DllImport - DllNotFoundException with android.so

Question

This is the first time I'm trying to create a C ++ library for Android / iOS.

I am using Visual Studio 2015 - Xamarin.

First I created a project: Visual C ++ -> Cross Platform -> Shared Library. In the guest library I created 2 files.

SayHello.h:

#pragma once #include <string.h> class SayHello { public: SayHello(); ~SayHello(); static char* Hello(); }; 

SayHello.cpp:

 #include "SayHello.h" extern "C" { SayHello::SayHello(){} SayHello::~SayHello(){} char * SayHello::Hello() { return "Hello !"; } } 

Then I generated the libSayHello.so file and created an Android project with xamarin to try to call the hello function. There is my MainActivity.cs:

 [DllImport("libSayHello.so")] static extern String Hello(); protected override void OnCreate(Bundle bundle) { // I paste only my added code : String hello = Hello(); Toast.MakeText(this.ApplicationContext, hello, ToastLength.Long); } 

I have done all the steps in this tutorial , but I have an exception:

System.DllNotFoundException: libSayHello.so

I was looking for this, but I have to be so noob because I did not find anything. How to use my libSayHello.so ?

EDIT:

There is my libSayHello.so with 7zip:

And my project:

Answer 1

I think this will be the best sample for you.

All this works as follows:

• Android supports 7 processor architectures.

  But Xamarin supports 5 of them. Therefore, in the settings of your Xamarin.Android project, check which architectures you will support:

  [Xamarin.Droid.project]->[Properties]->[Android Options]->[Advanced]->[Supported architectures]

Check which arches are needed for your project. Accordingly, your shared library should be compiled for these arches. And you should put your shared libraries in the Xamarin.Droid.project lib folder:

2. To see them in Solution Explorer, you must mention them in your Xamarin.Android .CSPROJ project.

   Add the following groups of elements there:

   <ItemGroup> <AndroidNativeLibrary Include="lib\{ARCH}\libCLib.so"> <Abi>{ARCH}</Abi> <CopyToOutputDirectory>Always</CopyToOutputDirectory> </AndroidNativeLibrary> </ItemGroup>

   {ARCH} could be: armeabi , armeabi-v7a , arm64-v8a , x86 x86_64 .

3. Now you can put DllImport in your code:

    [DllImport("libCLib", EntryPoint = "clib_add")] public static extern int Add(int left, int right); 

   I think you should say about the entry point because I had runtime errors without this System.EntryPointNotFoundException statement .

   And don't forget to add the following code:

   using System.Runtime.InteropServices;

Answer 2

• Confirm that the library is placed in the "/ lib / {arch} /" folder.
• Try [DllImport ("SayHello")]. the engine can automatically add "lib" and ".so".