IOS下tabbar默认样式个人感觉已经很完美了，但有时候架不住奇葩的设计需求，需要进行一些更改.
1、标题字体大小
//字体设置var textAttributes = new UITextAttributes();textAttributes.Font = UIFont.FromName("ChalkboardSE-Bold", 18.0F);textAttributes.TextColor = UIColor.Black;UITabBarItem.Appearance.SetTitleTextAttributes(textAttributes, UIControlState.Normal);2、图标隐藏
//标题位置偏移，填补icon空白UITabBarItem.Appearance.TitlePositionAdjustment = new UIOffset(0, -10);3、选中项背景色设置
//tab个数，用以计算每个item的长度var itemCount = ((TabbedPage)e.NewElement).Children.Count;//通过背景图片设置，翻遍了api，貌似没发现有直接设置选中项背景色的接口var selectedImage = ImageFromColor(UIColor.Clear.FromHexString("#4b6f9f", 1.0f), new CGSize(TabBar.Bounds.Width / itemCount, TabBar.Bounds.Height));TabBar.SelectionIndicatorImage = selectedImage;/// <summary>/// 画背景色/// </summary>/// <param name="color"></param>/// <param name="size"></param>/// <returns></returns>private UIImage ImageFromColor(UIColor color, CGSize size){UIGraphics.BeginImageContext(size);var context = UIGraphics.GetCurrentContext();context.SetFillColor(color.CGColor);context.FillRect(new CGRect(new CGPoint(0, 0), size));UIImage img = UIGraphics.GetImageFromCurrentImageContext();UIGraphics.EndImageContext();return img;}4、选中项字体设置
/// <summary>/// 选中项字体设置/// </summary>public override UIViewController SelectedViewController{get{var selectedTextAttributes = new UITextAttributes();selectedTextAttributes.Font = UIFont.FromName("ChalkboardSE-Bold", 18.0F);selectedTextAttributes.TextColor = UIColor.White;if (base.SelectedViewController != null){base.SelectedViewController.TabBarItem.SetTitleTextAttributes(selectedTextAttributes, UIControlState.Normal); }return base.SelectedViewController;}set{base.SelectedViewController = value;foreach (var viewController in base.ViewControllers){var normalTextAttributes = new UITextAttributes();normalTextAttributes.Font = UIFont.FromName("ChalkboardSE-Bold", 18.0F);normalTextAttributes.TextColor = UIColor.Black;viewController.TabBarItem.SetTitleTextAttributes(normalTextAttributes, UIControlState.Normal);}}}