maui-theming — independently scanned and version-tracked by SaferSkills.
SaferSkills independently audited maui-theming (Agent Skill) and scored it 45/100 (orange). The audit ran 55 deterministic rules across Security, Supply Chain, Maintenance, Transparency, and Community; it found 7 high-severity and 0 lower-severity findings. The full rule-by-rule trace and per-finding evidence are below. Free, methodology-open.
Findings & checks · 7 flagged
A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.A base64 string of 128+ characters appears in a documentation file. Encoded prompt injection hides the hostile instruction in base64 — invisible to keyword filters — and relies on the agent's ability to decode it at runtime. There is no normal authoring reason to embed a multi-hundred-byte base64 blob in skill docs.
*.sig, SIGNATURES) outside the documentation.Every scanned point with the score it earned and what moved between them.
First recorded scan — no prior version to compare against.
The primary manifest — the file an agent reads to learn what this artifact does.
Apply light/dark mode support, custom branded themes, and runtime theme switching in .NET MAUI apps using AppThemeBinding, ResourceDictionary swapping, and system theme detection APIs.
Plugin.Maui.BootstrapTheme NuGet packageAppThemeBinding values or separate ResourceDictionary files with matching keys.DynamicResource bindings (or AppThemeBinding markup) throughout XAML pages.Application.Current.RequestedTheme and the RequestedThemeChanged event.Preferences.Set / Preferences.Get and apply on startup.ConfigChanges.UiMode is set on MainActivity to avoid activity restarts on theme change.Check these rules against the user's scenario, and apply only the ones that affect what they asked. UiMode and dictionary swapping matter for runtime theme switching; they are noise in a question about setting up AppThemeBinding.
Answer narrowly, but completely. Completeness means showing the code that implements what you recommended — not adding adjacent topics. If you recommend DynamicResource, show the dictionary swap that makes it update. If the user asks for light/dark colours in C#, show both SetAppThemeColor (colours) and the generic SetAppTheme<T> (any bindable property type), and prefer resource keys over scattered hardcoded colours. Do not tack on platform configuration the question didn't raise.
| Rule | Do this | Not this | Why |
|---|---|---|---|
| Runtime-swapped values must be dynamic | {DynamicResource Key} | {StaticResource Key} | StaticResource resolves once at load and never updates when dictionaries are swapped. |
| Android must declare `UiMode` (only for runtime/system theme switching) | Include ConfigChanges.UiMode in the ConfigurationChanges list on MainActivity | Omitting it | Without it Android restarts the activity on theme change — navigation state is lost and it looks like a crash. Irrelevant to a static AppThemeBinding setup |
| Force a theme via `UserAppTheme` | Application.Current.UserAppTheme = AppTheme.Dark | Manually re-assigning colors | UserAppTheme overrides the OS; AppTheme.Unspecified returns to following the system. |
Do not replace a working AppThemeBinding setup with ResourceDictionary swapping (or vice versa) unless the user needs what the other approach provides — more than two themes, or a user-selectable theme.
| Approach | Best for | Limitation |
|---|---|---|
| AppThemeBinding | Automatic light/dark with OS — minimal code | Only two themes (light + dark) |
| ResourceDictionary swap | Custom branded themes, more than two themes, user preference | More setup; must use DynamicResource everywhere |
| Both combined | OS-driven response plus custom theme colors | Most flexible but most complex |
AppThemeBinding selects a value based on the current system theme. It supports Light, Dark, and an optional Default fallback.
