Howdy there, fellow Android developers!Today we’re going to talk about something that can make your life a whole lot easier when building native libraries for the big green robot: CMake build scripts. If you’ve ever struggled with setting up complex builds or dealing with multiple platforms and configurations, this is definitely worth checking out.
To kick things off what exactly is CMake? It’s an open-source, cross-platform build system that can generate native makefiles and workspaces for a variety of different projects. In other words, it helps you automate the process of building your code on multiple platforms without having to write custom scripts or configure everything by hand.
Now Let’s roll with how we can use CMake to create build scripts specifically for Android native libraries. Here are some basic steps:
1. Create a new directory for your library and add your source files inside it. For example, if you have a library called “MyLibrary” with two source files (mylibrary.c and mylibrary_jni.cpp), create a folder named “MyLibrary” in your project’s root directory and put those files there.
2. Create a new CMakeLists.txt file inside the MyLibrary directory. This is where you’ll define how to build your library using CMake. Here’s an example:
# Set the minimum required version of CMake
cmake_minimum_required(VERSION 3.10)
# Project information
project(MyLibrary VERSION 1.0 LANGUAGES CXX)
# Set the target architecture for Android builds
set(CMAKE_ANDROID_ARCH_ABI "arm64-v8a")
# Set the minimum required API level (API 29 = Android Pie)
set(CMAKE_ANDROID_PLATFORM android-29)
# Choose STL implementation for Android builds
set(CMAKE_ANDROID_STL "gnustl_static" CACHE STRING "")
# Find and include any necessary external libraries or headers
find_package(log4cplus REQUIRED) # Find the log4cplus library
include_directories(${log4cplus_INCLUDE_DIRS}) # Include the header files from log4cplus in our build
# Set up source and include directories for MyLibrary
set(SOURCE_FILES mylibrary.c mylibrary_jni.cpp) # Define the source files for our library
set(HEADER_FILES include/mylibrary.h) # Define the header files for our library
include_directories(${CMAKE_CURRENT_LIST_DIR}/include) # Include the header files from our library in our build
# Set up target for MyLibrary
add_library(MyLibrary STATIC ${SOURCE_FILES}) # Create a static library called "MyLibrary" using the source files we defined earlier
target_link_libraries(MyLibrary log4cplus) # Link against any external libraries we need (in this case, log4cplus)
set_property(TARGET MyLibrary PROPERTY VERSION 1.0) # Set version number for our library
3. Save the CMakeLists.txt file and navigate to your project’s root directory in a terminal or command prompt. Run “cmake” followed by the path to your library’s directory:
# Change directory to the project's root directory
cd /path/to/your/project
# Create a build directory and change into it
mkdir build && cd build
# Run cmake on the MyLibrary directory to generate build files
cmake ../MyLibrary
This will generate makefiles and other configuration files for building on various platforms. For Android, you can then run “make” or “ninja” to compile your library:
# This script generates makefiles and other configuration files for building on various platforms.
# For Android, you can then run "make" or "ninja" to compile your library.
# Build with 4 threads (replace '4' with the number of cores on your machine)
make -j$(nproc) # Use the 'nproc' command to automatically determine the number of cores on the machine
# Install the library in /usr/local/lib for easy access from other projects
sudo make install # Use 'sudo' to run the command with root privileges, allowing installation in system directories
That’s it! You now have a CMake build script that can generate Android native libraries. Of course, this is just a basic example you may need to customize your build script based on your specific needs and requirements. But hopefully this gives you an idea of how powerful and flexible CMake can be for building complex projects with multiple platforms and configurations.