如何通过一个ArrayList的＆LT;＆垫GT;从Java到OpenCV的机端（NDK）为Android [英] How to pass a ArrayList<Mat> from Java to native side(NDK) in opencv for android

问题描述

在Java方面我有

列表＆LT;＆垫GT; arystrdimages =新的ArrayList＆LT;＆垫GT;（）;


随后从在外部目录的文件夹读出的图像被添加到列表

 的（文件f：strdimgs）
        {        垫tempimg = Highgui.imread（f.getAbsolutePath（），CvType.CV_8UC1）;        arystrdimages.add（tempimg）;
        }
 

在本机JNI边我想通过它的引用来访问arystrdimages。

对于单个垫目标，我们可以通过调用 getNativeObjAddr 的方法，即在一个垫opencv4android示例对象在本机端的访问做如下图所示<做到这一点/ p>

Java的

 私人垫mRgba;
 

调用本机端

  CallNative（mRgba.getNativeObjAddr（））;
 

在本机端

  JNIEXPORT无效JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_CallNative（JNIEnv的*，jobject，jlong​​ addrRgba1）{ 垫＆安培; mRgb = *（*垫）addrRgba1;}
 

如何为列表＆LT做到这一点;垫＆GT; 对象

  

编辑：您的建议的解决方案的实施

Java端

  INT elems = arystrdimages.size（）;
            Log.v（Matobjdata，Matobject数读=+ elems）;
            //Log.v(\"Matobjdata，从天然=+ ANS）;
            长[] = tempobjadr新长[elems]
            的for（int i = 0; I＆LT; elems;我++）
            {
                垫tempaddr = arystrdimages.elementAt（I）
                tempobjadr [I] = tempaddr.getNativeObjAddr（）;
            }            Log.v（Matobjdata，addresselementsinlong arrray =+ tempobjadr.length）;
            INT ANS = TrainDescriptors（tempobjadr）; //调用本地函数
            Log.v（Matobjdata，从天然=+ ANS）;
 

本机端

  JNIEXPORT jint JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_TrainDescriptors（JNIEnv的* ENV，jobject trainobject，jlong​​Array traindataaddr）
{矢量＆lt;＆垫GT; trainimgs;
jsize a_len = env-＆GT; GetArrayLength（traindataaddr）;
jlong​​ * traindata = env-＆GT; GetLongArrayElements（traindataaddr，0）;对于（INT K = 0; K＆LT; a_len; k ++）
{
    垫＆安培; newimage = *（*垫）traindata [K];
    trainimgs.push_back（newimage）;
}
//做图像所需要的操作;
env-＆GT; ReleaseLongArrayElements（traindataaddr，traindata，0）;    返回a_len;
}
 

解决方案

您可以建立在Java中，长值数组（getNativeObjAddr（）的所有垫的结果），并调用传递数组本机的功能。

在JNI，可以用GetArrayLength和GetLongArrayElements（返回jlong​​ *的第一个元素）访问所有的长期价值。

使用ReleaseLongArrayElements时完成的。

In Java side i have

List<Mat> arystrdimages = new ArrayList<Mat>();

subsequently the images read from a folder in external directory are added into the list

for(File f:strdimgs)
        {

        Mat tempimg = Highgui.imread(f.getAbsolutePath(),CvType.CV_8UC1);

        arystrdimages.add(tempimg );
        }

In Native jni side i want to access arystrdimages by its reference.

For a single mat object, we can do it by calling getNativeObjAddr method, i.e in opencv4android examples for a Mat object the accessing in native side is done as shown below

Java

private Mat mRgba;

call to native side

CallNative(mRgba.getNativeObjAddr());

In Native side

    JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_CallNative(JNIEnv*, jobject,  jlong addrRgba1){

 Mat& mRgb = *(Mat*)addrRgba1;

}

How to do this for List<Mat> objects?.

EDIT: Implementation of your suggested solution

Java side

int elems=  arystrdimages.size();
            Log.v("Matobjdata", "number of Matobject read = " + elems);
            //Log.v("Matobjdata", "from native = " + ans);
            long[] tempobjadr = new long[elems]; 
            for (int i=0;i<elems;i++)
            {
                Mat tempaddr=arystrdimages.elementAt(i);
                tempobjadr[i]=  tempaddr.getNativeObjAddr();
            }

            Log.v("Matobjdata", "addresselementsinlong arrray = " + tempobjadr.length);
            int ans = TrainDescriptors(tempobjadr);//call to native function
            Log.v("Matobjdata", "from native = " + ans);

Native side

JNIEXPORT jint JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_TrainDescriptors(JNIEnv * env, jobject trainobject,jlongArray traindataaddr)
{

vector<Mat> trainimgs;
jsize a_len = env->GetArrayLength(traindataaddr);
jlong *traindata = env->GetLongArrayElements(traindataaddr,0);

for(int k=0;k<a_len;k++)
{
    Mat & newimage=*(Mat*)traindata[k];
    trainimgs.push_back(newimage);
}
// do the required manipulation on the images; 
env->ReleaseLongArrayElements(traindataaddr,traindata,0);

    return a_len;


}

解决方案

You could build, in Java, an array of long values (getNativeObjAddr() results for all the Mat) and call a native function passing the array.

In JNI, you could access all the long values with GetArrayLength and GetLongArrayElements (which returns a jlong* to the first element).

Use ReleaseLongArrayElements when done.

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