Add C/C++ codes into AS project

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1. create jni folder under main, jni and java folder are the same parent location
2. copy C and C++ files into jni folder
3. create Android.mk

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LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE    := gifflen   //lib name
LOCAL_SRC_FILES := gifflen.cpp  //src file
LOCAL_LDLIBS += -llog       // linked library
include $(BUILD_SHARED_LIBRARY)  //generate dynamic library

config build.gradle

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open the build.gradle under app folder

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add ndk module, the moduleName is mandatory, the ldLibs must set as above, some docs mentioned config ldLibs as ldLibs += "log", my AS will report error.

create java class for you c code

1. create java class

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  static{    
    System.loadLibrary("gifflen");
  }

means load the library

public native void Close();
public native int AddFrame(int[] pixels);

public native means declare the functions you want to use in java

2. change the jni name

find you pakage name in you java class

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now open the file which include the functions you want to invoke

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you'll find the JNIEXPORT name is "java_"+"package name"+"java class name"+"function name"
the picture is just the function declare, don't forget to change the real function name.

3. if you files include C and C++ files, don't forget add

#ifdef __cplusplus
#endif 

in you C files, or the AS will report error

Generate Libs

now, you can go to the jni folder, and generate libs

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find the libs in

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because I didn't config in build.gradle which platform I prefer, so ndk compiled all platforms libs

and next you could use jni gladly

how to add NDK in AS

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click the top button, and choose NDK and ok button. AS will download NDK automatically.
if done, you can find the ndk in "Android/sdk/ndk-bundle", and then export ndk-build PATH "export PATH=$PATH:/usr/local/bin:/Users/liut1/Library/Android/sdk/ndk-bundle"

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check out the ndk path in the local.properties of your AS project, if error, correct it, if miss, add it.