如何为 jni C++ 函数传递 ArrayList<Point>？

Question

我正在 Java 使用 Android jni C++ 做一个项目。我在 C++ 中有一个具有以下参数的函数：

C++ 函数： void rectify (vector <Point2f> & corners, Mat & img) {...}

在 JAVA 中，呼叫将是：

Mat image = Highgui.imread("img.png");
List <MatOfPoint> cornners =  new ArrayList<MatOfPoint>();;
Point b = new Point (real_x2, real_y2);
MatOfPoint ma = new MatOfPoint (b);
cornners.add(ma);
rectfy(image.getNativeObjAddr(), cornners)

public native void rectfy(long mat, "??" matofpoint);

有了这个，我想知道函数 C++ jni:

JNIEXPORT void JNICALL Java_ImageProcessingActivity_rectfy (JNIEnv * jobject, ?? cornners, inputMatAddress jlong)

Answer 1

如果我对你的理解正确，你想做的是将一堆点从 Java 传递给 C++，那么我认为这大致就是你要找的东西：

#include <vector>
#include <jni.h>

class Point2f {
public:
    double x;
    double y;
    Point2f(double x, double y) : x(x), y(y) {}
};

extern "C" JNIEXPORT void JNICALL Java_com_example_ImageProcessingActivity_transferPointsToNative(JNIEnv* env, jobject self, jobject input) {
    jclass alCls = env->FindClass("java/util/ArrayList");
    jclass ptCls = env->FindClass("java/awt/Point");

    if (alCls == nullptr || ptCls == nullptr) {
        return;
    }

    jmethodID alGetId  = env->GetMethodID(alCls, "get", "(I)Ljava/lang/Object;");
    jmethodID alSizeId = env->GetMethodID(alCls, "size", "()I");
    jmethodID ptGetXId = env->GetMethodID(ptCls, "getX", "()D");
    jmethodID ptGetYId = env->GetMethodID(ptCls, "getY", "()D");

    if (alGetId == nullptr || alSizeId == nullptr || ptGetXId == nullptr || ptGetYId == nullptr) {
        env->DeleteLocalRef(alCls);
        env->DeleteLocalRef(ptCls);
        return;
    }

    int pointCount = static_cast<int>(env->CallIntMethod(input, alSizeId));

    if (pointCount < 1) {
        env->DeleteLocalRef(alCls);
        env->DeleteLocalRef(ptCls);
        return;
    }

    std::vector<Point2f> points;
    points.reserve(pointCount);
    double x, y;

    for (int i = 0; i < pointCount; ++i) {
        jobject point = env->CallObjectMethod(input, alGetId, i);
        x = static_cast<double>(env->CallDoubleMethod(point, ptGetXId));
        y = static_cast<double>(env->CallDoubleMethod(point, ptGetYId));
        env->DeleteLocalRef(point);

        points.push_back(Point2f(x, y));
    }

    env->DeleteLocalRef(alCls);
    env->DeleteLocalRef(ptCls);
}

在Java中有相应的方法声明：

private native void transferPointsToNative(ArrayList<Point> input);

如何为 jni C++ 函数传递 ArrayList<Point>？

How to pass a ArrayList<Point> for a jni C++ function?

c++

java

java-native-interface

android

opencv