Android-NativeAOT

A .NET 8, NativeAOT example on Android.

Example using SkiaSharp

This sample has a C++ Android Studio project:

Uses Native Activity
No Java/Kotlin code
Configures OpenGL
Calls into C# / managed code
Managed code uses SkiaSharp for rendering a random Skia shader
Tap input randomly changes the shader

Some screenshots of the Skia content:

(Note these look completely smooth on a Pixel 5, I just tried to snap quick gifs with Vysor)

The C# side is a:

.NET 8 class library
Built with RID linux-bionic-arm64
Uses the SkiaSharp NuGet package, as one would.
- Used a nightly build of SkiaSharp, as I wanted a feature from Skia 3.0

App Size

The release .apk file of the SkiaSharp sample is ~4.26 MB

A breakdown of the files inside:

> 7z l app-release.apk
   Date      Time    Attr         Size   Compressed  Name
------------------- ----- ------------ ------------  ------------------------
1981-01-01 01:01:02 .....           56           52  META-INF\com\android\build\gradle\app-metadata.properties
1981-01-01 01:01:02 .....         1524          753  classes.dex
1981-01-01 01:01:02 .....      8525024      3733033  lib\arm64-v8a\libSkiaSharp.so
1981-01-01 01:01:02 .....      1070792       473191  lib\arm64-v8a\libdotnet.so
1981-01-01 01:01:02 .....        19504         6869  lib\arm64-v8a\libnativeaot.so
1981-01-01 01:01:02 .....         2376          867  AndroidManifest.xml
1981-01-01 01:01:02 .....         7778         7778  res\-6.webp
1981-01-01 01:01:02 .....          548          239  res\0K.xml
1981-01-01 01:01:02 .....         5696          987  res\0w.xml
1981-01-01 01:01:02 .....          788          347  res\9s.xml
1981-01-01 01:01:02 .....          548          239  res\BW.xml
1981-01-01 01:01:02 .....         1404         1404  res\MO.webp
1981-01-01 01:01:02 .....         1572          703  res\PF.xml
1981-01-01 01:01:02 .....         2884         2884  res\Sn.webp
1981-01-01 01:01:02 .....          982          982  res\d2.webp
1981-01-01 01:01:02 .....         2898         2898  res\fq.webp
1981-01-01 01:01:02 .....         5914         5914  res\j_.webp
1981-01-01 01:01:02 .....         1900         1900  res\qs.webp
1981-01-01 01:01:02 .....         3844         3844  res\sK.webp
1981-01-01 01:01:02 .....         3918         3918  res\u5.webp
1981-01-01 01:01:02 .....         1772         1772  res\yw.webp
1981-01-01 01:01:02 .....         2036         2036  resources.arsc
1981-01-01 01:01:02 .....         2085         1122  META-INF\CERT.SF
1981-01-01 01:01:02 .....         1167         1021  META-INF\CERT.RSA
1981-01-01 01:01:02 .....         2011         1046  META-INF\MANIFEST.MF
------------------- ----- ------------ ------------  ------------------------
1981-01-01 01:01:02            9669021      4255799  25 files

libdotnet.so is ~1.07 MB, and libSkiaSharp.so is ~8.5MB!

If we reduce this to a "Hello World" example:

hello.apk is ~430 KB!
libdotnet.so (uncompressed) is ~821 KB!

Startup Time

The average of 10 runs on a Pixel 5 of the SkiaSharp sample:

Average(ms): 121
Std Err(ms): 3.29983164553722
Std Dev(ms): 10.434983894999

Average of 10 runs on a Pixel 5 of the "Hello World" example:

Average(ms): 120.9
Std Err(ms): 2.97937353594118
Std Dev(ms): 9.42160637400367

They might be effectively the same.

For comparison (as of .NET 8), a dotnet new android app is about ~180ms on a Pixel 5, and dotnet new maui is about ~560ms.

Source: https://github.com/jonathanpeppers/maui-profiling

"Hello World" Example

See the HelloWorld branch.

I had this managed code:

[UnmanagedCallersOnly(EntryPoint = "ManagedAdd")]
public static int ManagedAdd(int x, int y) => x + y;

I created a C++ Android project using NativeActivity, and I called the managed code from C++:

// in dotnet.h
extern "C" int ManagedAdd(int x, int y);

// in native-lib.cpp
int result = ManagedAdd(1, 2);
__android_log_print (ANDROID_LOG_INFO, TAG, "ManagedAdd(1, 2) returned: %i", result);

Results in the message:

01-31 11:42:44.545 28239 28259 I NATIVE  : Entering android_main
01-31 11:42:44.550 28239 28259 I NATIVE  : ManagedAdd(1, 2) returned: 3

See DotNet/README.md on how to build libdotnet.so.

Notes

Console.WriteLine() doesn't work because it basically just writes to Unix stdout. stdout does not appear in adb logcat output, as you have to call __android_log_print instead.

This was an interesting example, to start a thread that processes stdout and calls the appropriate Android API:

https://codelab.wordpress.com/2014/11/03/how-to-use-standard-output-streams-for-logging-in-android-apps/

Instead, we can p/invoke into:

[DllImport("log", EntryPoint = "__android_log_print", CallingConvention = CallingConvention.Cdecl)]
public static extern int LogPrint(LogPriority priority, string tag, string format);

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