dotnet-maui-aot
SKILL.md
dotnet-maui-aot
Native AOT compilation for .NET MAUI on iOS and Mac Catalyst: compilation pipeline, publish profiles, up to 50% app size reduction and up to 50% startup improvement, library compatibility gaps, opt-out mechanisms, trimming interplay (RD.xml, source generators), and testing AOT builds on device.
Version assumptions: .NET 8.0+ baseline. Native AOT for MAUI is available on iOS and Mac Catalyst. Android uses a different compilation model (CoreCLR in .NET 11, Mono/AOT in .NET 8-10).
Scope
- iOS/Mac Catalyst AOT compilation pipeline
- Publish profile configuration for MAUI AOT
- Size/startup improvement measurements
- Library compatibility gaps for MAUI AOT apps
- Opt-out mechanisms and trimming interplay
- Testing AOT builds on device
Out of scope
- MAUI development patterns (project structure, XAML, MVVM) -- see [skill:dotnet-maui-development]
- MAUI testing -- see [skill:dotnet-maui-testing]
- WASM AOT (Blazor/Uno) -- see [skill:dotnet-aot-wasm]
- General AOT architecture -- see [skill:dotnet-native-aot]
Cross-references: [skill:dotnet-maui-development] for MAUI patterns, [skill:dotnet-maui-testing] for testing AOT builds, [skill:dotnet-native-aot] for general AOT patterns, [skill:dotnet-aot-wasm] for WASM AOT, [skill:dotnet-ui-chooser] for framework selection.
iOS/Mac Catalyst AOT Compilation Pipeline
Native AOT on iOS and Mac Catalyst compiles .NET IL directly to native machine code at publish time, eliminating the need for a JIT compiler or IL interpreter at runtime. This produces a self-contained native binary that links against platform frameworks.
How It Works
- IL compilation: The .NET IL is compiled to native code by the NativeAOT compiler (ILC)
- Tree shaking: Unused code is trimmed based on static analysis of reachable types and methods
- Native linking: The generated native code is linked with iOS/Catalyst frameworks and the minimal .NET runtime
- App bundle: The result is a standard
.appbundle with a native executable (no IL assemblies shipped)
Publish Configuration
<!-- Enable Native AOT for iOS/Mac Catalyst -->
<PropertyGroup Condition="'$(TargetFramework)' == 'net8.0-ios' Or
'$(TargetFramework)' == 'net8.0-maccatalyst'">
<PublishAot>true</PublishAot>
<!-- Optional: strip debug symbols for smaller binary -->
<StripSymbols>true</StripSymbols>
</PropertyGroup>
```text
```bash
# Publish with AOT for iOS
dotnet publish -f net8.0-ios -c Release -r ios-arm64
# Publish with AOT for Mac Catalyst
dotnet publish -f net8.0-maccatalyst -c Release -r maccatalyst-arm64
# Publish for iOS simulator (for AOT testing without device)
dotnet publish -f net8.0-ios -c Release -r iossimulator-arm64
```text
### Entitlements and Provisioning
AOT builds require the same entitlements and provisioning profiles as regular iOS/Catalyst builds. No additional
entitlements are needed for AOT specifically.
```xml
<!-- iOS entitlements (Entitlements.plist) -->
<!-- Standard entitlements; AOT does not require special entries -->
```xml
---
## Size Reduction
Native AOT can achieve **up to 50% app size reduction** compared to interpreter/JIT mode on iOS. The size improvement
comes from:
- **Tree shaking:** Only reachable code is included in the final binary
- **No IL shipping:** The app bundle does not include .NET IL assemblies
- **No runtime JIT:** The JIT compiler and associated metadata are not packaged
### Typical Size Comparison
| Mode | Approximate Size | Notes |
| -------------------------------- | ---------------- | ------------------------------------ |
| Interpreter (default .NET 8 iOS) | ~60-80 MB | Includes IL assemblies + interpreter |
| Native AOT | ~30-45 MB | Native binary only, no IL |
| Native AOT + StripSymbols | ~25-40 MB | Debug symbols stripped |
**Caveat:** Actual size reduction depends on app complexity, third-party library usage, and how much code is reachable
after trimming. Libraries that use heavy reflection may prevent aggressive trimming and reduce size gains.
