.NET Resource Management - Effective C# - page 100

But there are still holes in the mechanism you've created. How does a
derived class clean up its resources and still let a base class clean up as well?
If derived classes override finalize or add their own implementation of
IDisposable, those methods must call the base class; otherwise, the base
class doesn't clean up properly. Also, finalize and Dispose share some of the
same responsibilities: You have almost certainly duplicated code between
the finalize method and the Dispose method. As you'll learn in Item 23,
overriding interface functions does not work the way you'd expect. The
third method in the standard Dispose pattern, a protected virtual helper
function, factors out these common tasks and adds a hook for derived
classes to free resources they allocate. The base class contains the code for
the core interface. The virtual function provides the hook for derived
classes to clean up resources in response to Dispose() or finalization:
protected virtual void Dispose( bool isDisposing)
This overloaded method does the work necessary to support both finalize
and Dispose, and because it is virtual, it provides an entry point for all
derived classes. Derived classes can override this method, provide the
proper implementation to clean up their resources, and call the base class
version. You clean up managed and unmanaged resources when isDisposing
is true, and you clean up only unmanaged resources when isDisposing is
false. In both cases, call the base class's Dispose(bool) method to let it clean
up its own resources.
Here is a short sample that shows the framework of code you supply when
you implement this pattern. The MyResourceHog class shows the code to
implement IDisposable and create the virtual Dispose method:
public class MyResourceHog : IDisposable
{
// Flag for already disposed
private bool alreadyDisposed = false ;
// Implementation of IDisposable.
// Call the virtual Dispose method.
// Suppress Finalization.
public void Dispose()
{
Dispose( true );
GC .SuppressFinalize( this );
}