Get class instance dynamically

[tb2500]

Dear all,

I have a problem where I need to re-use the same instance of several classes over and over in my application. Like collections classes.

Is there a way, with reflection for example, of finding out at runtime if an instance of a class already exists and then using that instance?

Or do I have to create Singleton's for each of those classes?

Should I make a class that keeps track of all my other class instances? Is there maybe a pattern to do so?

Thanks in advance for any help.

[tlhintoq]

If you only need ONE instance of a class, like a collection, you could make it STATIC and just use it with a variable that has global scope.

finding out at runtime if an instance of a class already exists

If it does exist didn't you have to assign it *to* something? Wouldn't you just check whatever variable you would have assigned that instance to?

[tb2500]

Ok on the first bit. Yes I could make it static. The problem is that I need this instance in several other different classes then where it was created.

So

Class A
{
     /// Some methods
}
 
Class B
{
A = new A();
a.DoSomething();
}
 
Class C
{
// need same instance of A that B created... 
}

You see what my problem is? An I have like 10 classes where I would need a particular instance of this one class?

@tlhintoq
Yes, but that variable is in another class as above.

[Markus]

Hmm, they'd have to be singletons, no? Also, one class creating a concrete instance of another class breaks encapsulation, doesn't it (unless the object is passed in as an argument)?

[tb2500]

I agree Markus, I think that I would need to implement the Factory pattern or some such to get around my problem. Unless there's another way?

[GaryTexmo]

What I took from what tlhintoq said was make a public class with a public static member that you can access...

public class GlobalContainer
{
  public static A MyA = new A();
}

then...

Class B
{
//A = new A();
//a.DoSomething();
GlobalContainer.MyA.DoSomething();
}
 
Class C
{
// need same instance of A that B created...
GlobalContainer.MyA.<whatever>
}

To be honest, I don't know what a singleton is... wikipedia seems to suggest that it's basically what I just wrote. I don't know what this has to do with "the Factory pattern" though...

Hopefully I've been of some help. Good luck!

[tlhintoq]

Class B
{
A = new A();
a.DoSomething();
}

Shouldn't this be

A a = new A(); // so that a is a new instance of A so you can 
a.DoSomething();
 

[tlhintoq]

What about this? Make lists of your classes at program level so all can see.

Class Program()
{
    List<A> myAs = new List<A>;
    List<B> myBs = new List<B>;
}

Then add to those lists:

Class A
{
     /// Some methods
}
 
Class B
{
   A newA = new A();
   newA.CreatedByProperty = "B";
   program.MyAs.add(newA);
   newA.DoSomething();
}
 
Class C
{
// need same instance of A that B created... 
    program.MyAs[MyAs.Count-1]   {blah blah}
// The most recently added 'A' is the last one in the list
}

Now you have a List<> for each class that any other class can access.
You can add and search properties that let you know what type of class created it.
If you need to know any 'A' already just check the List<> MyA's.
If there is more than zero in the count, then an A exists.
If you need to know who made the existing 'A', check the CreatedBy property of each 'A' in the list