Android App with OpenCV and C++, Part 2

1. Add opencv to the workspace

File->Import..->Android->Existing Code into Workspace.  Locate the path and check "Copy projects into workspace"

2. Add opencv dependency to the project:

Right click on the project->properties->Android, click "Add", and add the opencv lib:

3. Add opencv support code:

Add declarations:

Mat mat;
private BaseLoaderCallback  mLoaderCallback;

Overload onResume():

@Override
public void onResume(){
    super.onResume();
    OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_9, this, mLoaderCallback);
}

Add initilization in onCreate(), and any matrices are to be created after opencv lib are laoded successfully:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mLoaderCallback = new BaseLoaderCallback(this) {
    
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
            case LoaderCallbackInterface.SUCCESS:
                Log.i("HelloWorld: ", "OpenCV loaded successfully");
                System.loadLibrary("HelloWorld");
                createOpencvMatrices();
                break;
            default:
               super.onManagerConnected(status);
            }
        }
    };
}
    
void createOpencvMatrices(){
    mat = new Mat();
    // other matrices to be created, ...
}

Add a test function:

 public native int test0(long matAddrDat); 

Edit file activity_main.xml in res->layout:

<TextView
    android:id="@+id/tvHello"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World" />

Declare TextView tvHello, and added this to onCreate:

tvHello = (TextView) findViewById(R.id.tvHello);

Add following after createOpencvMatrices();

createOpencvMatrices(); // matrix creation comes after loadLibrary
int out = test0(mat.getNativeObjAddr());  // test function
tvHello.setText("output from test0() = "+ out);

Edit HelloWorld.cpp:

......
JNIEXPORT int JNICALL Java_org_ski_helloworld_MainActivity_test0(JNIEnv*, jobject, jlong addrData)
{
    Mat& mat = *(Mat*)addrData;
    mat.create(1,3,CV_32F);
    Mat_<float> &tmp = (Mat_<float> &)mat;
    Mat_<float>::iterator it;
    int i=1;
    for (it =tmp.begin(); it!= tmp.end(); it++,i++)
        *it = i;

    int sum = 0;
    for (it = tmp.begin(); it!= tmp.end(); it++)
        sum += *it;
    return sum;
}
......

You should get "output from test0() = 6" after you launch the app. The zip file of the project: link.