Accessing C++ code in Apache Cordova for Android

I am developing an app to target Windows 10 and Android using Apache Cordova in Visual Studio 2015. The backend logic will be contained in a c++ project which will hopefully be compiled into a .so or .dll depending on the platform.

I have done some research into Cordova plugins for android but there haven't been any good tutorials. What specifically do I need to do (on the c++ as well as javascript sides) to connect the two code bases?

After some more research and and a lot of dead ends, I was able to get my C++ code to run on Cordova. I'm replying here to document some of my problems and give some good resources for others attempting a similar thing.

Cordova plugin development

A good tutorial that explains each part of the plugin better than the official documentation: https://blogs.oracle.com/mobile/entry/introduction_to_custom_cordova_plugin

My biggest problem with this part of development was that the Cordova plugin removal in VS 2015 does a crap job and sometimes looks for files in the wrong places. Be wary of this if you need to change your plugin xml file.

Communicating with C++

I used VS to build the code into a .so shared library (new project --> android shared library). Make sure that you build it in ARM, not x86 or another configuration. Place the .so file in /libs/armeabi so the .java file can find it using the loadLibrary() method.

Here is my .java file for loading and calling a function from the library:

package com.example.plugin.cpp;

import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;

import org.apache.cordova.CordovaArgs;
import org.apache.cordova.CallbackContext;
import org.apache.cordova.CordovaPlugin;
import org.apache.cordova.CordovaWebView;
import org.apache.cordova.CordovaInterface;
import org.apache.cordova.PluginResult;

import org.json.JSONObject;
import org.json.JSONArray;
import org.json.JSONException;

public class Cpp extends CordovaPlugin {

    public static final String ACTION_SEVEN = "seven"; 

    public Cpp() { }

    @Override
    public boolean execute(String action, JSONArray args, CallbackContext callbackContext) {

        if (ACTION_SEVEN.equals(action)) {
            alert("Message from Java", "Grabbed the number " + get7() + " from C++", "dismiss", callbackContext);
            callbackContext.success();
            return true;
        }
        return false;
    }

    private synchronized void alert(final String title, 
                              final String message, 
                              final String buttonLabel, 
                              final CallbackContext callbackContext) {
        new AlertDialog.Builder(cordova.getActivity())
            .setTitle(title)
            .setMessage(message)
            .setCancelable(false)
            .setNeutralButton(buttonLabel, new AlertDialog.OnClickListener() {
                public void onClick(DialogInterface dialogInterface, int which) {
                    dialogInterface.dismiss();
                    callbackContext.sendPluginResult(new PluginResult(PluginResult.Status.OK, 0));
                }
            })
            .create()
            .show();
    }

    public native int get7();

    static {
        System.loadLibrary("CppLibrary");
    }
}

And here is the corresponding C++ code:

CppLibrary.cpp:

#include "CppLibrary.h"

extern "C" {

    JNIEXPORT int JNICALL Java_org_example_plugin_cpp_Cpp_get7(JNIEnv* env, jobject thiz)
    {
        return 7;
    }

}

Cpp.h:

#pragma once

extern "C" {
    JNIEXPORT int JNICALL Java_org_example_plugin_cpp_Cpp_get7(JNIEnv* env, jobject thiz);
}

C-side implementation resources:

http://developer.android.com/ndk/samples/sample_hellojni.html#ci

http://developer.android.com/training/articles/perf-jni.html#faq_ULE