Dependent DLL is not getting copied to the build output folder in Visual Studio

Question

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

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TLDR  Visual Studio 2019 may simply need a restart   I encountered this situation using projects based on Microsoft NET Sdk project    lt Project Sdk  Microsoft NET Sdk  gt    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  -

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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

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

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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

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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

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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   lt ProjectReference Include  quot Project B csproj quot  gt     lt Project gt  blah blah  lt  Project gt     lt Name gt Project B lt  Name gt     lt Private gt True lt  Private gt   lt  ProjectReference gt   I manually deleted the line  lt Private gt True lt  Private gt  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  quot Copy Local quot  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

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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  quot Private quot  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

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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

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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

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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

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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  gt  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

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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 lt Type gt  noop       gt              var dummy   typeof AbcDll AnyClass           noop dummy             This infomation actually costed me hours to figure out  so I thought I share it

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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

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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 lt Type gt  noop       gt               noop forcedType             The usage will be    assembly  ForceAssemblyReference typeof AbcDll AnyClass

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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

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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

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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

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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

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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

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

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