Dotnet Maui 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

1. IL compilation: The .NET IL is compiled to native code by the NativeAOT compiler (ILC)
2. Tree shaking: Unused code is trimmed based on static analysis of reachable types and methods
3. Native linking: The generated native code is linked with iOS/Catalyst frameworks and the minimal .NET runtime
4. App bundle: The result is a standard .app bundle 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/)