Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people, just like you, are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
Solved

Generic Type Parameters

Posted on 2009-05-15
5
218 Views
Last Modified: 2012-05-07
As an example, if I inspect an object the following type:

public class LookupList<K, T> : IList<T>, IDictionary<K, T>

How would I look up the type corresponding to the generic argument for IList<>? In this case just retrieving GetGenericArguments will return an array of the two types K and T, and it's unclear which is the argument to IList. So what I'd really like to be able to do is test the object to see if it implements IList<> ( i.e. typeof(IList<>).IsInstanceOfType(myObject) ), and then if so retrieve just the IList<> type so I can then retrieve the generic type.

Is that clear? What's the right call?

Thanks in advance!

0
Comment
Question by:ebyrne
  • 4
5 Comments
 
LVL 9

Expert Comment

by:tculler
ID: 24396073
It's really not a good idea to implement both of these interfaces, as they will surely conflict with each other (even though it is possible...). Why implement both, anyway? Due to polymorphism, I'm not sure how to do this--or why it would even be useful.
0
 
LVL 2

Author Comment

by:ebyrne
ID: 24396104
And I suppose I could call GetInterfaces() in this case and iterate through them testing each for it's GenericTypeDefinition, but it seems to me there should be a more direct way (and/or a way that would work with all base classes/interfaces). Is there?
0
 
LVL 2

Author Comment

by:ebyrne
ID: 24396142
tculler,

Thanks for responding, but that's not really an answer or even an attempt. :) To respond though, it seems perfectly reasonable to me. In this case the class is a list that provides the lookup functionality of a dictionary and the normal iteration functionality of a list (and it was just an example I cooked up, not an actual class)...

Thanks for stopping in though!
0
 
LVL 2

Author Comment

by:ebyrne
ID: 24396251
And he does bring up a good point, perhaps it's not an ideal example, but really all I'm getting at is that the class implements several generic interfaces with varying generic parameters. I know what interface I'm interested in, I just want to know how to get the parameter for that interface/class...
0
 
LVL 2

Accepted Solution

by:
ebyrne earned 0 total points
ID: 24396310
Okay, so this is the best I've got so far, supporting only interfaces and a single argument. If you can either provide the more direct route I'm looking for or generalize this to classes and multiple arguments the points are yours.

Thanks Experts!
        static public Type GetGenericArgument(Type type, Type genericTypeDefinition)
        {
            if (type == null || genericTypeDefinition == null)
            {
                throw new ArgumentNullException();
            }
            if (!genericTypeDefinition.IsGenericTypeDefinition)
            {
                throw new ArgumentException("The generic type must be a generic type definition");
            }
            if (!genericTypeDefinition.IsInterface || genericTypeDefinition.GetGenericArguments().Length != 1)
            {
                throw new NotImplementedException("Must be a single argument interface type currently!");
            }
 
            var baseTypes = type.GetInterfaces();
 
            foreach (Type t in baseTypes)
            {
                if (t.IsGenericType && t.GetGenericTypeDefinition() == genericTypeDefinition)
                {
                    var args = t.GetGenericArguments();
 
                    if (args.Length > 0)
                    {
                        return args[0];
                    }
                }
            }
 
            return null;
        }
 
Usage:
        type = GetGenericArgument(dataSource.GetType(), typeof(IEnumerable<>));

Open in new window

0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

We all know that functional code is the leg that any good program stands on when it comes right down to it, however, if your program lacks a good user interface your product may not have the appeal needed to keep your customers happy. This issue can…
A long time ago (May 2011), I have written an article showing you how to create a DLL using Visual Studio 2005 to be hosted in SQL Server 2005. That was valid at that time and it is still valid if you are still using these versions. You can still re…
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online. The email signature template has been downloaded from: www.mail-signatures…
I've attached the XLSM Excel spreadsheet I used in the video and also text files containing the macros used below. https://filedb.experts-exchange.com/incoming/2017/03_w12/1151775/Permutations.txt https://filedb.experts-exchange.com/incoming/201…

808 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question