Prevent calling Public constructors except for XML Serializer

Question

Does anyone know if it is possible to prevent calling of a public constructor from outside a range of assemblies?

What I'm doing is coming up with a class library that has XML serializable classes. These classes make no sense if constructed without setting various properties so I want to prevent that state.

I'm wondering if there is a way to prevent anyone calling my public constructor, and keep it there only for serialization?

Answer 1

Is it required that the constructors be public, or could you make them internal?

Answer 2

If you do not explicitly call any constructor in the base class, the parameterless constructor will be called implicitly. There's no way around it, you cannot instantiate a class without a constructor being called.

Answer 3

To achieve what you are asking, you should probably make the constructor private, and then use a getInstance method to return the object if the correct assembly calls getInstance. You can do a check inside the getInstance method if you pass the object or assembly that called the function as one of its parameters.

Answer 4

You can create a factory method that takes assembly information in parameters and based on it you can filter it

Edit Sorry but i was making the edit and afterwards saw albertoPL answering the same

Answer 5

Typically, I would create a public constructor with parameters that will make the object valid and create a public parameterless constructor with valid default values.

public foo() {
  this.bar = -1;
}

public foo(int bar) {
  this.bar = bar;
}

Private/internal constructor can be used depending on your situation, and you can create a Factory pattern that deals with object creation for external code.

Answer 6

Check this answer: http://stackoverflow.com/questions/267724/why-xml-serializable-class-need-a-parameterless-constructor.

You may create internal or private constructor and still use XML serialization.

Answer 7

I don't know if it would work in your case, but you could check the calling assembly:

if (Assembly.GetCallingAssembly().GetName().Name == "Forbidden.Assembly")
{
    throw new Exception(...);
}

Answer 8

If your actual aim is to make it impossible to instantiate an object of your class except by calling certain constructors, unfortunately that's impossible to ensure.