Self-Registering classes in C#

viperashu

I have to make a program that implements a Shape Factory (that is a container that keep all kind of geometric shapes). The trick is, it has to be developped in such a way, to allow adding of new shapes (classes derived from a base abstract class "Shape") without modifing any of the main program's code... I've done it in C++... and it is something like that: //in main program: class Shape { virtual void Draw() = 0; //abstract } //in new file (added afterwards... ) class Circle : Shape { void Draw() {...} } namespace { //by initializing this const, i actually call the function RegisterCircle(...), that // registeres this class (addes some information in a vector) const bool registered = RegisterCircle(...); } because of namespaces in C++, this is OK... But in C#, I can not have variables inside a namespace (not included in a class). So I could use that variable, as a STATIC one, inside my "Circle" class. This would be ok, but for one thing: in C#, no variable (even a static one) gets initialized until its owner class is instantiated or a static member is called (used) in a program... And I can not instantiate or call a static member from the main program, because I'm not allowed to modify main program. So, please help!!!

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bilnaad22y ago
True, C# application are constructed from ONLY classes. Everything must be a class. But not all need to be instanciated. When using static methods that method is not dependant on the object instantiation. So you can use a sealed class (wich cannot be instantiated or inherited) and add some static methods to it. Something like: [code] sealed class Register { public static void RegisterClass(...) { ... ... } } class NewlyCreated { static int variable = Register.RegisterClass(...); }[/code]
viperashu22y ago
No, I know this... I know polimorphism in C++, and there is no big difference in C# or Java... I can understand the differences.. Problem is, I need to access a function from a newly created class which adds some information in a container in the main program. (because I can't modify the main program's code) And I could do this like that: class NewlyCreated { static int variable = Register(...); } This way, by initializing the variable, C# actually calles function Register (which is what I wanted) Problem is, in C# no variable inside a class gets initialized unless I actually use that class. So the variable "variable" gets initialized (and the same time the function Register(...) is calles), only after I instantiate that class, or access this variable "variable" from outside)... And I can not instantiate or access the variable because the main program doesn't know this class exists (was newly added)... I don't know if you understand, it's hard to explain... But I think there is no solution... I have to find some other way... (i will probably do something like a plugin... and this way the program will know there is a new class added...) Thanks anyway
jshepler22y ago
If I understand you correctly, you're talking about what .NET calls Polymorphism. That is calling a method of the base class that the derived class actually executes. In other words, your main program knows it has a Shape and calls the Shape's Draw() method, but you want the derived Circle class to do the actual execution. If this is not what you're asking, ignore the rest of this post and hope someone else understands what you're asking. The base Shape class would still use the virtual keyword in front of the methods that derived classes are to OVERRIDE. public class Shape { ... public virtual void Draw() { // code here that executes when the object actually is a Shape, the derived class // doesn't override this method, or the derived class explicitly calls this method // via base.Draw(); } } public class Circle : Shape { ... public override void Draw() { // code here that executes instead of the base method // if you need to call the base method as well, use base.Draw(); } } As for variables, if you mark the base class' variables as protected, the dervied class can access them - static or otherwise. Your main program works with the Shape "aspect" of the Circle object. When you call the base's Draw() method, the Circle's Draw() method will be executed instead.