TwoWayJNI

The project is POC of using JNI for Android NDK. It consists in 3 modules:

• Calling C++ function from Kotlin
• Calling Kotlin function from C++
• Calling Kotlin function from Kotlin, then calling C++ function from another C++ Lib then calling Kotlin function again

On Mac(or any other OS) install the NDK and execute the following command lines:

export ANDROID_SDK=/Users/mariusduna/Library/Android/sdk

export PATH=$PATH:$ ANDROID_SDK/tools:$ANDROID_SDK/platform-tools

export ANDROID_NDK=/Users/mariusduna/Library/Android/sdk/ndk/24.0.8215888

export PATH=$PATH:$ANDROID_SDK/tools:$ANDROID_SDK/platform-tools:$ANDROID_NDK

ndk-build - is needed for for building the native libraries

Steps:

1. Execute #Build #1 section from Android.mk file, leave #Build #2 section commented out
2. Copy the output from /jni folder to /jniLibs folder
3. Execute #Build #2 section from Android.mk file, leave #Build #1 section commented out
4. Copy the output from /jni folder to /jniLibs folder
5. Run the Android app

Notes:

• On step 1 the lib.so lib is generated and includes also static reference to cujo.so lib
• On step 2 only shared lib is generated - used to show how JNI works in both directions

Also:

1. From the MainActivity the direct JNI calls from and to c library are made
2. From the SpeedActivity calls from c to another c library and back to Kotlin are made. All calls can be triggered in both directions.