Putting {AppThemeBinding Light=#333333, Dark=#FFFFFF} on every element is the single most common theming mistake: the palette ends up duplicated across dozens of files and cannot be changed in one place. Recommend this shape as the final answer, not inline literals:
<!-- App.xaml — one source of truth for the whole app -->
<Application.Resources>
<ResourceDictionary>
<!-- 1. Raw palette -->
<Color x:Key="LightPageBackground">#FFFFFF</Color>
<Color x:Key="DarkPageBackground">#1E1E1E</Color>
<Color x:Key="LightPrimaryText">#333333</Color>
<Color x:Key="DarkPrimaryText">#E0E0E0</Color>
<!-- 2. Implicit styles bind the pair once; every page inherits them -->
<Style TargetType="ContentPage" ApplyToDerivedTypes="True">
<Setter Property="BackgroundColor"
Value="{AppThemeBinding Light={StaticResource LightPageBackground},
Dark={StaticResource DarkPageBackground}}" />
</Style>
<Style TargetType="Label">
<Setter Property="TextColor"
Value="{AppThemeBinding Light={StaticResource LightPrimaryText},
Dark={StaticResource DarkPrimaryText}}" />
</Style>
</ResourceDictionary>
</Application.Resources>Pages then need no theming markup at all — they pick the styles up implicitly. Use an inline AppThemeBinding only for genuine one-offs, and even then reference {StaticResource} keys rather than literal hex.
<Label Text="Themed text"
TextColor="{AppThemeBinding Light=Green, Dark=Red}"
BackgroundColor="{AppThemeBinding Light=White, Dark=Black}" />
<!-- With resource references — preferred over literals -->
<Label TextColor="{AppThemeBinding Light={StaticResource LightPrimary},
Dark={StaticResource DarkPrimary}}" />Show both when answering a "light/dark colours in C#" question — SetAppThemeColor covers Color properties, SetAppTheme<T> covers everything else:
var label = new Label();
// Color-specific helper
label.SetAppThemeColor(Label.TextColorProperty, Colors.Green, Colors.Red);
// Generic helper — works for any bindable property type, not just Color
label.SetAppTheme<Color>(Label.TextColorProperty, Colors.Green, Colors.Red);
label.SetAppTheme<double>(Label.FontSizeProperty, 14, 16);
// The BindableProperty must belong to the object you call it on —
// Image.SourceProperty goes on an Image, not a Label.
var image = new Image();
image.SetAppTheme<ImageSource>(Image.SourceProperty,
ImageSource.FromFile("logo_light.png"),
ImageSource.FromFile("logo_dark.png"));Prefer defining the values as resource keys and referencing them, rather than scattering hardcoded colours across the codebase.
Use separate ResourceDictionary files with matching keys to define themes, then swap them at runtime.
When using compiled XAML with x:Class (as shown below), each dictionary needs a code-behind that calls InitializeComponent(). Dictionaries loaded via Source without x:Class do not need code-behind.
LightTheme.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MyApp.Themes.LightTheme">
<Color x:Key="PageBackgroundColor">White</Color>
<Color x:Key="PrimaryTextColor">#333333</Color>
<Color x:Key="AccentColor">#2196F3</Color>
</ResourceDictionary>LightTheme.xaml.cs
namespace MyApp.Themes;
public partial class LightTheme : ResourceDictionary
{
public LightTheme() => InitializeComponent();
}Create a matching DarkTheme.xaml / DarkTheme.xaml.cs with the same keys and different values.
Use DynamicResource so values update when the dictionary is swapped at runtime:
<ContentPage BackgroundColor="{DynamicResource PageBackgroundColor}">
<Label Text="Hello"
TextColor="{DynamicResource PrimaryTextColor}" />
<Button Text="Action"
BackgroundColor="{DynamicResource AccentColor}" />
</ContentPage>🚨 Never call `MergedDictionaries.Clear()` to swap a theme. The default MAUI template mergesResources/Styles/Colors.xamlandStyles.xamlintoApplication.Resources.Clear()removes those too, so every implicit style, brush and colour in the app silently disappears — buttons, entries and labels all revert to unstyled defaults. Verified: afterClear(),MergedDictionariesdrops from 2 to 1 and the template'sPrimarycolour no longer resolves.
