Xamarin Experiment - SetFlags - AppTheme_Experimental - xamarin.forms

Question

I have decided to update a Xamarin Forms app to XF 4.8. I have written some AppThemeColor for the handling of dark mode. Everything worked fine in XF 4.6. Upgrading to XF 4.8 has produced an error now where I am getting the error that AppThemeColor does not exist and wondering if I have referenced all of my assemblies. Previously, there had been a problem with the the XF 4.7 and needing to opt into the experimental theme features. Ok, so I go into my App.xaml.cs class and into the App initializor and call:
Device.SetFlags(new string[] {"AppTheme_Experimental"});
No love. Ok, so I try this in the iOS and Android projects to set the flags programmatically in the FinishedLaunching and the OnCreate methods. Still no love. I continue to get the errors.
Personally, I would think that I need to do something in a project options setting to get the compiler to pick this up, but I don't see anything.
Question: How do I turn on the AppThemeColor so that it will compile properly?
TIA,
Wally

Answer 1

You could use AppThemeBinding to handling of dark mode.
<!-- Light colors -->
<Color x:Key="LightPrimaryColor">WhiteSmoke</Color>
<Color x:Key="LightSecondaryColor">Black</Color>
<!-- Dark colors -->
<Color x:Key="DarkPrimaryColor">Teal</Color>
<Color x:Key="DarkSecondaryColor">White</Color>
<Style x:Key="ButtonStyle"
TargetType="Button">
<Setter Property="BackgroundColor"
Value="{AppThemeBinding Light={StaticResource LightPrimaryColor}, Dark={StaticResource DarkPrimaryColor}}" />
<Setter Property="TextColor"
Value="{AppThemeBinding Light={StaticResource LightSecondaryColor}, Dark={StaticResource DarkSecondaryColor}}" />
</Style>
I test on Xamarin.Forms 4.8.0.1269. It works well when i add the code below in MainActivity before Forms.Init().
Forms.SetFlags("AppTheme_Experimental");
global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
LoadApplication(new App());
You could download the source file from the link below.
https://learn.microsoft.com/en-us/samples/xamarin/xamarin-forms-samples/userinterface-systemthemesdemo/