---
## Startup Improvement
Native AOT provides **up to 50% faster cold startup** on iOS and Mac Catalyst. The startup improvement comes from:
- **No JIT warmup:** Code is already native; no compilation at app launch
- **No IL loading:** No need to load and parse .NET assemblies
- **Reduced memory pressure:** Smaller working set during startup
### Measuring Startup
```csharp
// Instrument startup timing
public partial class App : Application
{
private static readonly long StartTicks = Stopwatch.GetTimestamp();
public App()
{
InitializeComponent();
MainPage = new AppShell();
var elapsed = Stopwatch.GetElapsedTime(StartTicks);
System.Diagnostics.Debug.WriteLine(
$"App startup: {elapsed.TotalMilliseconds:F0}ms");
}
}
```text
```bash
# Use Xcode Instruments for precise startup measurement
# Time Profiler template → measure "pre-main" + "post-main" time
# Compare AOT vs non-AOT builds on the same device
```bash
---
## Library Compatibility
Many .NET libraries are not fully AOT-compatible. Common compatibility issues stem from:
- **Reflection:** Runtime type inspection, `Type.GetType()`, `Activator.CreateInstance()`
- **Dynamic code generation:** `System.Reflection.Emit`, `System.Linq.Expressions.Compile()`
- **Serialization without source generators:** JSON/XML serializers that use reflection
### Compatibility Matrix
| Library / Feature | AOT Status | Workaround |
| ----------------------------- | ---------- | ----------------------------------------------------------------------------- |
| System.Text.Json (source gen) | Compatible | Use `[JsonSerializable]` context |
| System.Text.Json (reflection) | Breaks | Switch to source generators |
| CommunityToolkit.Mvvm | Compatible | Source-gen based, AOT-safe |
| Entity Framework Core | Partial | Precompiled queries; no dynamic LINQ |
| Newtonsoft.Json | Breaks | Migrate to System.Text.Json with source gen |
| AutoMapper | Breaks | Use Mapperly (source gen) |
| MediatR | Partial | Register handlers explicitly, avoid assembly scanning |
| HttpClient | Compatible | Standard usage works |
| MAUI Essentials | Compatible | Platform APIs are AOT-safe |
| SQLite-net | Compatible | Uses P/Invoke, AOT-safe |
| Refit | Breaks | Use Refit 7+ (includes source generator; enable with `[GenerateRefitClient]`) |
| FluentValidation | Partial | Avoid runtime expression compilation |
### Detecting Incompatible Code
```xml
<!-- Enable AOT analysis warnings during development -->
<PropertyGroup>
<EnableAotAnalyzer>true</EnableAotAnalyzer>
<!-- Also enable trim analyzer (AOT requires trimming) -->
<EnableTrimAnalyzer>true</EnableTrimAnalyzer>
</PropertyGroup>
```text
AOT analysis produces warnings like `IL3050` (RequiresDynamicCode) and `IL2026` (RequiresUnreferencedCode). Address
these before publishing with AOT.