Remove only the theme you added, and leave everything else alone:
static ResourceDictionary? _currentTheme;
void ApplyTheme(ResourceDictionary theme)
{
var merged = Application.Current!.Resources.MergedDictionaries;
// ✅ Remove ONLY the previous theme — Colors.xaml / Styles.xaml survive
if (_currentTheme is not null)
merged.Remove(_currentTheme);
merged.Add(theme);
_currentTheme = theme;
}
// Usage
ApplyTheme(new DarkTheme());// ❌ Destroys the app's Colors.xaml and Styles.xaml along with the old theme
var merged = Application.Current!.Resources.MergedDictionaries;
merged.Clear();
merged.Add(theme);AppTheme currentTheme = Application.Current!.RequestedTheme;
// Returns AppTheme.Light, AppTheme.Dark, or AppTheme.Unspecified// Force dark mode regardless of OS setting
Application.Current!.UserAppTheme = AppTheme.Dark;
// Reset to follow system theme
Application.Current!.UserAppTheme = AppTheme.Unspecified;Application.Current!.RequestedThemeChanged += (s, e) =>
{
AppTheme newTheme = e.RequestedTheme;
// Update UI or switch ResourceDictionaries
};Use AppThemeBinding with DynamicResource values for maximum flexibility — the nested DynamicResource stays live, so swapping the dictionary updates the value and the OS light/dark switch is still honoured:
<Label TextColor="{AppThemeBinding
Light={DynamicResource LightPrimary},
Dark={DynamicResource DarkPrimary}}" />Or react to system changes and swap full dictionaries:
Application.Current!.RequestedThemeChanged += (s, e) =>
{
ApplyTheme(e.RequestedTheme == AppTheme.Dark
? new DarkTheme()
: new LightTheme());
};Store the user's choice with Preferences and apply it on startup:
// Save choice
Preferences.Set("AppTheme", "Dark");
// Restore on startup (in App constructor or CreateWindow)
var saved = Preferences.Get("AppTheme", "System");
Application.Current!.UserAppTheme = saved switch
{
"Light" => AppTheme.Light,
"Dark" => AppTheme.Dark,
_ => AppTheme.Unspecified
};MainActivity must include ConfigChanges.UiMode or theme-change events will not fire and the activity restarts instead of handling the change gracefully:
[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. With it declared, the app stays alive and RequestedThemeChanged fires, so pair this fix with a handler that re-applies the theme (see below).
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}" />DynamicResource only helps if something actually swaps the dictionary. When you diagnose this, always show the swap and the system-theme hook alongside the fix — otherwise the user has a corrected binding that still never updates:
static ResourceDictionary? _currentTheme;
void ApplyTheme(bool useDark)
{
var merged = Application.Current!.Resources.MergedDictionaries;
// Remove only the previous theme — never Clear(), which also wipes
// the template's Colors.xaml / Styles.xaml
if (_currentTheme is not null)
merged.Remove(_currentTheme);
_currentTheme = useDark ? new DarkTheme() : new LightTheme();
merged.Add(_currentTheme);
}
// React to the OS switching light/dark
Application.Current!.RequestedThemeChanged += (s, e) =>
ApplyTheme(e.RequestedTheme == AppTheme.Dark);Avoid inline color values on elements that should respect the theme:
<!-- ❌ Will not change with theme -->
<Label TextColor="#333333" />
<!-- ✅ Theme-aware -->
<Label TextColor="{DynamicResource PrimaryTextColor}" />.NET MAUI supports CSS styling, but CSS-based themes cannot be swapped dynamically. Use ResourceDictionary theming for runtime switching.
Every x:Key used in one theme dictionary must exist in all other theme dictionaries. A missing key causes a silent fallback to the default value, leading to inconsistent appearance.
| Platform | Minimum Version |
|---|---|
| iOS | 13+ |
| Android | 10+ (API 29) |
| macOS Catalyst | 10.15+ |
| Windows | 10+ |
AppThemeBinding markup extensionSetAppThemeColor(), SetAppTheme<T>()Application.Current.RequestedThemeApplication.Current.UserAppTheme = AppTheme.DarkRequestedThemeChanged eventRemove the old theme from MergedDictionaries, then Add the new one — never `Clear()`StaticResource)Preferences.Set / Preferences.Get~30 seconds. Free. No account. Every finding cites a rule and a line of evidence.