# Maui Theming

> Guide for theming .NET MAUI apps—light/dark mode support, AppThemeBinding, dynamic resources, ResourceDictionary theme switching, and system theme detection. USE FOR: "dark mode", "light mode", "theming", "AppThemeBinding", "theme switching", "ResourceDictionary theme", "dynamic resources", "system theme detection", "color scheme", "app theme". DO NOT USE FOR: localization or language switching (use maui-localization), accessibility visual adjustments (use maui-accessibility), or app icons (use maui-app-icons-splash).

- Skill: `davidortinau/maui-theming` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add davidortinau/maui-theming`
- Raw SKILL.md: https://api.skillmd.com/api/skills/davidortinau/maui-theming/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: davidortinau (https://skillmd.com/u/davidortinau)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/davidortinau/maui-theming

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# .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:

```csharp
[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`:

```xml
<!-- ✅ 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`)