Android中添加C或C++代码

1、创建cpp目录，用于存放C和C++代码。

2、创建CMake构建脚本CMakeLists.txt文件，将其放在cpp目录中。

# Sets the minimum version of CMake required to build the native library.
cmake_minimum_required(VERSION 3.22.1)

# Declares and names the project.
project("test-project")

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.
add_library( # Sets the name of the library.
        test

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        test.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.
find_library( # Sets the name of the path variable.
        log-lib

        # Specifies the name of the NDK library that
        # you want CMake to locate.
        log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
        test

        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

3、配置CMakeLists.txt文件路径和CMake的版本，使CMake工具能够编译该文件。在app中的build.gradle加入以下代码。

4、创建test.cpp用于测试。

#include <jni.h>
#include <android/log.h>

extern "C"
JNIEXPORT void JNICALL
Java_com_example_cmakelisttest_MainActivity_testMethod(JNIEnv *env, jobject) {
    __android_log_print(ANDROID_LOG_INFO,"TAG","Hello Native!");
}

5、加载C或C++代码生成的so库，并调用其中的方法。

public class MainActivity extends AppCompatActivity {

    static {
        System.loadLibrary("test"); // 加载生成的so库
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        testMethod(); // 调用native方法
    }

    public native void testMethod(); // 定义native方法
}

6、运行该程序，如果成功，则会打印"Hello Native!"。

附录：文件结构图