How to add folder to assembly search path at runtime in .NET?

user_129150 0
Viewed 108507

My DLLs are loaded by a third-party application, which we can not customize. My assemblies have to be located in their own folder. I can not put them into GAC (my application has a requirement to be deployed using XCOPY). When the root DLL tries to load resource or type from another DLL (in the same folder), the loading fails (FileNotFound). Is it possible to add the folder where my DLLs are located to the assembly search path programmatically (from the root DLL)? I am not allowed to change the configuration files of the application.

path search assemblies .net
8 Answers

I've used @Mattias S' solution. If you actually want to resolve dependencies from the same folder - you should try using Requesting assembly location, as shown below. args.RequestingAssembly should be checked for nullity.

System.AppDomain.CurrentDomain.AssemblyResolve += (s, args) =>
{
    var loadedAssembly = System.AppDomain.CurrentDomain.GetAssemblies().Where(a => a.FullName == args.Name).FirstOrDefault();
    if(loadedAssembly != null)
    {
        return loadedAssembly;
    }

    if (args.RequestingAssembly == null) return null;

    string folderPath = Path.GetDirectoryName(args.RequestingAssembly.Location);
    string rawAssemblyPath = Path.Combine(folderPath, new System.Reflection.AssemblyName(args.Name).Name);

    string assemblyPath = rawAssemblyPath + ".dll";

    if (!File.Exists(assemblyPath))
    {
        assemblyPath = rawAssemblyPath + ".exe";
        if (!File.Exists(assemblyPath)) return null;
    } 

    var assembly = System.Reflection.Assembly.LoadFrom(assemblyPath);
    return assembly;
 };
user_11513920

I came here from another (marked duplicate) question about adding the probing tag to the App.Config file.

I want to add a sidenote to this - Visual studio had already generated an App.config file, however adding the probing tag to the pregenerated runtime tag did not work! you need a seperate runtime tag with the probing tag included. In short, your App.Config should look like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
    </startup>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Text.Encoding.CodePages" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-4.1.1.0" newVersion="4.1.1.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>

  <!-- Discover assemblies in /lib -->
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <probing privatePath="lib" />
    </assemblyBinding>
  </runtime>
</configuration>

This took some time to figure out so I am posting it here. Also credits to The PrettyBin NuGet Package. It is a package that moves the dlls automatically. I liked a more manual approach so I did not use it.

Also - here is a post build script that copies all .dll/.xml/.pdb to /Lib. This unclutters the /debug (or /release) folder, what I think people try to achieve.

:: Moves files to a subdirectory, to unclutter the application folder
:: Note that the new subdirectory should be probed so the dlls can be found.
SET path=$(TargetDir)\lib
if not exist "%path%" mkdir "%path%"
del /S /Q "%path%"
move /Y $(TargetDir)*.dll "%path%"
move /Y $(TargetDir)*.xml "%path%"
move /Y $(TargetDir)*.pdb "%path%"
user_41228890
Related