How do I invoke a static constructor with reflection?

Question

How can I get the ConstructorInfo for a static constructor?

public class MyClass 
{
    public static int SomeValue;

    static MyClass() 
    {
        SomeValue = 23;
    }
}

I've tried the following and failed....

Type myClass = typeof (MyClass);

// throws exception
myClass.TypeInitializer.Invoke(null);

// returns null (also tried deleting  BindingFlags.Public
ConstructorInfo ci = myClass.GetConstructor(
    BindingFlags.Static | BindingFlags.Public,\
    System.Type.DefaultBinder,
    System.Type.EmptyTypes,
    null);

// returns empty array
ConstructorInfo[] clutchingAtStraws = myClass.GetConstructors
   (BindingFlags.Static | BindingFlags.Public);

Oliver · Answer 1 · 2015-08-24T11:21:17.790

37

There is also System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(RuntimeTypeHandle type), which additionally guarantees that the static constructor is only called once, regardless how many times the method is called:

Type myClass = typeof(MyClass);
System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(myClass.TypeHandle);

Reference

edited Aug 24 '15 at 11:21

answered Feb 26 '15 at 09:06

Oliver

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score 34 · Accepted Answer · edited May 23 '17 at 11:54

34

Use myClass.TypeInitializer.Invoke(null, null).

I've just tried this and it worked fine.

I would strongly recommend that you don't do this, however - it violates a type expecting the static constructor to only be executed once. Use RuntimeHelpers.RunClassConstructor as per Oliver's answer if you're just trying to ensure a class is initialized.

edited May 23 '17 at 11:54

Community

1
1

answered Mar 26 '10 at 16:33

Jon Skeet

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9,194

I needed to access it in order [to apply an aspect to it using PostSharp](http://www.sharpcrafters.com/). I guess that still is a valid use case. – Steven Jeuris Mar 24 '12 at 01:00
2

Downvoted, just because next answer is (at least in theory) much safer. p.s. ...Damn it, I just downvoted Jon Skeet's answer. Am not I bold? – Andriy K Nov 26 '16 at 01:02
2

@AndriyK: Have added a link to `RunClassConstructor`, and given credit to Oliver's answer. – Jon Skeet Nov 26 '16 at 08:12

score 7 · Answer 3 · answered Mar 26 '10 at 16:37

Even though it is possible, it may not be a good idea to do that. However, if you access any member of the class, the runtime will invoke the static constructor automatically for you. For example:

// Read the field 'SomeValue', so that the runtime invokes static ctor   
Type myClass = typeof(MyClass);
myClass.GetField("SomeValue").GetValue(null);

Since accessing a field of the class cannot cause any side-effect (other than initialization of the class and call to the static constructor), this should be a relatively safe way to do this in general (however, it will stil work only for classes with some static field). This has the benefit that it guarantees that the type constructor will be invoked at most once which is quite important.

Weird, but I came to this question just because readonly field I needed wasn't initiated at the time when I was accessing it. I can bet, that most people are here for very same reason. — Andriy K, Nov 26 '16 at 00:53

score 2 · Answer 4 · answered Mar 26 '10 at 16:33

Did you also try BindingFlags.Private?

Note, that the static constructor is guaranteed the get called before any call the any other instance or static methods of this class, and it is guaranteed the be threadsafe and called exactly once.

If you would explicitly call it with reflection you could do lots of harm..

How do I invoke a static constructor with reflection?

4 Answers4

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