Create code at runtime with Reflection in .NET C#: Methods

The previous post in this miniseries got us as far as defining a default and an overloaded constructor for our custom type:

ConstructorBuilder defaultConstructorBuilder = simpleType.DefineDefaultConstructor(MethodAttributes.Public);
ConstructorBuilder constructorBuilder = simpleType.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, new Type[] { typeof(string) });

We can add methods to the type in the following ways. Here’s how to create a void method called Calculate which accepts two integers as parameters:

MethodBuilder calculateFunctionBuilder = simpleType.DefineMethod("Calculate", MethodAttributes.Public, null, new Type[] { typeof(int), typeof(int) });

Note the ‘null’ parameter which defines that there’s no return type. Consequently here’s how to add a return type of int:

MethodBuilder calculateFunctionBuilder = simpleType.DefineMethod("Calculate", MethodAttributes.Public, typeof(int), new Type[] { typeof(int), typeof(int) });

If there are no parameters to the method then leave the last item as null:

MethodBuilder calculateFunctionBuilder = simpleType.DefineMethod("Calculate", MethodAttributes.Public, typeof(int), null);

…and here’s how to define a static method:

MethodBuilder calculateFunctionBuilder = simpleType.DefineMethod("Calculate", MethodAttributes.Public | MethodAttributes.Static, typeof(int), null);

We’ll of course need a method body as well and just like we saw in the case of constructors this operation can be quite complex. Check the post on creating constructors programmatically for my notes and links regarding the .NET intermediate language instructions, the ILGenerator and OpCodes objects for further information.

View all posts on Reflection here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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