Get Java Array From C++ Via Jni

So, I want to obtain resultNative from c++ but resultNative is in Java. can anybody please show me how to do that via JNI? I am not so familiar with c++ and have searched google f

Solution 1:

First you have to get a reference to the class providing the method. Let's say your class is called MyClass and it is in package p. You get the reference to the class like this:

// You get the JNIEnv* pointer when calling a native function.jclassmyClass= env->FindClass("p/MyClass");

Or if you have a reference to the java object then you can also use GetObjectClass:

jclass myClass = env->GetObjectClass(javaObject);

Then you have to get the ID of the method you'd like to call by providing the name of the method and a string describing the signature of the method.

"()[java/lang/String;" describes a method expecting no arguments and returning a stringarray.
jmethodID methodID = env->GetMethodID(myClass , "searchDatabase", "()[java/lang/String;");

Then you have to call the method with JNIEnv::CallObjectMethod, and here you have to pass the referenc to the java object.

jobjectarray strings = env->CallObjectMethod(javaObject, methodID);

Then you can get an element of the array with GetObjectArrayElement.

intindex = 0;
jstring string = env->GetObjectArrayElement(strings, index);

And then you can get the native string from it in various ways.

constchar* nativeChars = env->GetStringUTFChars(string, nullptr);

You can find more information about JNI here, and details about JNI type signatures here.

Solution 2:

I believe you could do it by passing back a jobjectArray.

int elements = 5;
jobjectArray returnArray = (jobjectArray)env->NewObjectArray(elements, env->FindClass("java/lang/string"), env->NewStringUTF(""));
for(int i = 0; i < elements; i++)
{
    charstr[12];
    sprintf(str, "%i", i);
    env->SetObjectArrayElment(returnArray, i, env->NewStringUTF(str));
}

return returnArray;

I've only done this with a byte array