There’s a missing file of libopencv_java4.so in your subfolders under JNILIBS folder. Assume that you want to support different platforms, this file can be put in each of the subfolders. This will solve the problem.

I’m trying to do basic usage of OpenCv in android.

This is my main activity on create:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    OpenCVLoader.initDebug();
    Mat image_mat = new Mat();

It fails:

No implementation found for long org.opencv.core.Mat.n_Mat() (tried Java_org_opencv_core_Mat_n_1Mat and Java_org_opencv_core_Mat_n_1Mat__)

I’ve tried multiple HOW-TO opencv + android tutorials. It doesn’t work for me.

I’ve downloaded opencv-4.4.0-android-sdk.
I’ve added the sdk/java directory as module dependency (after rename to the name “opencv”):

This is the start of my app build gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "org.tensorflow.lite.examples.classification"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    aaptOptions {
        noCompress "tflite"
    }
    compileOptions {
        sourceCompatibility = '1.8'
        targetCompatibility = '1.8'
    }
    lintOptions {
        abortOnError false
    }
}

And this is my opencv module build gradle:

//apply plugin: 'com.android.application'
apply plugin: 'com.android.library'

android {
    compileSdkVersion 28
//    buildToolsVersion "29.0.2"

    defaultConfig {
//        applicationId "org.opencv"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
        }
    }
}

That’s my project structure (as you can see, added jnilibs under main):

I’ve also tried to add this:

private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
    @Override
    public void onManagerConnected(int status) {
        switch (status) {
            case LoaderCallbackInterface.SUCCESS:
            {
                Log.i(TAG, "OpenCV loaded successfully");
            } break;
            default:
            {
                super.onManagerConnected(status);
            } break;
        }
    }
};

public void onResume()
{
    super.onResume();
    if (!OpenCVLoader.initDebug()) {
        Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initialization");
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, mLoaderCallback);
    } else {
        Log.d(TAG, "OpenCV library found inside package. Using it!");
        mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
    }
}

And then on onCreate():

if (!OpenCVLoader.initDebug()) {
    Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initialization");
    OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, mLoaderCallback);
}

It writes:

I/TFLiteExample: OpenCV loaded successfully
/TFLiteExample: Internal OpenCV library not found. Using OpenCV Manager for initialization

What am I missing?
Thanks