.NET MAUI Theming

Choosing your approach

| Approach | Best for | Limitation | |----------|----------|------------| | AppThemeBinding | Auto light/dark with OS — minimal code | Only two themes (light + dark) | | ResourceDictionary swap | Custom branded themes, >2 themes, user preference | More setup, must use DynamicResource everywhere | | Both combined | Auto OS response + custom theme colors | Most flexible but most complex |

Critical gotchas

Android: ConfigChanges.UiMode is REQUIRED

MainActivity must include ConfigChanges.UiMode or theme change events will not fire and the activity restarts instead of handling the change:

[Activity(Theme = "@style/Maui.SplashTheme",
          MainLauncher = true,
          ConfigurationChanges = ConfigChanges.ScreenSize
                               | ConfigChanges.Orientation
                               | ConfigChanges.UiMode  // ← Required for theme detection
                               | ConfigChanges.ScreenLayout
                               | ConfigChanges.SmallestScreenSize
                               | ConfigChanges.Density)]
public class MainActivity : MauiAppCompatActivity { }

Without UiMode, toggling dark mode in Android settings causes a full activity restart — losing navigation state and appearing as a crash to users.

CSS themes cannot be swapped at runtime

MAUI supports CSS styling, but CSS-based themes cannot be swapped dynamically. Use ResourceDictionary theming for runtime switching.

DynamicResource vs StaticResource

When using ResourceDictionary theme switching, you must use DynamicResource:

<!-- ✅ Updates when theme dictionary changes -->
<Label TextColor="{DynamicResource PrimaryTextColor}" />

<!-- ❌ Frozen at first load — won't update on theme switch -->
<Label TextColor="{StaticResource PrimaryTextColor}" />

Quick reference

• OS light/dark → AppThemeBinding markup extension
• Theme colors in C# → SetAppThemeColor(), SetAppTheme<T>()
• Read OS theme → Application.Current.RequestedTheme
• Force theme → Application.Current.UserAppTheme = AppTheme.Dark
• Theme changes → RequestedThemeChanged event
• Custom switching → Swap ResourceDictionary in MergedDictionaries
• Runtime bindings → DynamicResource (not StaticResource)