WeakReference. This C# type influences the garbage collector. Most objects that are referenced must be kept in memory until they are unreachable.

But with WeakReference, objects that are referenced can be collected. We can use WeakReference to allow access to objects until they must be removed from memory.

An example. The WeakReference type is created using a constructor call. You must pass the object reference you want to point to the constructor. Here we use a StringBuilder object.

Constructor

StringBuilder

GC.Collect

as

is

using System;
using System.Text;

class Program
{
    /// <summary>
    /// Points to data that can be garbage collected any time.
    /// </summary>
    static WeakReference _weak;

    static void Main()
    {
        // Assign the WeakReference.
        _weak = new WeakReference(new StringBuilder("perls"));

        // See if weak reference is alive.
        if (_weak.IsAlive)
        {
            Console.WriteLine((_weak.Target as StringBuilder).ToString());
        }

        // Invoke GC.Collect.
        // ... If this is commented out, the next condition will evaluate true.
        GC.Collect();

        // Check alive.
        if (_weak.IsAlive)
        {
            Console.WriteLine("IsAlive");
        }

        // Finish.
        Console.WriteLine("[Done]");
        Console.Read();
    }
}
perls
[Done]

A discussion. Is using the WeakReference type a good idea? Unfortunately, the behavior of the garbage collector is not always predictable and can even vary when the runtime is updated.

A review. WeakReference influences the GC. When a collection is done, either forced or invoked by the runtime, objects that are only referenced through WeakReference can be collected.

Therefore, you must check these objects for life upon each access. The IsAlive method is used for this purpose—it makes code more complex.