Fix IsDotNetCore

src/OpenCvSharp/Internal/PInvoke/WindowsLibraryLoader.cs

@@ -84,7 +84,7 @@ public bool IsLibraryLoaded(string dllName)
         }
 
         /// <summary>
-        /// 
+        /// Determine if the OS is Windows
         /// </summary>
         /// <returns></returns>
         public static bool IsCurrentPlatformSupported()
@@ -98,7 +98,7 @@ public static bool IsCurrentPlatformSupported()
         }
 
         /// <summary>
-        /// 
+        /// Determine if the runtime is .NET Core
         /// </summary>
         /// <returns></returns>
         public static bool IsDotNetCore()
@@ -107,7 +107,8 @@ public static bool IsDotNetCore()
             return false;
 #else
             // https://github.com/dotnet/corefx/blob/v2.1-preview1/src/CoreFx.Private.TestUtilities/src/System/PlatformDetection.cs
-            return RuntimeInformation.FrameworkDescription.StartsWith(".NET Core", StringComparison.Ordinal);
+            return Environment.Version.Major >= 5 || 
+                RuntimeInformation.FrameworkDescription.StartsWith(".NET Core", StringComparison.OrdinalIgnoreCase);
 #endif
         }
 

test/OpenCvSharp.Tests/system/WindowsLibraryLoaderTest.cs

@@ -0,0 +1,22 @@
+#nullable enable
+
+using OpenCvSharp.Internal;
+using Xunit;
+
+namespace OpenCvSharp.Tests
+{
+    public class WindowsLibraryLoaderTest
+    {
+        [Fact]
+        public void IsDotNetCore()
+        {
+#if NET48
+            Assert.False(WindowsLibraryLoader.IsDotNetCore());
+#elif NETCOREAPP3_1_OR_GREATER
+            Assert.True(WindowsLibraryLoader.IsDotNetCore());
+#else
+            throw new OpenCvSharpException("Unexpected environment.");
+#endif
+        }
+    }
+}