Theme Selector

Provides a workaround to address the Maui RequestedThemeChanged problem on android.

See dotnet/maui#8236: Application.Current.RequestedThemeChanged event only raises once

The workaround involves an android-specific class, ThemeInfo, that reads the underlying Configuration.UiMode theme value and a CheckTheme() method to periodically check to see if the theme has changed and raising an RequestedThemChanged event. In the example, ThemeInfo.CheckTheme() is by MainActivity.cs.

Note MauiAppCompatActivity.OnConfigurationChanged is not getting called so I could not use that as polling model.

Classes

• Platforms/Android/ThemeInfo.cs

  The Theme property reads the theme from the native Configuration.UiMode. CheckTheme() determines if the native theme has changed. If not, it raises it's RequestedThemeChanged event.

• Platforms/Android/MainActivity.cs

  Android SDK 30 or greater

  Overrides OnConfigurationChanged and calls ThemeInfo.CheckThem.

  Android SDK < 30

  Overrides OnWindowFocusChanged and calls ThemeInfo.CheckTheme() when hasFocus = true. This is not ideal since the application doesn't see the theme change until it next receives focus; however, it avoids polling the system theme.

• App.cs

  Provides a mirror to the RequestedTheme property via SystemTheme and the RequestedThemeChanged event via SystemThemeChanged. It uses Platforms/Android/ThemeInfo. on Android, and Application.Current.RequestedTheme on all other platforms.

• MainViewModel.cs

  Illustrates using the mirror APIs to adjust the application's theme.

• MainPage.xaml

  Provides a set of radio buttons to test switching between Dark, Light, and System (AppTheme.Unspecified) themes.

SDK Note:

At the time of this writing, the Maui application template targets Android 5/21. This impacts the application in two ways:

1: OnWindowFocusChanged(true) is used to poll for theme changes. Using SDK 30 solves this.

2: RadioButton theme support does not render correctly when using DynamicResource to set text and background colors. SDK 30 definitely solves this but earlier targets may as well.

RadioButton and custom Themes:

I'm finding RadioButton to be problematic when used with themes as illustrated in below issues.

The MainPage displays two sets of RadioButtons.

1: The first group uses the MAUI RadioButton defines a style to set the RadioButton's TextColor to my theme color.

2: The second group uses the MAUI RadioButton with a control template.

3: The third group uses a custom RadioGroup. This ties the radio ellipse color to the TextColor. IsChecked is indicated by drawing a thicker ellipse.

3: The fourth group uses a custom RadioGroup with an ItemTemplate.

When the application follows the system theme (AppTheme.Unspecialized), the RadioButton displays reasonable colors when the system switches between light and dark. When an explicit them is selected, parts of the Maui RadioButton do not change.

This suggests there are color settings that the RadioButton uses that are not defined in my custom themes under Resources\Themes.

Additionally, in RadioButton with a ControlTemplate, attempting to mirror the Ellipse color with the color used by the non-templated RadioButton fails in that the Ellipse does not reliably draw with the theme color. I've seen similar behavior when I defined a Checked and Unchecked color on the RadioGroup. Setting these to anything other than Primary Foreground/Background produces the same unpredictable results.

Is there a bug in Ellipse or in my Bindings logic. I dig further into this.

See dotnet/maui#11709

• Previously shown RadioButton with VisualState Manager becomes erratic after AppTheme is changed by user

See dotnet/maui#11747

• iOS Radio Button displays with same black coloring in Dark Mode

See dotnet/maui#13570

• Referencing a dynamic color in a DataTrigger does not work.