How to add JNI (native C / C ++ code) to an existing Android Studio project

Since Android Studio 3.1 it is possible in a simple way:

1. Create a folder cpp

inside app\src\main

.

2. Create a file <YOUR_FILE_NAME>.cpp

folder app\src\main\cpp

(for example native-lib.cpp).

3. Add the file CMakeLists.txt

to the folder app

.

This library file name should contain the file path .cpp

and some other parameters, for example (from a new blank Android Studio Project with C ++ support):

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# 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).
             src/main/cpp/native-lib.cpp )
                          ^^^^^^^^^^^^^^
                          YOUR_CPP_FILE_NAME

# 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.
                       native-lib

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

      

        
        
        
      

    

4. Add to build.gradle (module application) a tag externalNativeBuild

with a link to CMakeLists.txt

the section android

:

android {
    compileSdkVersion 26
    defaultConfig {
        ...
    }
    buildTypes {
        ...
    }
    externalNativeBuild {               <--- these lines should be added
        cmake {                         <--- these lines should be added
            path "CMakeLists.txt"       <--- these lines should be added
        }                               <--- these lines should be added
    }                                   <--- these lines should be added
}

      

        
        
        
      

    

5. Add to build.gradle (module application) a tag externalNativeBuild

with a tag cmake

in the section defaultConfig

:

...
defaultConfig {
    applicationId "<YOUR_APP_ID>"
    minSdkVersion 26
    targetSdkVersion 26
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"


    externalNativeBuild {   <--- these lines should be added
        cmake {             <--- these lines should be added
            cppFlags ""     <--- these lines should be added
        }                   <--- these lines should be added
    }                       <--- these lines should be added
}
...

      

        
        
        
      

    

(example of a "base" file build.gradle

also available in a new, empty Android Studio project with C ++ support)

6. Resync Project with Gradle files

By clicking Sync Project on the toolbar. NB! In Android Studio 3.3, this is an icon .

Also, take a look at the official tutorial .