Android
There are several ways to cross-compile packages for Android platform via conan.
Using android_ndk_installer package (build require)
The easiest way so far is to use android_ndk_installer conan package (which is in conan-center repository).
Using the android_ndk_installer package as a build requirement will do the following steps:
Download the appropriate Android NDK archive.
Set up required environment variables, such as
CC,CXX,RANLIBand so on to the appropriate tools from the NDK.In case of using CMake, it will inject the appropriate toolchain file and set up the necessary CMake variables.
For instance, in order to cross-compile for ARMv8, the following conan profile might be used:
include(default)
[settings]
arch=armv8
build_type=Release
compiler=clang
compiler.libcxx=libc++
compiler.version=8
os=Android
os.api_level=21
[build_requires]
android_ndk_installer/r20@bincrafters/stable
[options]
[env]
Note
In addition to the above, Windows users may need to specify CONAN_MAKE_PROGRAM,
for instance from the existing MinGW installation (e.g. C:\MinGW\bin\mingw32-make.exe), or use make from the mingw_installer/1.0@conan/stable.
Similar profile might be used to cross-compile for ARMv7 (notice the arch change):
include(default)
[settings]
arch=armv7
build_type=Release
compiler=clang
compiler.libcxx=libc++
compiler.version=8
os=Android
os.api_level=21
[build_requires]
android_ndk_installer/r20@bincrafters/stable
[options]
[env]
By adjusting arch setting, you may cross-compile for x86 and x86_64 Android as well (e.g. if you need to run code in a simulator).
Note
os.api_level is an important setting which affects compatibility - it defines the minimum Android version supported.
In other words, it is the same meaning as minSdkVersion.
Use built-in Conan toolchain
Warning
This is an experimental feature subject to breaking changes in future releases.
Conan will generate a toolchain for Android if the recipe is using a CMakeToolchain. In that case all you need is to provide the path to the Android NDK and working profiles. This approach can also use the Android NDK package referenced in the previous section.
Use a regular profile for the host context:
[settings]
os=Android
os.api_level=23
arch=x86_64
compiler=clang
compiler.version=9
compiler.libcxx=c++_shared
build_type=Release
and add Android NDK to the PATH or populate the CONAN_CMAKE_ANDROID_NDK environment variable.
Together with the files created by the generators that make it possible to find and link the requirements, conan install command will generate a toolchain file like the following one:
set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose the type of build." FORCE)
set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_SYSTEM_VERSION 23)
set(CMAKE_ANDROID_ARCH_ABI x86_64)
set(CMAKE_ANDROID_STL_TYPE c++_shared)
set(CMAKE_ANDROID_NDK <path/provided/via/environment/variable>)
With this toolchain file you can execute CMake’s command to generate the binaries:
conan install <conanfile> --profile:host=profile_host --profile:build=default
cmake . -DCMAKE_TOOLCHAIN_FILE=conan_toolchain.cmake
cmake --build . --config Release
Using Docker images
If you’re using Docker for builds, you may consider using docker images from the Conan Docker Tools repository.
Currently, Conan Docker Tools provide the following Android images:
conanio/android-clang8
conanio/android-clang8-x86
conanio/android-clang8-armv7
conanio/android-clang8-armv8
All above mentioned images have corresponding Android NDK installed, with required environment variables set and with default conan profile configured for android cross-building. Therefore, these images might be especially useful for CI systems.
Using existing NDK
It’s also possible to use an existing Android NDK installation with conan.
For instance, if you’re using Android Studio IDE, you may already have an NDK at ~/Library/Android/sdk/ndk.
You have to specify different environment variables in the Conan profile for make-based projects. For instance:
include(default)
target_host=aarch64-linux-android
android_ndk=/home/conan/Library/Android/sdk/ndk/20.0.5594570
api_level=21
[settings]
arch=armv8
build_type=Release
compiler=clang
compiler.libcxx=libc++
compiler.version=8
os=Android
os.api_level=$api_level
[build_requires]
[options]
[env]
PATH=[$android_ndk/toolchains/llvm/prebuilt/darwin-x86_64/bin]
CHOST=$target_host
AR=$target_host-ar
AS=$target_host-as
RANLIB=$target_host-ranlib
CC=$target_host$api_level-clang
CXX=$target_host$api_level-clang++
LD=$target_host-ld
STRIP=$target_host-strip
However, when building CMake projects, there are several approaches available, and it’s not always clear which one to follow.
Using toolchain from Android NDK
This is the official way recommended by Android developers.
For this, you will need a small CMake toolchain file:
set(ANDROID_PLATFORM 21)
set(ANDROID_ABI arm64-v8a)
include($ENV{HOME}/Library/Android/sdk/ndk/20.0.5594570/build/cmake/android.toolchain.cmake)
This toolchain file only sets up the required CMake variables, and then includes the default toolchain file supplied with Android NDK.
And then, you may use the following profile:
include(default)
[settings]
arch=armv8
build_type=Release
compiler=clang
compiler.libcxx=libc++
compiler.version=8
os=Android
os.api_level=21
[build_requires]
[options]
[env]
CONAN_CMAKE_TOOLCHAIN_FILE=/home/conan/my_android_toolchain.cmake
In the profile, CONAN_CMAKE_TOOLCHAIN_FILE points to the CMake toolchain file listed above.
Using CMake build-in Android NDK support
Warning
This workflow is not supported by Android and is often broken with new NDK releases or when using older versions of CMake. This workflow is strongly discouraged and will not work with Gradle.
For this approach, you don’t need to specify CMake toolchain file at all. It’s enough to indicate os is Android
and Conan will automatically set up all required CMake
variables for you.
Therefore, the following conan profile could be used for ARMv8:
include(default)
[settings]
arch=armv8
build_type=Release
compiler=clang
compiler.libcxx=libc++
compiler.version=7.0
os=Android
os.api_level=21
[build_requires]
[options]
[env]
ANDROID_NDK_ROOT=/home/conan/android-ndk-r18b
The only way you have to configure is ANDROID_NDK_ROOT which is a path to the Android NDK installation.
Once profile is configured, you should see the following output during the CMake build:
-- Android: Targeting API '21' with architecture 'arm64', ABI 'arm64-v8a', and processor 'aarch64'
-- Android: Selected Clang toolchain 'aarch64-linux-android-clang' with GCC toolchain 'aarch64-linux-android-4.9'
It means native CMake integration has successfully found Android NDK and configured the build.