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Class in DLL crashes application

I am using Microsoft Visual Studio Professional 2022 (64-bit), I am trying to add classes to a DLL. Previously I have created a DLL which contains string resources and this works fine. However any attempt at adding a class, even the simplest example, crashes. Here is my demo DLL class:

namespace SimonP {
    public class clsTest {
        public static void ShowName() {
            Console.WriteLine("Hello World");
        }
    }
}

This is the project (.sln) file:

Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio Version 17
VisualStudioVersion = 17.8.34525.116
MinimumVisualStudioVersion = 10.0.40219.1
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SimonP", "SimonP.csproj", "{A483645B-2014-47B0-BD80-DA56F4356D3F}"
EndProject
Global
    GlobalSection(SolutionConfigurationPlatforms) = preSolution
        Debug|Any CPU = Debug|Any CPU
        Release|Any CPU = Release|Any CPU
    EndGlobalSection
    GlobalSection(ProjectConfigurationPlatforms) = postSolution
        {A483645B-2014-47B0-BD80-DA56F4356D3F}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
        {A483645B-2014-47B0-BD80-DA56F4356D3F}.Debug|Any CPU.Build.0 = Debug|Any CPU
        {A483645B-2014-47B0-BD80-DA56F4356D3F}.Release|Any CPU.ActiveCfg = Release|Any CPU
        {A483645B-2014-47B0-BD80-DA56F4356D3F}.Release|Any CPU.Build.0 = Release|Any CPU
    EndGlobalSection
    GlobalSection(SolutionProperties) = preSolution
        HideSolutionNode = FALSE
    EndGlobalSection
    GlobalSection(ExtensibilityGlobals) = postSolution
        SolutionGuid = {C307CDC2-0CE5-46C5-9B0F-5BD811779D98}
    EndGlobalSection
EndGlobal

In my C# application, at the top of FrmMain.cs:

using SimonP;

Later in the FrmMain constructor:

public FrmMain() {
    try {
        SimonP.clsTest.ShowName();
    } catch(FileNotFoundException ex) {
        Console.WriteLine("HACK");
    }
}

I've built this and am running it only in the debugger, but as soon as I start debugging I get:

System.IO.FileNotFoundException
  HResult=0x80070002
  Message=Could not load file or assembly 'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
  Source=Project
  StackTrace:
   at Project.FrmMain..ctor() in C:\LocalDev\VisualStudio\Project\FrmMain.cs:line 55
   at Project.Program.Main() in C:\LocalDev\VisualStudio\Project\Program.cs:line 24

I've searched online for demos and examples and I really can't see what I've done wrong.

When running in debug I've tried to add a Watch to 'SimonP.clsTest.ShowName' the Value shows:

error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

I just create a simple Console project, added the reference to the DLL and the exact same call, it worked with no exceptions.

I then create another project this time a Windows Forms App (.NET Framework), added the reference to the dll and the same call to Form1.cs Form1() after InitializeComponet() and I get:

System.IO.FileNotFoundException
  HResult=0x80070002
  Message=Could not load file or assembly 'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
  Source=SimonPApp
  StackTrace:
   at SimonPApp.Form1..ctor() in C:\LocalDev\VisualStudio\SimonP\SimonPApp\Form1.cs:line 17
   at SimonPApp.Program.Main() in C:\LocalDev\VisualStudio\SimonP\SimonPApp\Program.cs:line 16

SimonPApp project properties, Application, Target framework:.NET Framework 4.7.2

Build Platform:Active (Any CPU)

Platform target:x64

Prefer 32-bit:unchecked

Solution

  • Your exception message reveals a hint to solving the problem:

    System.IO.FileNotFoundException
 HResult=0x80070002
 Message=Could not load file or assembly 'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
    • System.Runtime, Version=8.0.0.0 refers to a BCL assembly from .NET 8.0, which the CLR is saying it can't find...
      • ...this specific error mostly (only?) happens when the entrypoint program (i.e. the .exe with the Program.Main() method) is running in an older version of .NET and tries to load and run a .dll file targeting a newer version of .NET.
    • Your .sln file has this line: Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SimonP", "SimonP.csproj"
      • ...which tells us that your SimonP.csproj project file targets .NET Framework 4.x (because FAE04EC0... is the well-known-GUID for .csproj files predating the newer "SDK-style" .csproj) and these project-files cannot reference .NET 8.
      • ...which tells us that SimonP.csproj is likely targeting .NET Framework 4.x and trying to load a .dll which targets .NET 8.0, and that's going to fail.
    • Therefore, either:
      • Migrate SimonP.csproj to an SDK-style project file and change the <TargetFramework> to net8.0.
      • ...or update the .csproj for your hitherto unnamed .dll file to target .NET Framework 4.x or .NET Standard 2.0 instead of .NET 8.0.