[c#] Dependent DLL is not getting copied to the build output folder in Visual Studio

I have a visual studio solution. I have many projects in the solution. There is one main project which acts as the start up and uses other projects. There is one project say "ProjectX". Its reference is added to main project. The ProjectX references another .NET dll (say abc.dll) that isn't part of the solution.

Now this abc.dll should be copied to bin/debug folder of main project, but it isn't getting copied there. Why is it not getting copied, any known reasons ?

Make sure that the dependent dll used by you does not have target .net framework higher than the target .net framework of your project's Application.

You can check this by selecting your project, then press ALT+ENTER, then select Application from left side and then select Target Framework of your project.

Suppose, dependent dll Target Framework = 4.0 and Application dll Target Framework = 3.5 then change this to 4.0

Thank you!

Other than the common ones above, I had a multi-project solution to publish. Apparently some files target different frameworks.

So my solution: Properties > Specific Version (False)

You could also check to make sure the DLLs you're looking for aren't included in the GAC. I believe Visual Studio is being smart about not copying those files if it already exists in the GAC on the build machine.

I recently ran in this situation where I'd been testing an SSIS package that needed assemblies to exist in the GAC. I'd since forgotten that and was wondering why those DLLs weren't coming out during a build.

To check what's in the GAC (from a Visual Studio Developer Command Prompt):

gacutil -l

Or output to a file to make it easier to read:

gacutil -l > output.txt
notepad.exe output.txt

To remove an assembly:

gacutil -u MyProjectAssemblyName

I should also note, that once I removed the files from the GAC they were correctly output in the \bin directory after a build (Even for assemblies that were not directly referenced in the root project). This was on Visual Studio 2013 Update 5.

You may set both the main project and ProjectX's build output path to the same folder, then you can get all the dlls you need in that folder.

If you right Click the referenced assembly, you will see a property called Copy Local. If Copy Local is set to true, then the assembly should be included in the bin. However, there seams to be a problem with Visual studio, that sometimes it does not include the referenced dll in the bin folder... this is the workaround that worked for me:

VS2019 V16.6.3

For me the problem was somehow the main .proj file ended up with an entry like this for the project whose DLL wasn't getting copied to the parent project bin folder:

<ProjectReference Include="Project B.csproj">
  <Project>{blah blah}</Project>
  <Name>Project B</Name>
  <Private>True</Private>
</ProjectReference>

I manually deleted the line <Private>True</Private> and the DLL was then copied to the main project bin folder on every build of the main project.

If you go to the reference of the problem project in the references folder of the main project, click it and view properties there is a "Copy Local" setting. The private tag equates to this setting, but for me for some reason changing copy local had no effect on the private tag in the .proj file.

Annoyingly I didn't change the copy local value for the reference, no idea how it got set that way and another day wasted tracking down a stupid problem with VS.

Thanks to all the other answers that helped zone me in on the cause.

HTH

Just a sidenote to Overlord Zurg's answer.

I've added the dummy reference this way, and it worked in Debug mode:

public class DummyClass
{
    private static void Dummy()
    {
        var dummy = typeof(AbcDll.AnyClass);
    }
}

But in Release mode, the dependent dll still did not get copied.
This worked however:

public class DummyClass
{
    private static void Dummy()
    {
        Action<Type> noop = _ => {};
        var dummy = typeof(AbcDll.AnyClass);
        noop(dummy);
    }
}

This infomation actually costed me hours to figure out, so I thought I share it.

In my case, it was the stupidest thing, caused by a default behavior of TFS/VS that I disagree with.

Since adding the dll as a reference to the main project did not work, I decided to add it as an "Existing Item", with Copy Local = Always. Even then the file was not there.

Turns out that, even though the file is present on the VS Solution and everything compiled both locally and on the server, VS/TFS did not add actually add the file to source control. It was not included on the "Pending Changes" at all. I had to manually go to the Source Control Explorer and explicitly click on the "Add items to folder" icon.

Stupid because I've been developing for 15 years in VS. I've run into this before, I just did not remember and somehow I missed it because everything still compiled because of the file being a regular reference, but the file that was added as Existing Item was not being copied because it did not exist on the source control server.

I hope this saves someone some time, since I lost 2 days of my life to this.

Yes, you'll need to set Copy Local to true. However, I'm pretty sure you'll also need to reference that assembly from the main project and set Copy Local to true as well - it doesn't just get copied from a dependent assembly.

You can get to the Copy Local property by clicking on the assembly under References and pressing F4.

