in C# does Static constructor run for each initialization of object, or only once?

Question

in my Class I have a static dictionary of strings object which contains a big number of Items (it reads from a file and initial them) I wrote a static constructor to do so and i

Answer 1

It runs once for the type, per AppDomain. Not once per instance. From the C# 4 spec, section 10.12:

The static constructor for a closed class type executes at most once in a given application domain. The execution of a static constructor is triggered by the first of the following events to occur within an application domain:

• An instance of the class type is created.
• Any of the static members of the class type are referenced.

Note the part about it being per closed class. So if you have a generic type Foo<T>, then Foo<string> is a separate type to Foo<object> (etc), will have separate static fields, and will have its static constructor invoked separately.

Answer 2

It runs one time only during the lifetime of the application.

From MSDN - Static Constructors:

A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed once only. It is called automatically before the first instance is created or any static members are referenced.