Find out if type is instantiable

Question

In C#, how can I find out if a Type can be instantiated? I am trying to avoid an Activator.CreateInstance exception.

My current method is type.IsClass && !type.IsInterface, but I am worried this could fail on abstract classes, etc. I also considered checking type.TypeInitializer == null, but I am not sure if that is foolproof either.

What is the simplest/most efficient way possible to find out if a Type is instantiable?

For it to be "safe" wouldn't he also have to check IsPublic and similar properties on the ConstructorInfo object returned by GetConstructor(). I don't know. I'm asking.. — Simen S, Apr 06 '11 at 19:27

score 13 · Answer 1 · answered Apr 06 '11 at 19:20

13

Consider IsAbstract . It would handle abstract as well as static class. You may also want to check on IsInterface

answered Apr 06 '11 at 19:20

WorldIsRound

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It seems that IsAbstract is returning true for interface as well: https://msdn.microsoft.com/en-us/library/system.type.isabstract(v=vs.110).aspx – Sauleil Mar 28 '18 at 14:20
Don't forget IsGenericTypeDefinition too! Can't create an instance of a generic type with unbound parameters. – IS4 Jan 11 '23 at 18:01

score 9 · Accepted Answer · answered Apr 06 '11 at 19:29

9

There are many other traps. It could have a constructor that is private or protected. Or it might not have a default constructor, only constructors that take certain argument types. If you have to worry about that then you are surely using Activator.CreateInstance() when it should not be used. Just arbitrarily constructing objects can only create havoc, you have no idea what kind of side effects they may have. Avoid the "FormatDisk" class.

An exception is your friend, it tells you that your assumptions were wrong. Never intentionally stop the .NET framework from being helpful.

answered Apr 06 '11 at 19:29

Hans Passant

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I am creating instances of implementations of an interface, so I do know something about them. I appreciate the warning, though. – user664939 Apr 06 '11 at 19:35
Excellent, then you should not have to worry about exceptions or accidentally creating an abstract class. A simple well-known name gets the job done. – Hans Passant Apr 06 '11 at 19:35
How would I go about checking for a default constructor? – user664939 Apr 06 '11 at 19:38
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Also, exceptions are good, but so is gracefully handling them. I would rather check "if (not null)" than "try-catch(null)." – user664939 Apr 06 '11 at 19:48
Accepted for "private constructor" and "non-default constructor" examples. – user664939 Apr 06 '11 at 19:52

Find out if type is instantiable

2 Answers2