---
## Opt-Out Mechanisms
### Disabling AOT Entirely
```xml
<!-- Disable Native AOT (use interpreter/JIT mode) -->
<PropertyGroup>
<PublishAot>false</PublishAot>
</PropertyGroup>
```text
### Per-Assembly Trimming Overrides
When a specific library is not AOT-compatible, you can preserve it from trimming while still using AOT for the rest of
the app:
```xml
<!-- Preserve a specific assembly from trimming -->
<ItemGroup>
<TrimmerRootAssembly Include="IncompatibleLibrary" />
</ItemGroup>
```text
### Opt-Out of .NET 11 Defaults
.NET 11 introduces new defaults that interact with AOT:
```xml
<!-- Revert XAML source gen (use legacy XAMLC) -->
<PropertyGroup>
<MauiXamlInflator>XamlC</MauiXamlInflator>
</PropertyGroup>
<!-- Revert to Mono runtime on Android (not related to iOS AOT,
but relevant for the overall MAUI AOT story) -->
<PropertyGroup>
<UseMonoRuntime>true</UseMonoRuntime>
</PropertyGroup>
```text
---
## Trimming Interplay
Native AOT requires trimming. When `PublishAot` is true, trimming is automatically enabled. Understanding trimming
configuration is essential for a successful AOT build.
### ILLink Descriptors for Reflection Preservation
> **Note:** In Xamarin/Mono-era documentation, these were called "rd.xml" (Runtime Directives). In .NET 8+ Native AOT,
> use ILLink descriptor XML files instead.
When code uses reflection that the trimmer cannot statically analyze, use an ILLink descriptor XML file to preserve
types. You can also use `[DynamicDependency]` attributes for fine-grained preservation in code.
**ILLink descriptor XML (preferred for bulk preservation):**
```xml
<!-- ILLink.Descriptors.xml -- preserve types needed at runtime -->
<linker>
<!-- Preserve all public members of a type -->
<assembly fullname="MyApp">
<type fullname="MyApp.Models.LegacyConfig" preserve="all" />
<type fullname="MyApp.Services.PluginLoader">
<method name="LoadPlugin" />
</type>
</assembly>
<!-- Preserve all types in an external assembly -->
<assembly fullname="IncompatibleLibrary" preserve="all" />
</linker>
```text
```xml
<!-- Register the descriptor in .csproj -->
<ItemGroup>
<TrimmerRootDescriptor Include="ILLink.Descriptors.xml" />
</ItemGroup>
```csharp
**`[DynamicDependency]` attribute (preferred for targeted preservation):**
```csharp
using System.Diagnostics.CodeAnalysis;
// Preserve a specific method on a type
[DynamicDependency(nameof(LegacyConfig.Initialize), typeof(LegacyConfig))]
public void ConfigureApp() { /* ... */ }
// Preserve all public members of a type
[DynamicDependency(DynamicallyAccessedMemberTypes.All, typeof(LegacyConfig))]
public void LoadPlugins() { /* ... */ }
```text
### Source Generator Alternatives
When source generators aren't available, use `[DynamicDependency]` attributes (shown above) for targeted preservation
without ILLink XML files.
Prefer source generators over reflection to avoid trimming issues entirely:
| Reflection Pattern | Source Generator Alternative |
| --------------------------------- | ----------------------------------------------- |
| `JsonSerializer.Deserialize<T>()` | `[JsonSerializable]` context (System.Text.Json) |
| `Activator.CreateInstance<T>()` | Factory pattern with explicit registration |
| `Type.GetProperties()` | CommunityToolkit.Mvvm `[ObservableProperty]` |
| Assembly scanning for DI | Explicit `services.Add*()` registrations |
| AutoMapper reflection mapping | Mapperly `[Mapper]` source generator |
### Trimming Warnings
```bash
# Build with detailed trim warnings
dotnet publish -f net8.0-ios -c Release /p:PublishAot=true /p:TrimmerSingleWarn=false
# TrimmerSingleWarn=false shows per-occurrence warnings instead of
# one summary warning per assembly, making it easier to fix issues
```text
Common trim warnings:
- **IL2026:** Member with `RequiresUnreferencedCode` -- the member does something not guaranteed to work after trimming
- **IL2046:** Trim attribute mismatch between base/derived types
- **IL3050:** Member with `RequiresDynamicCode` -- the member generates code at runtime (incompatible with AOT)
---
## Testing AOT Builds
AOT builds can behave differently from Debug/JIT builds. Always test on a real device or simulator with an AOT-published
build before release.
