Modifying class at runtime

[Lord Zoltar]

Is it possible with the classes in Reflection.Emit to modify a method
of an existing class?
I would like to print some diagnostic messages every time certain
methods are called. I don't want to start adding code to every part of
my program that calls these methods, and the code came as a DLL so I
can't modify the source.

Here's something close to what I've tried:

Assembly currentAssembly = Assembly.GetExe cutingAssembly( );
Type[] types = currentAssembly .GetTypes();
....//other unrelated code removed...
AppDomain appDomain = AppDomain.Curre ntDomain;
AssemblyBuilder assbuild =
appDomain.Defin eDynamicAssembl y(currentAssemb ly.GetName(),
AssemblyBuilder Access.Run);
//types[j] is the index in types of the type I need to modify.
ModuleBuilder myModuleBuilder =
assbuild.Define DynamicModule(t ypes[j].Module.Name);

TypeBuilder myTypeBuilder = myModuleBuilder .DefineType(t.N ame,
TypeAttributes. Public);

MethodBuilder myMethod = myTypeBuilder.D efineMethod(mi. Name,
MethodAttribute s.Public, CallingConventi ons.Standard, null,
myMethodArgs);

ILGenerator methodIL = myMethod.GetILG enerator();
methodIL.EmitWr iteLine("Trace method: " + mi.Name);
methodIL.Emit(O pCodes.Nop,
mi.GetMethodBod y().GetILAsByte Array().ToStrin g());
types[j] = myTypeBuilder.C reateType();

I had hoped that the line
types[j]=myTypeBuilder. CreateType();
but when I try to use objects of this type, the logging statement does
not appear. Is what I'm trying to do even possible?

[Jon Skeet [C# MVP]]

Re: Modifying class at runtime

Lord Zoltar <lord.zoltar@gm ail.comwrote:

Is it possible with the classes in Reflection.Emit to modify a method
of an existing class?
I would like to print some diagnostic messages every time certain
methods are called. I don't want to start adding code to every part of
my program that calls these methods, and the code came as a DLL so I
can't modify the source.

If you can't modify the source, you may *legally* not be allowed to do
anything. However, PostSharp (http://www.postsharp.org) may be able to
help you.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com

[Lord Zoltar]

Re: Modifying class at runtime

On Oct 1, 1:29 am, Jon Skeet [C# MVP] <sk...@pobox.co mwrote:

Lord Zoltar <lord.zol...@gm ail.comwrote:

Is it possible with the classes in Reflection.Emit to modify a method
of an existing class?
I would like to print some diagnostic messages every time certain
methods are called. I don't want to start adding code to every part of
my program that calls these methods, and the code came as a DLL so I
can't modify the source.

>
If you can't modify the source, you may *legally* not be allowed to do
anything. However, PostSharp (http://www.postsharp.org) may be able to
help you.
>

Heh it's not so much a legal matter as I compiled an old project to
DLL and didn't really want to add debug statements all over it and
rebuild it... I thought it would be much cleaner to just add the debug
logging in the new project, and I was also kinda curious to play with
the Emit namespace...
That PostSharp system looks very interesting, I'll definitely have to
give it a look. Thanks!