JNI - how to use multiple Jni wrapper instances with different fields?

Question

background

I have an android project that uses JNI (using NDK) to code in both Java and C/C++.

I\'ve created a Jni java wrapper on the java side that will do a

Answer 1

I've found a possible solution (link here), to either use a jlong or jobject to be a handle (or pointer, if you wish) to the object that was created on the JNI side.

people said it's better to use a jobject as ByteBuffer instead of jlong for better compatibility.

the solution is :

Java side:

private native ByteBuffer init();
private native void foo(ByteBuffer handle);

JNI side:

/**a class to hold the fields*/
class FieldsHolder
  {
  ... //private fields, for each instance
  }

creating the JNI object and sending to java side:

JNIEXPORT jobject JNICALL ...init(JNIEnv * env, jobject obj)
  {
  FieldsHolder* myClass= new FieldsHolder();
  ... //prepare fields of the class
  return env->NewDirectByteBuffer(myClass, 0);
  }

re-using the JNI object :

JNIEXPORT void JNICALL ...foo(JNIEnv * env, jobject obj, jobject handle)
  {
  FieldsHolder* myClass= (FieldsHolder*) env->GetDirectBufferAddress(handle);
  //now we can access the fields again.
  }