This is a slight tweak on nvirth's example

internal class DummyClass
{
    private static void Dummy()
    {
        Noop(typeof(AbcDll.AnyClass));
    }
    private static void Noop(Type _) { }
}

NO NEED FOR DUMMY IN CODE
Just :

add a Reference to the Executeable Project

or/and ensure that the reference in the executeable project has "Copy Local" set to TRUE (which was my "fault") is seems that this "overwrote" the setting in the base referenced library-project...

Ran into this same issue. Background info: before building, I had added a new Project X to the solution. Project Y depended on Project X and Project A, B, C depended on Project Y.

Build errors were that Project A, B, C, Y, and X dlls could not be found.

Root cause was that newly created Project X targeted .NET 4.5 while the rest of the solution projects targeted .NET 4.5.1. Project X didn't build causing the rest of the Projects to not build either.

Make sure any newly added Projects target the same .NET version as the rest of the solution.

Not sure if this helps but for me, many times I reference a DLL (which automatically adds it to the bin folder of course). However that DLL might need additional DLLs (depending on what functions I'm using). I do NOT want to reference those in my Project because they just simply need to end up in the same folder as the DLL I am actually using.

I accomplish this in Visual Studio by "Adding an existing file". You should be able to add it anywhere except the Add_data folder. personally I just add it to the root.

Then change the properties of that file to ...

Build Action = None (having this set to something like Content actually copies the "root" version to the root, plus a copy in the Bin).

Copy to output folder = Copy if Newer (Basically puts it in the BIN folder only if it is missing, but doesn't do it after that)

When I publish.. my added DLL's only exists in the BIN folder and nowhere else in the Publish location (which is what I want).

It looks slick when you make it an assembly attribute

[AttributeUsage(AttributeTargets.Assembly)]
public class ForceAssemblyReference: Attribute
{        
    public ForceAssemblyReference(Type forcedType)
    {
        //not sure if these two lines are required since 
        //the type is passed to constructor as parameter, 
        //thus effectively being used
        Action<Type> noop = _ => { };
        noop(forcedType);
    }
}

The usage will be:

[assembly: ForceAssemblyReference(typeof(AbcDll.AnyClass))]

Issue:

Encountered with a similar issue for a NuGet package DLL (Newtonsoft.json.dll) where the build output doesn't include the referenced DLL. But the compilation goes thru fine.

Fix:

Go through your projects in a text editor and look for references with "Private" tags in them. Like True or False. “Private” is a synonym for “Copy Local.” Somewhere in the actions, MSBuild is taking to locate dependencies, it’s finding your dependency somewhere else and deciding not to copy it.

So, go through each .csproj/.vbproj file and remove the tags manually. Rebuild, and everything works in both Visual Studio and MSBuild. Once you’ve got that working, you can go back in and update the to where you think they need to be.

Reference:

https://www.paraesthesia.com/archive/2008/02/13/what-to-do-if-copy-local-works-in-vs-but.aspx/

TLDR; Visual Studio 2019 may simply need a restart.

I encountered this situation using projects based on Microsoft.NET.Sdk project.

<Project Sdk="Microsoft.NET.Sdk">

Specifically:

• Project1: targets .netstandard2.1
  • references Microsoft.Extensions.Logging.Console via Nuget
• Project2: targets .netstandard2.1
  • references Project1 via a Project reference
• Project2Tests: targets .netcoreapp3.1
  • references Project2 via a Project reference

At test execution, I received the error messaging indicating that Microsoft.Extensions.Logging.Console could not be found, and it was indeed not in the output directory.

I decided to work around the issue by adding Microsoft.Extensions.Logging.Console to Project2, only to discover that Visual Studio's Nuget Manager did not list Microsoft.Extensions.Logging.Console as installed in Project1, despite it's presence in the Project1.csproj file.

A simple shut down and restart of Visual Studio resolved the problem without the need to add an extra reference. Perhaps this will save someone 45 minutes of lost productivity :-)

I found that if ProjectX referenced the abc.dll but didn't directly use any of the types DEFINED in abc.dll, then abc.dll would NOT be copied to the main output folder. (It would be copied to the ProjectX output folder, to make it extra-confusing.)

So, if you're not explicitly using any of the types from abc.dll anywhere in ProjectX, then put a dummy declaration somewhere in one of the files in ProjectX.

AbcDll.AnyClass dummy006; // this will be enough to cause the DLL to be copied

You don't need to do this for every class -- just once will be enough to make the DLL copy and everything work as expected.

Addendum: Note that this may work for debug mode, but NOT for release. See @nvirth's answer for details.

Add the DLL as an existing item to one of the projects and it should be sorted

I would do add it to Postbuild events to copy necessary libraries to the output directories. Something like XCopy pathtolibraries targetdirectory

You can find them on project properties -> Build Events.