如何在Xamarin PCL中更改选项卡式页面的字体大小

Question

我正在使用如下所示的选项卡式页面。请提出更改字体大小的建议。

navigationPage = new NavigationPage(new LightChannelPage(InstancePage.ActiveZone)); 
// navigationPage.Icon = Settings.IconTypeSetting.ToLower() == "monochrome" ? "Lighting.png" : "LightingClr.png"; 
if ((sarActive.Lighting != null) && (sarActive.RGB != null))     
    navigationPage.Title = "LIGHT/RGB"; 
else if (sarActive.Lighting != null)
 navigationPage.Title = "LIGHT";
 else 
    navigationPage.Title = "RGB"; 
    navigationPage.BarBackgroundColor = Color.FromHex(Settings.PrimaryColorSetting); 
    navigationPage.BarTextColor = Color.FromHex(Settings.PrimaryFontColorSetting);
    Children.Add(navigationPage);

下面是我的XAML页面代码

<?xml version="1.0" encoding="utf-8" ?>

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms" 
            xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
            xmlns:local="clr-namespace:IOTPortable.Helpers;assembly=IOTPortable.Helpers" 
            x:Class="IOTPortable.AllControllerPage" >
</TabbedPage>