ndk和JNI的使用初探

参考资料:

https://blog.csdn.net/qq_25884515/article/details/104250920

创建C++项目

ndk和JNI的使用初探

理解 CMakeList.txt文件,

设置头文件和添加源文件

#设置头文件为当前路径
INCLUDE_DIRECTORIES("./")

# 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.
             native-lib
             # Sets the library as a shared library.
             SHARED
             # Provides a relative path to your source file(s).
             native-lib.cpp
             v4l2Cocos.cpp  )

还有在库里面调用库巴应该是

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

在 JAVA 文件中定义调用的函数参数和返回数据

public native String stringFromJNI();
public native int getFrameFromJNI(int[] data);
// Used to load the 'native-lib' library on application startup.
static {
    System.loadLibrary("native-lib");
}

在C++文件中写入这些函数的实现

extern "C" JNIEXPORT jstring JNICALL
Java_com_example_seziocr_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {

char pbuf[128];

pCap=new CapCocos();
int d=pCap->OpenVideo("/dev/video0");
sprintf(pbuf,"video0:%d",d);

LOGD("Hello World %d",d);
//return env->NewStringUTF(hello.c_str());
return env->NewStringUTF(pbuf);

}

注意 env 是链接 c++ 和 java 的数据格式转换的重要参数

还要研究怎么直接调用 so 的库不需要些源码