Failed to load OpenCvSharpExtern.dll using .NET Framework 3.5

[LeonidVasilyev]

I use OpenCvSharp3-AnyCPU 3.2.0.20170419, .NET Framework 3.5, Visual Studio 2015 on Windows 8.1 x64. Exception is thrown every time. Same code works fine using .NET Framework 4.0 and newer.

Steps to reproduce:

1. Create console application with single Program.cs file:

using OpenCvSharp;

namespace Foo
{
    class Program
    {
        static void Main(string[] args)
        {
            var mat = new Mat(100, 100, MatType.CV_8UC1, new Scalar(0));
            Cv2.ImShow("test", mat);
            Cv2.WaitKey();
        }
    }
}

2. Install OpenCvSharp3-AnyCPU 3.2.0.20170419 using NuGet package manager
3. Launch application using Ctrl+F5

Actual result:
Application crashes with unhandled exception:

System.TypeInitializationException: The type initializer for 'OpenCvSharp.Mat' threw an exception. ---> System.DllNotFoundException: Unable to load DLL 'OpenCvSharpExtern': The specified module could not be found. (Exception from HRESULT: 0
x8007007E)
at OpenCvSharp.NativeMethods.core_Mat_sizeof()
at OpenCvSharp.Mat..cctor() in C:\projects\opencvsharp\src\OpenCvSharp\Module
s\core\Mat\Mat.cs:line 610
--- End of inner exception stack trace ---
at OpenCvSharp.Mat..ctor(Int32 rows, Int32 cols, MatType type, Scalar s)
at Foo.Program.Main(String[] args)

Expected result:
Black square image is shown

[thienvu20]

I got the same problem, in the mean time you can add an initialize an cvSVMparam = new cvSVMParam(); and use mat

[shimat]

Please try to call OpenCvSharp.NativeMethods.IsUnix() before your code.

NativeMethods.IsUnix();

var mat = new Mat(100, 100, MatType.CV_8UC1, new Scalar(0));
Cv2.ImShow("test", mat);
Cv2.WaitKey();

This is because static constructor seems not to work in .NET 3.5 or older. 😩

static class Foo
{
    static Foo()
    {
        Console.WriteLine("static constructor");
    }

    [DllImport("kernel32")]
    public static extern int Beep(uint dwFreq, uint dwDuration);
}
class Program
{
    static void Main()
    {
        // "static constructor" not displayed
        Foo.Beep(1000, 1000);
    }
}

[LeonidVasilyev]

The OpenCvSharp.NativeMethods.IsUnix(); call allows me to successfully create matrix instance, yet I couldn't reproduce issue with static constructor in Visual Studio 2015 Community.

[shimat]

I found another condition. The problem occurs if P/Invoke class has [SuppressUnmanagedCodeSecurity] attribute and the .NET version is 3.5 or older.

https://github.com/shimat/opencvsharp/blob/master/src/OpenCvSharp/PInvoke/NativeMethods.cs#L20

I will remove SuppressUnmanagedCodeSecurity when .NET < 4.0

#if DOTNET_FRAMEWORK && !net20
[SuppressUnmanagedCodeSecurity]
#endif
static class NativeMethods
{
   ...