How to add external native dependency dll?

Question

I have two projects. First is a Windows Forms Application project and second is a class library project. Сlass library project works with FANN. Windows Forms is Startup Project.

I should have Fann.Net.dll and fanndoubleMT.dll to work with the FANN. I downloaded these libraries and put their in a folder lib, located in the root of the solution.

I added Fann.Net.dll as external dll to the class library project. I compiled the project. I got an error that says "Unable to load DLL 'fanndoubleMT.dll'. I fixed this error by adding fanndoubleMT.dll to the folder Windows_Forms_Application\bin\Debug.

I think this is a terrible solution to the problem, because I use git, and every time you need to transfer dll to this folder on the new workplace.

Sincerely, Denis.

Answer 1

You may try this:

1. Add/Existing Item, instead of Add Reference.
2. Use Add As Link.
3. Make sure the item is to be copied in build folder. In the property of the library in VS, set Build Action to Content and Copy to Output Directory to Copy if Newer.
4. Done. Rebuild and test.

Suggested in the link http://social.msdn.microsoft.com/Forums/en-US/1b1b316a-8648-4243-a651-84de51fd2508/reference-native-dll-from-managed-c-project?forum=vssmartdevicesvbcs.

Answer 2

You can add the native dll as a linked item, and use "Copy if newer".
The problem with native dlls, is that sometimes you'll want to use different dlls according to the project's configuration (Debug/Release or platform).

You can edit the project's .csproj and link the native dll conditionally:

 <ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|Win32' ">
    <Content Include="..\..\..\..\..\bin\Win32\Release\fanndoubleMT.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
 </ItemGroup>   
 <ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|Win32' ">
    <Content Include="..\..\..\..\..\bin\Win32\Debug\fanndoubleMT_d.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
  </ItemGroup>
  <ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|x64' ">
    <Content Include="..\..\..\..\..\bin\x64\Debug\fanndoubleMT_d.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
  </ItemGroup>
  <ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|x64' ">
    <Content Include="..\..\..\..\..\bin\x64\Release\fanndoubleMT.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
  </ItemGroup>

Note the copy option is set to PreserveNewest which means "copy if newer".

Answer 3

The above solution written by liang works only for flat project structure! You may want to organize all your DLLs in your solution into one folder named "Dependecies". But beware that files are copied relatively to project structure in the Solution Explorer. (tested with Visual Studio 2015)

1. Create Folder Dependencies in your Solution Explorer
2. Add/Existing Item, instead of Add Reference.
3. Use Add As Link.
4. In the property of the library in VS, set Build Action to Content and Copy to Output Directory to Copy if Newer.

Now you should have following Solution Explorer structure:

Your Project
- class1.cs
- Dependencies\Fann.Net.dll
- Dependencies\fanndoubleMT.dll

Add postbuild step:

xcopy "$(TargetDir)\Dependencies" "$(TargetDir)"  /s /e /h /Y

This solution combining adding files to project and creating post build step has following advantages:

• Project is well organized
• No need to modify post build step if someone add a new dependency to solution explorer later,
• If you use subversion, it will reset readonly flag of locked file in repository