A preliminary study on the use of ndk and JNI

References:

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

Create a C++ project

Understanding the CMakeList.txt file,

Set header files and add source files

#Set the header file to the current pathINCLUDE_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.cppv4l2Cocos.cpp )

Also calling Kuba in the library should be

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} )

Define the function parameters and return data in the JAVA file

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");}

Write the implementation of these functions in a C++ file

extern "C" JNIEXPORT jstring JNICALLJava_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);

}

Note that env is an important parameter for linking c++ and java data format conversion

Also study how to directly call the so library without some source code