### Common AOT-Only Failures
| Failure | Symptom | Fix |
| ------------------------------ | ------------------------------------- | ---------------------------------------------------------- |
| Missing type metadata | `MissingMetadataException` at runtime | Add type to ILLink descriptor or use `[DynamicDependency]` |
| Trimmed method | `MissingMethodException` | Add `[DynamicDependency]` or ILLink descriptor entry |
| Dynamic code gen | `PlatformNotSupportedException` | Replace with source generator alternative |
| Reflection-based serialization | Empty/null deserialized objects | Use `[JsonSerializable]` source gen |
| Assembly scanning | Missing services at runtime | Register services explicitly in DI |
### Testing Workflow
```bash
# 1. Build and publish with AOT for simulator (faster iteration)
dotnet publish -f net8.0-ios -c Release -r iossimulator-arm64
# 2. Install and test on simulator
# (Use Xcode or Visual Studio to deploy the .app to simulator)
# 3. Run smoke tests -- focus on:
# - App startup (no MissingMetadataException)
# - JSON deserialization (all properties populated)
# - Navigation (all pages render)
# - Platform services (biometric, camera, location)
# - Third-party SDK integration
# 4. Test on physical device before release
dotnet publish -f net8.0-ios -c Release -r ios-arm64
# Deploy via Xcode with provisioning profile
```text
### CI Integration
```bash
# CI pipeline: build AOT and run device tests via XHarness
dotnet publish -f net8.0-ios -c Release -r iossimulator-arm64 /p:PublishAot=true
xharness apple test \
--app bin/Release/net8.0-ios/iossimulator-arm64/publish/MyApp.app \
--target ios-simulator-64 \
--timeout 00:10:00 \
--output-directory test-results/aot
```text
For MAUI testing patterns (Appium, XHarness), see [skill:dotnet-maui-testing].
---
## Agent Gotchas
1. **Do not enable `PublishAot` without also enabling trim analyzers.** AOT requires trimming. Set
`<EnableTrimAnalyzer>true</EnableTrimAnalyzer>` and `<EnableAotAnalyzer>true</EnableAotAnalyzer>` during development
to catch issues early.
2. **Do not assume all NuGet packages are AOT-compatible.** Check for `IsAotCompatible` in the package's `.csproj` or
look for trim/AOT warnings when building. Many popular packages still use reflection internally.
3. **Do not use `Newtonsoft.Json` with AOT.** It relies entirely on reflection. Migrate to `System.Text.Json` with
`[JsonSerializable]` source gen contexts for AOT-safe serialization.
4. **Do not skip device testing for AOT builds.** Simulator testing catches most issues, but physical device behavior
can differ -- especially for startup timing, memory constraints, and platform service integration.
5. **Do not confuse MAUI iOS AOT with Android AOT.** MAUI Native AOT (`PublishAot`) targets iOS and Mac Catalyst only.
Android uses a different compilation model (Mono AOT in .NET 8-10, CoreCLR in .NET 11+). They are configured
separately.
---
## Prerequisites
- .NET 8.0+ with MAUI workload
- Xcode and iOS/Mac Catalyst SDKs (macOS only)
- Apple Developer account for physical device deployment
- Provisioning profile and signing certificate for device testing
---
## References
- [MAUI Native AOT](https://learn.microsoft.com/en-us/dotnet/maui/deployment/nativeaot)
- [Native AOT Deployment](https://learn.microsoft.com/en-us/dotnet/core/deploying/native-aot/)
- [Trim Self-Contained Applications](https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trimming-options)
- [Prepare .NET Libraries for Trimming](https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/prepare-libraries-for-trimming)
- [Trimming Descriptor Format](https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trimming-options#descriptor-format)
- [.NET 11 Preview 1 Announcement](https://devblogs.microsoft.com/dotnet/dotnet-11-preview-1/)
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