c# - Is there a way to build a new type during Runtime?

Question

I am going to ask a question that might sound weird.

Is there a way to build a new class during Runtime? Or at least, add a new property to an existing class.

I mean creating a class that doesn't exist and not an instance of an existing class. I could later on use reflections to load and use this class.

Answer 1

Adding a property to an existing type is not possible, but you can create a new type at runtime using Reflection.Emit. It's pretty complicated stuff, and it goes something like this:

AssemblyBuilder assemblyBuilder = Thread.GetDomain().DefineDynamicAssembly(
      assemblyName , AssemblyBuilderAccess.Run, assemblyAttributes);
ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("ModuleName");
TypeBuilder typeBuilder = moduleBuilder.DefineType(
      "MyNamespace.TypeName" , TypeAttributes.Public);

typeBuilder.DefineDefaultConstructor(MethodAttributes.Public);

// Add a method
newMethod = typeBuilder.DefineMethod("MethodName" , MethodAttributes.Public);

ILGenerator ilGen = newMethod.GetILGenerator();

// Create IL code for the method
ilGen.Emit(...);

// ...

// Create the type itself
Type newType = typeBuilder.CreateType();

This code is just a sample. It could contain errors.

You can also generate classes by compiling C# source code at runtime using System.CodeDom, but I don't know a lot about that.