DllNotFoundException in unity3d plugin for c++ dll

Question

I am working on the Unity Plugin project and try to import the c++ native dll from c# file. But I keep getting dllnotfoundexception.

c++ dll code:

Answer 1

Thanks to this Unity forum post I came up with a nice solution which modifies the PATH-environment variable at runtime:

• Put all DLLs (both the DLLs which Unity interfaces with and their dependent DLLs) in Project\Assets\Wherever\Works\Best\Plugins.

• Put the following static constructor into a class which uses the plugin:

  static MyClassWhichUsesPlugin() // static Constructor
  {
      var currentPath = Environment.GetEnvironmentVariable("PATH",
          EnvironmentVariableTarget.Process);
  #if UNITY_EDITOR_32
      var dllPath = Application.dataPath
          + Path.DirectorySeparatorChar + "SomePath"
          + Path.DirectorySeparatorChar + "Plugins"
          + Path.DirectorySeparatorChar + "x86";
  #elif UNITY_EDITOR_64
      var dllPath = Application.dataPath
          + Path.DirectorySeparatorChar + "SomePath"
          + Path.DirectorySeparatorChar + "Plugins"
          + Path.DirectorySeparatorChar + "x86_64";
  #else // Player
      var dllPath = Application.dataPath
          + Path.DirectorySeparatorChar + "Plugins";
  
  #endif
      if (currentPath != null && currentPath.Contains(dllPath) == false)
          Environment.SetEnvironmentVariable("PATH", currentPath + Path.PathSeparator
              + dllPath, EnvironmentVariableTarget.Process);
  }
  

• Add [InitializeOnLoad] to the class to make sure that the constructor is run at editor launch:

   [InitializeOnLoad]
   public class MyClassWhichUsesPlugin
   {
       ...
       static MyClassWhichUsesPlugin() // static Constructor
       {
           ...
       }
    }
  

With this script there is no need to copy around DLLs. The Unity editor finds them in the Assets/.../Plugins/...-folder and the executable finds them in ..._Data/Plugins-directory (where they get automatically copied when building).