WeakReference Classe

using System;
using System.Timers;

class Program
{

    static void Main(string[] args)
    {

        // Creating an instance
        // of an object creates
        // a strong reference.
        ClassA objA1 = new ClassA();

        // Create a short weak reference to the object.
        // Specify true for a long weak reference.
        WeakReference wr = new WeakReference(objA1, false);

        // Set the target of the
        // weak reference to the object.
        wr.Target = objA1;

        // Remove the strong reference
        // the application has to the object.
        objA1 = null;
        if (objA1 == null)
        {
            Console.WriteLine("After setting objA1 to null: objA1 is null.");
        }

        // Set a timer to set a strong reference
        // and to force garbage collection.
        System.Timers.Timer aTimer = new System.Timers.Timer();

        // Set interval to 5 seconds.
        aTimer.Interval = 5000;
        aTimer.Enabled = true;

        // Counter for tracking.
        int count = 1;

        // Anonymous method.
        aTimer.Elapsed += delegate(object sender,
            System.Timers.ElapsedEventArgs e)
        {
            if (objA1 == null)
            {
                Console.WriteLine("objA1 is null");

                // Adjust the count higher if
                // you want to allow more time
                // for automatic garbage collection.
                if (count == 5)
                {
                    // Uncomment next line to set a strong reference.
                    //objA1 = (ClassA)wr.Target;
                    GC.Collect();
                }

                if (count == 8)
                {
                    // This code is only reached if
                    // the weak reference is long.
                    objA1 = (ClassA)wr.Target;

                }
                if (wr.IsAlive == false)
                {
                    // Object is collected and
                    // all references terminated.
                    Console.WriteLine("Object collected");
                    aTimer.Stop();
                }
                else
                {
                    Console.WriteLine("count {0}, still alive. long weak reference: {1}",
                        count.ToString(),
                        wr.TrackResurrection.ToString());
                    count++;
                }
            }
            else
            {
                // A strong reference is established
                // and prevents it being collected.
                Console.WriteLine("Strong reference applied");
                aTimer.Stop();
            }
        };
    }

}
public class ClassA
{
    public ClassA()
    {

    }

    ~ClassA()
    {
        Console.WriteLine("Finalized.");
    }

    void MakeSomeGarbage()
    {
        // Create objects and release them
        // to fill up memory with unused objects.
        Version vt;

        for (int i = 0; i < 10000; i++)
        {
            vt = new Version();
        }
    }
}


// -------- Code example output --------
//
// A short weak reference creates
// the following output:
// ------------------------------------
// After setting objA1 to null: objA1 is null.
// objA1 is null
// count 1, still alive. long weak reference: False
// objA1 is null
// count 2, still alive. long weak reference: False
// objA1 is null
// count 3, still alive. long weak reference: False
// objA1 is null
// count 4, still alive. long weak reference: False
// objA1 is null
// Object collected
// Finalized.
// ------------------------------------
//
//
// A long weak reference creates
// the following output, being
// ressurected at count 5.
// ------------------------------------
// After setting objA1 to null: objA1 is null.
// objA1 is null
// count 1, still alive. long weak reference: True
// objA1 is null
// count 2, still alive. long weak reference: True
// objA1 is null
// count 3, still alive. long weak reference: True
// objA1 is null
// count 4, still alive. long weak reference: True
// objA1 is null
// count 5, still alive. long weak reference: True
// Finalized.
// objA1 is null
// count 6, still alive. long weak reference: True
// objA1 is null
// count 7, still alive. long weak reference: True
// objA1 is null
// count 8, still alive. long weak reference: True
// Strong reference applied
// ----------------------------------
//
//
// A weak reference creates
// the following output with a
// strong reference applied
// at count 5.
// ----------------------------------
// After setting objA1 to null: objA1 is null.
// objA1 is null
// count 1, still alive. long weak reference: False
// objA1 is null
// count 2, still alive. long weak reference: False
// objA1 is null
// count 3, still alive. long weak reference: False
// objA1 is null
// count 4, still alive. long weak reference: False
// objA1 is null
// count 5, still alive. long weak reference: False
// Strong reference applied
// ------------------------------------
//