CODEWITHSUNDEEP
c#inheritancestatic-constructor
Trevor
Trevor

Reputation: 13457

c# static constructor not called from derived class

class Bus<T>
{
    static Bus()
    {
        foreach(FieldInfo fi in typeof(T).GetFields())
        {
            if(fi.FieldType == typeof(Argument))
            {
                fi.SetValue(typeof(T), new Argument("busyname", "busyvalue"));
            }
        }
    }
}
class Buss : Bus<Buss>
{
    public static Argument field;
}

Any ideas how to make this work so that a reference to the static field in Buss triggers the static constructor in Bus?

Upvotes: 6

Views: 7662

Answers (3)

C.Evenhuis
C.Evenhuis

Reputation: 26446

The static constructor of a generic type is invoked exactly once per Type, when that type is referenced.

Calling Buss x = new Buss() will invoke the static constructor of Bus<Buss>.

Calling Bus<Buss> x = new Bus<Buss>() will also invoke the static constructor of Bus<Buss>, but it will do so for it's type argument Buss, setting Buss.field.

If you create a class Bugs : Bus<Buss> it will never set Bugs.field, as it will first resolve the type argument Buss, which invokes the static constructor of it's base class Bus<Buss>, setting Buss.field. When it tries to call the static constructor of Bugs base class, it will think it had already invoked the static Bus<Buss> constructor and skip it.

Basically if I copy paste your code, create a dummy Argument class and create a new instance of Buss, the static constructor is invoked and Buss.field is set to an instance of Argument, but I do recognize some strange behavoir here in which I'd have to advise not to use reflection from a static method to reach subclasses' statics.

The example you provided only works because Buss is the type argument for itself.

Upvotes: 2

marto
marto

Reputation: 4180

MSDN says that 'Static constructors are not inherited'. I guess this is similar to static fields which are not inherited either.

Upvotes: 1

recursive
recursive

Reputation: 86124

The fact that this matters to you probably means that you are using static constructors wrong.

With that in mind, you could make a static constructor in Buss that manually invokes the static constructor in Bus. Note that it's not possible to run a static constructor more than once.

Upvotes: 3

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