Drop AppTheme flag

[StephaneDelcroix]

Description of Change

Drop the AppTheme Flag

Issues Resolved

none

API Changes

None

Platforms Affected

• Core/XAML (all platforms)
• iOS
• Android
• UWP

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[samhouts]

@StephaneDelcroix Can you please resolve the conflicts? Thanks!

[mikebikerider]

Xamarin.Forms 4.8.0.1269 does not correctly render the iOS status bar area in Dark mode. In the dark mode the status bar area background remains white, while text color switches from black to white (as expected).
Expected behavior for the dark mode is black status bar area background. The issue is easily reproduced with a one page single grid with a 'Welcome to Xamarin Forms!' label. The page content changes correctly via AppThemeBinding applied to the grid background and the Label text color.

That problem did not exist in Xamarin Forms 4.7 builds with AppTheme_Experimental flag.
Android apps are not affected.

[vniehues]

This right here might be needed for it to work properly:

//Dark mode
UIApplication.SharedApplication.SetStatusBarStyle(UIStatusBarStyle.LightContent, true);

//Light mode
UIApplication.SharedApplication.SetStatusBarStyle(UIStatusBarStyle.DarkContent, true);

[mikebikerider]

Thank you for the suggestion, but it is not a solution.

I slightly modified the test app to better illustrate the issue.

XAML code of a test page producing the screenshot to follow:

The page has a grid with no background set. One column, three rows. The middle row holds a BoxView and a Label to show the selected Theme and the Xamarin.Forms version.
The issue affects iOS only. I deliberately did not apply UseSafeArea.

Grid rows 0 and 2 are rendered on the white background while the selected Theme is Dark. The status bar text is not visible because the status bar TextColor is White, as it should be in the Dark mode.

Xamarin Forms 4.7 and prior do render page background according to the current Theme.
Xamarin.Forms 4.8.0.1269 renders page background White regardless of the selected Theme.

A simple but silly looking 'solution' is to put following line into the ContentPage XAML section:
BackgroundColor="{AppThemeBinding Light=White, Dark=Black}"

The below XAML code will produce a correctly rendered page:

I don't recall ever applying the background to the whole page. Prior to Xamarin.Forms 4.8 there was no need for this.

Looking closely at the recently updated Xamarin documentation https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/theming/system-theme-changes August 6, 2020:
Xamarin.Forms 4.6.0.967 or greater...
I don't think code snippets offered there will produce iOS dark mode screenshots as shown if rebuilt with Xamarin.Forms 4.8.

I see benefit in setting the Page themed background in XAML. It provides clear WYSISWYG control of the iOS status bar area appearance.
My expectation is if the Page background is not set explicitly in XAML or code the page should load with the background matching the selected theme as it was in 4.6 and 4.7 Xamarin.Forms versions. The build 4.8.0.1269 loads a page on a device (simulator too) in the Dark mode with White background and that screws up the status bar area appearance. I think it should be corrected in a future build.

[stefanhk31]

So the problem with the background is currently making my app unusable (shot below is of a page with background color set to black on DarkMode, works fine in 4.7):

This page has text set to white when phone is in Dark Mode, so I believe it is responding to the OS Theme, but somehow not setting the background color properly.

Is there an open issue for this, or do I need to make one?

[mikebikerider]

Stefan, I can't tell from your screenshot if it is from iPhone or Android phone.
The issue I described affects iOS only. It is easily fixed in XAML by setting ContentPage BackgroundColor :
BackgroundColor="{AppThemeBinding Light=White, Dark=Black}"

Xamarin.Forms 4.7 with the experimental AppTheme flag loads Page with the background color matching the selected theme.
In August I updated two existing apps to Xamarin.Forms 4.8 and didn't even notice until the next day that the system notification area in Dark Mode is rendered white and no text visible because text is correctly rendered in white and not visible on the white background.
Easy to fix in XAML, but is inconsistent.

[stefanhk31]

Stefan, I can't tell from your screenshot if it is from iPhone or Android phone.
The issue I described affects iOS only. It is easily fixed in XAML by setting ContentPage BackgroundColor :
BackgroundColor="{AppThemeBinding Light=White, Dark=Black}"

Xamarin.Forms 4.7 with the experimental AppTheme flag loads Page with the background color matching the selected theme.
In August I updated two existing apps to Xamarin.Forms 4.8 and didn't even notice until the next day that the system notification area in Dark Mode is rendered white and no text visible because text is correctly rendered in white and not visible on the white background.
Easy to fix in XAML, but is inconsistent.

Sorry, should have clarified. The screenshot above is on iOS. I set the code in XAML exactly as you describe. Background appears as black with the flag on 4.7, but the white screen shows when upgrading to 4.8.

I can give specific more specific code when I'm at my workstation next, but the issue only appeared after I upgraded to 4.8.