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Unable to cast an object created by Activator.CreateInstance.

Posted on 2004-09-07
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Last Modified: 2012-06-27
Hi there,

I'm having trouble creating objects using the Activator object.

I'm calling it this way:

public object DynamicRetrieval(string classname, string asmPath){
    Assembly asm = Assembly.LoadFrom(asmPath);
    Type dynType = asm.GetType(classname, true, false);
    return = ActivatorCreateInstance(dynType);
}

In another method (& dll) I call:

MyObj myObj = server.DynamicRetrieval("MyObj", "MyObj.dll") as MyObj;

But this always throws an 'InvalidCastException'.
If I place a break point on the line and see what the type of the object returned is, it tells me it is a 'MyObj' object.

I can't see how, if it knows it is a 'MyObj' it can't be cast to it?

The 'DynamicRetreival' method is in a 'Server.dll' that is referenced by 'MyObj.dll'. MyObj.dll contains two classes:
MyObj and Runner.
If you create a new instance of 'Runner' it will attempt to retrieve a new instance of a 'MyObj' class from the Server.

Um, hope you can help!

Thanks

Wint.
0
Comment
Question by:WinterMuteUK
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11 Comments
 
LVL 37

Accepted Solution

by:
gregoryyoung earned 500 total points
ID: 11997769
make sure they are referencing the same version of the assembly ...
0
 
LVL 9

Author Comment

by:WinterMuteUK
ID: 11997816
Yup, the path given is the same path as the build...
0
 
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Expert Comment

by:eternal_21
ID: 11997817
Can you post your *actual* DynamicRetrieval method?
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LVL 9

Author Comment

by:WinterMuteUK
ID: 11997899
Yup, here it is!

public object DynamicRetreival(XmlNode node)
{
      /* Retrieve the data needed... */
      string rNamespace      = node.Attributes.GetNamedItem("namespace").Value;
      string rClassname      = node.Attributes.GetNamedItem("classname").Value;
      string rPath      = node.Attributes.GetNamedItem("path").Value;
                  
      if(rNamespace.Length > 0)
            rClassname = rNamespace + "." + rClassname;

      Assembly asm = Assembly.LoadFrom(rPath);
                  
      Type dynType = asm.GetType(rClassname, true, false);
      object dynObj = Activator.CreateInstance(dynType);
      return dynObj;
}

The xml is:

<Invoke namespace='Wint' classname='MyObj' path='MyObj01.dll' />

0
 
LVL 9

Author Comment

by:WinterMuteUK
ID: 11998068
Ahem,

I've been messing with the location of the MyObj.dll, and now it seems to work:

Originally I had the path of the dll pointing to the build location of the 'MyObj' project (so c:\x\MyObj\bin\debug\MyObj.dll).
I changed the path to the location of the running code (c:\x\Runner\bin\debug\MyObj.dll) and it works, I checked both versions of the files and they are exactly the same (apparently)...

Seeing as this sort of answered the question, and I can only assume it must be some sort of versioning problem, then the questions now are:
Is there any reason for this? Are the files actually different even though the version nums are the same?
0
 
LVL 37

Expert Comment

by:gregoryyoung
ID: 12000744
yeah an object out of 1 dll 1.1.2.1001 is not the same as an oject from a dll 1.1.2.1002
0
 
LVL 37

Expert Comment

by:gregoryyoung
ID: 12000749
now when you say the same are they the same including build number ?
0
 
LVL 9

Author Comment

by:WinterMuteUK
ID: 12004012
Yes both files were: 1.7.3.1338, which is why I couldn't see why it wasn't working....
0
 
LVL 3

Expert Comment

by:PocketMatt
ID: 12004373
uhm... doesn't Activator.CreateInstance return an ObjectHandle?
if so, you'll have to unwrap it first and cast the unwrapped Object.

cheers
0
 
LVL 9

Author Comment

by:WinterMuteUK
ID: 12004572
Depends on which version of CreateInstance you use.
If as i'm doing you pass a 'Type' it will return an object...

Wint....
0
 
LVL 9

Author Comment

by:WinterMuteUK
ID: 12006463
Gregory's answer was correct, but I still don't know why or how the files differed with exactly the same version nums. At least it works, and that's what counts!

Thanks guys

Wint.
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