Any sense to set obj = null(Nothing) in Dispose()?

Question

Is there any sense to set custom object to null(Nothing in VB.NET) in the Dispose() method? Could this prevent memory leaks or it's useless?!

Let's consider two examples:

public class Foo : IDisposable {     private Bar bar; // standard custom .NET object      public Foo(Bar bar) {         this.bar = bar;     }     public void Dispose() {         bar = null; // any sense?     } }  public class Foo : RichTextBox {     // this could be also: GDI+, TCP socket, SQl Connection, other "heavy" object     private Bitmap backImage;       public Foo(Bitmap backImage) {         this.backImage = backImage;     }      protected override void Dispose(bool disposing) {         if (disposing) {             backImage = null;  // any sense?         }     } } 

Answer 1

Personally I tend to; for two reasons:

• it means that if somebody has forgotten to release the Foo (perhaps from an event) any downstream objects (a Bitmap in this case) can still be collected (at some point in the future - whenever the GC feels like it); it is likely that this is just a shallow wrapper around an unmanaged resource, but every little helps.
  • I really don't like accidentally keeping an entire object graph hanging around just because the user forgot to unhook one event; IDisposable is a handy "almost-kill" switch - why not detach everything available?
• more importantly, I can cheekily now use this field to check (in methods etc) for disposal, throwing an ObjectDisposedException if it is null

Answer 2

The purpose of Dispose() is to allow clean up of resources that are not handled by the garbage collector. Objects are taken care of by GC, so there's really no need to set the reference to null under normal circumstances.

The exception is if you expect the caller to call Dispose and hold on to the instance after that. In that case, it can be a good idea to set the internal reference to null. However, disposable instances are typically disposed and released at the same time. In these cases it will not make a big difference.