System.TypeLoadException – Could not load type ‘xyz’

The System.TypeLoadException with the message “Could not load type ‘xyz'” occurs in C# when the runtime is unable to load a specific type. This typically happens due to issues such as missing assemblies, mismatched versions, or incorrect type names.

Common Causes and Solutions

1. Missing Assembly:
   If the assembly containing the type is not referenced or not available at runtime, this exception will occur.

   // Example: Trying to use a type from a missing assembly
   var type = Type.GetType("MissingNamespace.MissingClass"); // TypeLoadException

Fix: Ensure the required assembly is referenced and available.

   // Add a reference to the missing assembly in your project
   var type = Type.GetType("ExistingNamespace.ExistingClass"); // Works if the assembly is referenced

2. Incorrect Type Name:
   If the type name is misspelled or does not exist, this exception will occur.

   var type = Type.GetType("MyNamespace.MyClasss"); // Typo in type name

Fix: Verify the type name and ensure it is correct.

   var type = Type.GetType("MyNamespace.MyClass"); // Correct type name

3. Mismatched Assembly Versions:
   If the assembly version used at runtime does not match the version expected by the application, this exception can occur. Fix: Ensure the correct version of the assembly is referenced and deployed.

   // Use binding redirects in the app.config or web.config to resolve version conflicts
   <dependentAssembly>
       <assemblyIdentity name="MyAssembly" publicKeyToken="..." culture="neutral" />
       <bindingRedirect oldVersion="1.0.0.0" newVersion="2.0.0.0" />
   </dependentAssembly>

4. Type Moved or Renamed:
   If the type has been moved to a different namespace or assembly, this exception can occur. Fix: Update the code to use the correct namespace and assembly.

   // Old code
   var type = Type.GetType("OldNamespace.MyClass");

   // Updated code
   var type = Type.GetType("NewNamespace.MyClass");

5. Type Visibility:
   If the type is not public or is internal and not accessible from the calling assembly, this exception can occur. Fix: Ensure the type is public or use InternalsVisibleTo to make it accessible.

   // In the assembly containing the internal type
   [assembly: InternalsVisibleTo("CallingAssembly")]

6. Generic Type Issues:
   If you attempt to load a generic type without specifying the type arguments, this exception can occur.

   var type = Type.GetType("MyNamespace.MyGenericClass"); // Missing type arguments

Fix: Provide the type arguments for the generic type.

   var type = Type.GetType("MyNamespace.MyGenericClass`1[[System.Int32]]"); // Correct generic type

7. Assembly Loading Context:
   If the assembly is loaded in a different context (e.g., LoadFrom context instead of Load context), this exception can occur. Fix: Use Assembly.Load instead of Assembly.LoadFrom to ensure the correct context.

   var assembly = Assembly.Load("MyAssembly");
   var type = assembly.GetType("MyNamespace.MyClass"); // Works in the correct context

8. Platform or Framework Mismatch:
   If the type is specific to a platform or framework (e.g., .NET Core vs .NET Framework), this exception can occur. Fix: Ensure the correct platform or framework is targeted.

   // Verify the target framework in the project file
   <TargetFramework>net6.0</TargetFramework>