Unity Native C++ Plug-in for Android

Question

I am making a native plug-in for Android written in C++ and packaged in a shared library for the Unity Game Engine. However, I'm getting an EntryPointNotFoundException with even the default native-lib.cpp generated by Android Studio.

#include <jni.h>
#include <string>

extern "C" JNIEXPORT jstring JNICALL Java_com_example_willgauthier_stublibrary_MainActivity_stringFromJNI(
    JNIEnv *env,
    jobject /* this */) {
std::string hello = "Hello from C++";
return env->NewStringUTF(hello.c_str());
}

In Android Studio I built the project. Then in Unity I made the folder structure Assets/Plugins/Android/libs and copied over the shared libnative-lib.so libraries armeabi-v7a and x86 .

I attached this script to an empty game object:

using System;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.UI;

public class LibLoadTest : MonoBehaviour
{
    public Text debugText;

    [DllImport("native-lib")]
    private static extern string stringFromJNI();

    private void Start()
    {
        try
        {
             debugText.text = stringFromJNI();
        }
        catch(Exception exception)
        {
            debugText.text = exception.ToString();
        }
    }
}

My debugText shows "System.EntryPointNotFoundException: stringFromJNI at (wrapper managed-to-native) LibLoadTest::stringFromJNI() at LibLoadTest.Start() [0x00000] in :0" instead of "Hello from C++".

Does anyone know how to successfully use a native plug-in shared library for Android in Unity and where I'm going wrong in my process? Thanks.

Answer 1

I figured out the issue thanks to Bonfire-Boy on the Unity Answers forums: the name of the function I should have been trying to import was Java_com_example_willgauthier_stublibrary_MainActivity_stringFromJNI , not just stringFromJNI . I incorrectly assumed that because the long name was auto-generated and included the package (not sure that's the correct term) structure, that it could be ignored. Deleting everything before stringFromJNI in the library function definition worked, though.