Reflection has many purposes, but what happens if one wants to instantiate a generic class? How does one specify the what makes the class generic to instantiate it? The trick is to use the MakeGenericType to make the argument(s) and then call create Instance. Here is a code snippet:
Type d1 = typeof(List<>);
Type[] typeArgs = { typeof(string) };
Type makeme = d1.MakeGenericType(typeArgs);
object o = Activator.CreateInstance(makeme);
List<string> itsMe = o as List<string>;
Console.WriteLine((itsMe == null) ? "Failed" : "Succeeded");
Here is what is going on
- Line 1 We get the type as normal.
- Line 3 Create an array of the arguments we are interested in.
- Line 5 Call MakeGenericType to do the magic
- Line 7 Create the object.
#1 by Bishoy on November 17, 2008 - 1:31 am
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How can we create the instance with Reflection.Emit ??
#2 by Max on November 20, 2008 - 6:08 am
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Hi,
thanks for this snippet. Very cool
Cheers
Max
#3 by Julien on January 20, 2009 - 7:52 am
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Thanks for the snippet, it saved me some time
#4 by Johann on January 28, 2009 - 6:02 am
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//A shortened version of the same code
List genericList = (List)Activator.CreateInstance(typeof(List).MakeGenericType(typeof(string)));
#5 by Hossam on May 31, 2009 - 2:36 am
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very helpful solution, thanks allot.
#6 by Matthew Brand on May 29, 2010 - 10:58 am
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Hi,
On line 9, you have to know at compile time that you want a List.
What can you do if you only know you want string at runtime?
How can you tell the C# .NET that “o” is a List where x is not known until runtime? Is there a way to access the methods of List from “o”?
#7 by Matthew Brand on May 29, 2010 - 11:00 am
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By the way, the formatting got a bit messed up in my post. Looks like using angled brackets causes a problem.
Should be:
Hi,
On line 9, you have to know at compile time that you want a List OpenAngleBracket string CloseAngleBracket.
What can you do if you only know you want string at runtime?
How can you tell the C# .NET that “o” is a List OpenAngleBracket x CloseAngleBracket where x is not known until runtime? Is there a way to access the methods of List OpenAngleBracket CloseAngleBracket from “o”?
#8 by Shah on July 17, 2010 - 4:43 am
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Thanks for the above code snippet. It is really helpful.
#9 by yanggu on December 23, 2010 - 6:48 pm
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Hi, thanks for your code first.
I encounter one similar situation recently. i need to read some configuration to load and create objects dynamically.
IPlugin is generic in my code, which is public interface IPlugin.
And concrete plugin implements IPlugin in another different assembly, which is public class ConcretePlugin : IPlugin.
in my config file, i specify the assembly name and also class name of ConcretePlugin.
In my main app, I use the following code to create instance:
Type ct = Assembly.Load(assemblyName).GetType(className);
Activator.CreateInstance(ct.MakeGenericType(typeof(int));
As it is a generic type, i have to config the class name as “ConcretePlugin`1″ rather than “ConcretePlugin”, i don’t think it is very beautiful to write configuration like this.
Do u know any ways to improve this? thx.
#10 by OmegaMan on December 24, 2010 - 1:39 pm
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No it sounds good. You might want to decorate your classes with custom attributes for extra info when/if needed.
#11 by Guy on May 14, 2011 - 11:32 pm
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On line 9, you have to know at compile time that you want a List OpenAngleBracket string CloseAngleBracket.
What can you do if you only know you want string at runtime?
How can you tell the C# .NET that “o” is a List OpenAngleBracket x CloseAngleBracket where x is not known until runtime? Is there a way to access the methods of List OpenAngleBracket CloseAngleBracket from “o”?
#12 by OmegaMan on May 15, 2011 - 8:54 am
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Once one knows the type, such as using typeof( -object goes here-), one can call the method GetGenericArguments() on its result to get its generic arguments.
Such as this Generic method to do the same as above
public static TPrimary Instantiate<TPrimary>() { Type primary = typeof(TPrimary); var ofType = primary.GetGenericArguments(); var typeDef = primary.GetGenericTypeDefinition(); return (TPrimary)Activator.CreateInstance(primary); }HTH
#13 by Vipin Chaudhary on November 15, 2011 - 9:13 am
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Really this is a good article, which helps a lot for beginners as me as well as developer.
This link….
http://www.mindstick.com/Blog/165/Generic%20class%20in%20c
also helpful to understand about generic class in C#
Thanks.
#14 by Artak Mkrtchyan on July 11, 2012 - 5:24 pm
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Thanks for good tip. I’ve actually covered the same topic in my blog. So maybe it may be of interest: http://mkartak.blogspot.ie/2012/03/reflection-working-with-generic-types.html