItem.
         * - Parameter item: A UINavigationItem to layout.
         */
        internal void layoutNavigationItem(UINavigationItem item)
        {
            if (WillLayout)
            {
                prepareItem(item);
                prepareTitleView(item);

                var frame = item.TitleView.Frame;
                frame.Location       = CGPoint.Empty;
                frame.Size           = IntrinsicContentSize;
                item.TitleView.Frame = frame;

                var lc      = 0;
                var rc      = 0;
                var l       = ((nfloat)(item.LeftViews().Count) * InterimSpace);
                var r       = ((nfloat)(item.RightViews().Count) * InterimSpace);
                var p       = this.Width() - l - r - ContentEdgeInsets.Left - ContentEdgeInsets.Right;
                var columns = (int)(NMath.Ceiling(p / GridFactor));

                item.TitleView.Grid().Begin();
                item.TitleView.Grid().Views.Clear();
                item.TitleView.Grid().Axis.Columns = columns;

                foreach (var v in item.LeftViews())
                {
                    if (v is UIButton)
                    {
                        ((UIButton)v).ContentEdgeInsets = UIEdgeInsets.Zero;
                        ((UIButton)v).TitleEdgeInsets   = UIEdgeInsets.Zero;
                    }

                    v.SetWidth(v.IntrinsicContentSize.Width);
                    v.SizeToFit();
                    v.Grid().Columns = ((int)NMath.Ceiling(v.Width() / GridFactor)) + 2;

                    lc += v.Grid().Columns;

                    item.TitleView.Grid().Views.Add(v);
                }

                item.TitleView.Grid().Views.Add(item.ContentView());

                foreach (var v in item.RightViews())
                {
                    if (v is UIButton)
                    {
                        ((UIButton)v).ContentEdgeInsets = UIEdgeInsets.Zero;
                        ((UIButton)v).TitleEdgeInsets   = UIEdgeInsets.Zero;
                    }

                    v.SetWidth(v.IntrinsicContentSize.Width);
                    v.SizeToFit();
                    v.Grid().Columns = ((int)NMath.Ceiling(v.Width() / GridFactor)) + 2;

                    rc += v.Grid().Columns;

                    item.TitleView.Grid().Views.Add(v);
                }

                item.ContentView().Grid().Begin();

                if (item.ContentViewAlignment() == ContentViewAlignment.Center)
                {
                    if (lc < rc)
                    {
                        item.ContentView().Grid().Columns = columns - 2 * rc;
                        item.ContentView().Grid().Offset.Columns = rc - lc;
                    }
                    else
                    {
                        item.ContentView().Grid().Columns = columns - 2 * lc;
                        item.ContentView().Grid().Offset.Columns = 0;
                        if (item.RightViews().Count > 0)
                        {
                            item.RightViews()[0].Grid().Offset.Columns = lc - rc;
                        }
                    }
                }
                else
                {
                    item.ContentView().Grid().Columns = columns - lc - rc;
                }

                item.TitleView.Grid().InterimSpace      = InterimSpace;
                item.TitleView.Grid().ContentEdgeInsets = ContentEdgeInsets;
                item.TitleView.Grid().Commit();
                item.ContentView().Grid().Commit();

                // contentView alignment.
                if (!string.IsNullOrEmpty(item.Title()))
                {
                    if (item.Titlelabel().Superview == null)
                    {
                        item.ContentView().AddSubview(item.Titlelabel());
                    }
                    item.Titlelabel().Frame = item.ContentView().Bounds;
                }
                else
                {
                    item.Titlelabel().RemoveFromSuperview();
                }

                if (!string.IsNullOrEmpty(item.Detail()))
                {
                    if (item.DetailLabel().Superview == null)
                    {
                        item.ContentView().AddSubview(item.DetailLabel());
                    }

                    if (item.Titlelabel().Superview == null)
                    {
                        item.DetailLabel().Frame = item.ContentView().Bounds;
                    }
                    else
                    {
                        item.Titlelabel().SizeToFit();
                        item.DetailLabel().SizeToFit();

                        nfloat diff = (item.ContentView().Frame.Height - item.Titlelabel().Frame.Height - item.DetailLabel().Frame.Height) / 2;

                        item.Titlelabel().SetHeight(item.Titlelabel().Height() + diff);
                        item.Titlelabel().SetWidth(item.ContentView().Width());

                        item.DetailLabel().SetHeight(item.DetailLabel().Height() + diff);
                        item.DetailLabel().SetWidth(item.ContentView().Width());
                        item.DetailLabel().SetY(item.Titlelabel().Height());
                    }
                }
                else
                {
                    item.DetailLabel().RemoveFromSuperview();
                }
            }
        }