DynamicMethod NullReferenceException

Question

Can anyone tell me what's wrong with my IL code here?

IL_0000: nop        
IL_0001: ldarg.1    
IL_0002: isinst     MyXmlWriter
IL_0007: stloc.0    
IL_0008: ldloc.0    
IL_0009: ldarg.2    
IL_000a: ldind.ref  
IL_000b: unbox.any  TestEnum
IL_0010: ldfld      Int64 value__/FastSerializer.TestEnum
IL_0015: callvirt   Void WriteValue(Int64)/System.Xml.XmlWriter
IL_001a: nop        
IL_001b: ret

I'm going crazy here, since I've written a test app which does the same thing as above, but in C#, and in reflector the IL code from that looks just like my DynamicMethod's IL code above (except my test C# app uses a TestStruct with a public field instead of the private value field on the enum above, but I have skipVisibility set to true)...

I get a NullReferenceException.

My DynamicMethod's signature is:

public delegate void DynamicWrite(IMyXmlWriter writer, ref object value, MyContract contract);

I generate the method like this:

List<Type> parameterTypes = new List<Type> { 
   typeof(DMBuilder), 
   typeof(IDynamicSerializationWriter), 
   typeof(object).MakeByRefType(), 
   typeof(MyContract) 
}; 
DynamicMethod dm = new DynamicMethod(string.Format(
  "Write_{0}", 
  contract.TypeName), 
  typeof(void), 
  parameterTypes.ToArray(), 
  typeof(DMBuilder), 
  true
);

var d = dm.CreateDelegate(typeof(DynamicWrite), this);
d(x,y);

And I'm definitely not passing in anything null.

Thanks in advance!

Possible duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Nasreddine, Oct 04 '15 at 09:08

score 1 · Answer 1 · answered Mar 12 '10 at 17:53

1

Forced to take a guess, I'd gamble at you emitting a static method but used an instance method in your C# code. There's definitely a "this" argument (arg.0) but it is never used. Declare it static, compile and disassemble again.

answered Mar 12 '10 at 17:53

Hans Passant

922,412
146
1,693
2,536

I am indeed using it as a DynamicMethod on an instance, but I don't think I'm emitting it as static: List parameterTypes = new List { typeof(DMBuilder), typeof(IDynamicSerializationWriter), typeof(object).MakeByRefType(), typeof(MyContract) }; DynamicMethod dm = new DynamicMethod(string.Format("Write_{0}", contract.TypeName), typeof(void), parameterTypes.ToArray(), typeof(DMBuilder), true); Is that incorrect? – Jeff Mar 12 '10 at 18:05
@Jeff: that's a static method. It explains your problem, your code is using the wrong arguments. – Hans Passant Mar 12 '10 at 18:38
Sorry, I guess I'm not fully understanding. I should have included the next line: var d = dm.CreateDelegate(typeof(DynamicWrite), this) Then I invoke like: d(x,y); What should I be doing differently? Thanks. – Jeff Mar 12 '10 at 18:50
What is the type of "this" you are passing to CreateDelegate? You didn't declare it as an argument to the method. Don't forget: instance methods have a hidden extra 1st argument that passes the object reference. – Hans Passant Mar 12 '10 at 19:33
This is a DMBuilder instance, the first argument in my List above that I pass in as type parameters for the DynamicMethod, the delegate signature itself doesn't have this first parameter (since it's hidden). – Jeff Mar 12 '10 at 20:44
@Jeff: I edited your post, couldn't read it properly in the comments. The delegate call is not correct, please fix it. – Hans Passant Mar 12 '10 at 21:09

score 0 · Answer 2 · answered Jan 07 '15 at 21:14

0

IL_0002 isinst

this instruction push a null in local.0. You can remove it.

answered Jan 07 '15 at 21:14

Teter28

504
5
8

DynamicMethod NullReferenceException

2 Answers2