Disposing objects in C#

Have you ever been confused of object disposing, when object is garbage collected and what does the Using-block do? Below is a code sample that shows what happends to an object when it loses its references and is garbage collected, and what happends to object after using-block.

Basically, when you use the using block, when the code is done the object's Dispose-method gets called. And you need to implement the IDisposable interface for that. When you're not using the using-block and object gets garbage collected, object's destructor/finalizer gets called.

    1 using System;

    2 

    3 namespace DisposeTest

    4 {

    5   class Tester

    6   {

    7     static void Main(string[] args)

    8     {      

    9       // Note: we create objects in separate method, because if we 

   10       // create instances and call GC in same method, objects would 

   11       // technically still be associated with running code and would 

   12       // therefore not be eligible for garbage collection

   13       InitializeObjects();

   14 

   15       // suggest GC that now would be a lovely time to pick up the trash

   16       GC.Collect();

   17 

   18       Console.ReadLine();

   19     }

   20 

   21     private static void InitializeObjects()

   22     {

   23       // Create an object, and then set its value to null.

   24       // object's Dispose()-method is not called

   25       DisposableObject object1 = new DisposableObject { ObjectID = 1 };

   26       object1 = null;

   27 

   28       // Object's Dispose()-method is called right after we exit the using block

   29       using (DisposableObject object2 = new DisposableObject { ObjectID = 2 })

   30       {

   31 

   32       }      

   33     }

   34   }

   35 }

Here's the class that implements the IDisposable interface, and shows the use of Dispose()-method and destructor.

    1 using System;

    2 

    3 namespace DisposeTest

    4 {

    5   public class DisposableObject : IDisposable

    6   {

    7     public int ObjectID { get; set; }

    8 

    9 

   10     // this method is called when object is disposed, 

   11     // like after using-block

   12     public void Dispose()

   13     {

   14       Console.WriteLine(

   15         "Object {0} says: I've been disposed!", ObjectID);

   16     }

   17 

   18     // this method gets called when object is garbage collected

   19     ~DisposableObject()

   20     {

   21       Console.WriteLine(

   22         "Object {0} says: Argh, garbage collector got me!", ObjectID);

   23     }

   24   }

   25 }

Further reading in MSDN: IDisposable.Dispose Method