DllNotFoundException in NDK Android app using Xamarin

Issue

I want to make an Android app that uses NDK with C++

I made a new Android App solution in Xamarin Studio called ndkTest. I added a folder jni, and in there added these files:

• Android.mk
• Application.mk
• my.h
• test.cpp

Here are the contents of each:

Android.mk :

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := ndkTest
LOCAL_SRC_FILES := test.cpp
LOCAL_STATIC_LIBRARIES := my

include $(BUILD_SHARED_LIBRARY)

Application.mk :

APP_ABI := armeabi-v7a
APP_STL := stlport_static

my.h :

#ifndef __MY_H__
#define __MY_H__

#define MY_CONST    1

#ifdef __cplusplus
extern "C"
#endif
short
my_func( short          my_param );

#endif /* __MY_H__ */

test.cpp:

// test.cpp
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <memory.h>

#include <iostream>
#include <fstream>
#include <vector>

#include "my.h"

#define SOME_CONST     2*MY_CONST
short  some_short;

#ifdef __cplusplus
extern "C"
{
#endif

static void static_func_0()
{
some_short = 0;
}

static void static_func_1()
{
some_short = 1;
}

#ifdef __cplusplus
}
#endif

static void static_print()
{
printf("static_print\n");
printf("some_short = %d\n", some_short);
}

extern "C" short getSomeShort()
{
printf("myExtern\n");
return some_short;
}

---

Here's where it gets interesting: I have ndk installed and properly configured. In the command line, I cd to project directory and run

ndk-build

And I get this error:

make.exe: *** No rule to make target [path to ndk]/sources/cxx-stl/stlport/test.cpp', needed byobj/local/armeabi/objs/ndkTest/test.o'. Stop.

That's weird, but whatever, I can specify the full path to test.cpp in Android.mk and it builds:

[armeabi] Compile++ thumb: ndkTest <= test.cpp
[armeabi] SharedLibrary : libndkTest.so
[armeabi] Install : libndkTest.so => libs/armeabi/libndkTest.so

So now I have the .so file. After adding this to top of MainActivity.cs : using System.Runtime.InteropServices; I added this:

[DllImport("libndkTest", EntryPoint="getSomeShort")]
static extern short getSomeShort();

And I added a call to that in OnCreate. I'm getting a DllNotFoundException. What am I missing?

Solution

I found a workaround:

In Xamarin Studio, go to Project Options, Build, Android Build, and in the Advanced tab, uncheck all the Supported ABIs except armeabi-v7a. For some reason, the app doesn't work on a Samsung S6 using arm64-v8a, even though it clearly should.

YMMV

Answered By - dstrube