安卓如何在java中调用nativelib的对象

Question

我正在做一个文档扫描仪。我正在使用opencv进行图像处理。在摄影机视图中，我在最大轮廓上包围矩形。正确地检测最大轮廓。现在我只想捕获用本机lib编写的boudingRect。cpp。所以我想要java类中本机库的对象。帮我弄到那个

本机库。cpp

extern "C"
JNIEXPORT void JNICALL
Java_prisca_ctest_OpenCvCamera_doWithMat(JNIEnv *env, jobject instance, jlong matAddrGr,
                                     jlong matAddrRgba) {
try {
    Mat &image = *(Mat *) matAddrRgba;
    Rect bounding_rect;

    Mat thr(image.rows, image.cols, CV_8UC1);
    cvtColor(image, thr, CV_BGR2GRAY); //Convert to gray
    threshold(thr, thr, 150, 255, THRESH_BINARY + THRESH_OTSU); //Threshold the gray

    vector<vector<Point> > contours; // Vector for storing contour
    vector<Vec4i> hierarchy;
    findContours(thr, contours, hierarchy, CV_RETR_CCOMP,
                 CV_CHAIN_APPROX_SIMPLE); // Find the contours in the image
    sort(contours.begin(), contours.end(),
         compareContourAreas);            //Store the index of largest contour
    bounding_rect = boundingRect((const _InputArray &) contours[0]);

rectangle(image, bounding_rect, Scalar(250, 250, 250) , 5);
} catch (int a) {

}
}

活动

 protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.cam);
    mOpenCvCameraView = (JavaCameraView) findViewById(R.id.tutorial1_activity_java_surface_view);
    mOpenCvCameraView.setVisibility(View.VISIBLE);

    mOpenCvCameraView.setCvCameraViewListener(this);
    btnCapture = (Button) findViewById(R.id.btnCapture);
    btnCapture.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            String timestamp = new SimpleDateFormat("ddMMyyyy_HHmmss", Locale.US).format(new Date());
            File imgFolder = new File(FILE_LOCATION);
            imgFolder.mkdir();
            File image = new File(imgFolder, "Scan" + timestamp + ".jpg");
            String fileName = FILE_LOCATION +
                    "/Scan" + timestamp + ".jpg";
            Toast.makeText(OpenCvCamera.this, image + " saved", Toast.LENGTH_SHORT).show();
            Imgcodecs.imwrite(fileName, mRgba);
        }
    }) ;
}

@Override
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
    // input frame has RGBA format
    mRgba = inputFrame.rgba();
    mGray = inputFrame.gray();
    doWithMat(mGray.getNativeObjAddr(), mRgba.getNativeObjAddr());
    return mRgba;

}

我应该在Imgcodecs上面添加什么。imwrite（文件名，mRgba）裁剪矩阵并仅保存boundingRect部分

Answer 1

假设您想调用本机JNI方法Java_prisca_ctest_OpenCvCamera_doWithMat

首先，要从Java端调用这个方法，需要声明它。要声明它，您需要了解该方法的名称，它为您提供了所需的一切：

1. Java\u prisca\u ctest\u OpenCvCamera\u doWithMat：这意味着这将由Java执行

2. Java\ustrong>prisca\u ctest\u OpenCvCamera\u doWithMat：这部分是类的包

3. Java_prisca_ctest_strong>OpenCvCamera\u doWithMat：这部分是Java类的名称

4. Java_prisca_ctest_OpenCvCamera_doWithMat：这部分是方法的名称

考虑到这一点，我们需要知道参数。在这种情况下很容易：两个jlong参数转换为Java long

创建一个OpenCvCamera.java类，并将其放入其中：

package prisca.ctest; // This part might actually be ctest.prisca, not sure

public class OpenCvCamera {
    public static native void doWithMat(long matAddrGr, long matAddrRgba);
}

现在可以通过导入类并调用OpenCvCamera.doWithMat(long, long)来调用该方法。请注意，这可能不是100%正确，我对JNI不太在行（尤其是在脑海中写下它），但这应该让你开始：）