Dispose and Finalize in C#

Dispose: The following rules outline the usage guidelines for the Dispose method:

• Implement the dispose design pattern on a type that encapsulates resources that explicitly need to be freed. Users can free external resources by calling the public Dispose method.
• Implement the dispose design pattern on a base type that commonly has derived types that hold on to resources, even if the base type does not. If the base type has a close method, often this indicates the need to implement Dispose. In such cases, do not implement a Finalize method on the base type. Finalize should be implemented in any derived types that introduce resources that require cleanup.
• Free any disposable resources a type owns in its Dispose method.
• After Dispose has been called on an instance, prevent the Finalize method from running by calling the GC.SuppressFinalize Method. The exception to this rule is the rare situation in which work must be done in Finalize that is not covered by Dispose.
• Call the base class's Dispose method if it implements IDisposable.
• Do not assume that Dispose will be called. Unmanaged resources owned by a type should also be released in a Finalize method in the event that Dispose is not called.
• Throw an ObjectDisposedException from instance methods on this type (other than Dispose) when resources are already disposed. This rule does not apply to the Dispose method because it should be callable multiple times without throwing an exception.
• Propagate the calls to Dispose through the hierarchy of base types. The Dispose method should free all resources held by this object and any object owned by this object. For example, you can create an object like a TextReader that holds onto a Stream and an Encoding, both of which are created by the TextReader without the user's knowledge. Furthermore, both the Stream and the Encoding can acquire external resources. When you call the Dispose method on the TextReader, it should in turn call Dispose on the Stream and the Encoding, causing them to release their external resources.
• You should consider not allowing an object to be usable after its Dispose method has been called. Recreating an object that has already been disposed is a difficult pattern to implement.
• Allow a Dispose method to be called more than once without throwing an exception. The method should do nothing after the first call.

  Finalize:The following rules outline the usage guidelines for the Finalize method:

• Only implement Finalize on objects that require finalization. There are performance costs associated with Finalize methods.
• If you require a Finalize method, you should consider implementing IDisposable to allow users of your class to avoid the cost of invoking the Finalize method.
• Do not make the Finalize method more visible. It should be protected, not public.
• An object's Finalize method should free any external resources that the object owns. Moreover, a Finalize method should release only resources that are held onto by the object. The Finalize method should not reference any other objects.
• Do not directly call a Finalize method on an object other than the object's base class. This is not a valid operation in the C# programming language.
• Call the base.Finalize method from an object's Finalize method.

// Design pattern for a base class.
public class Base: IDisposable
{ //Implement IDisposable.
public void Dispose() {
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing) {
if (disposing) {// Free other state (managed objects).}
// Free your own state (unmanaged objects).
// Set large fields to null.
}
// Use C# destructor syntax for finalization code.
~Base(){// Simply call Dispose(false).
Dispose (false);
}
// Design pattern for a derived class.
public class Derived: Base{
protected override void Dispose(bool disposing) {
if (disposing) { // Release managed resources. }
// Release unmanaged resources.
// Set large fields to null.
// Call Dispose on your base class.
base.Dispose(disposing); }
// The derived class does not have a Finalize method
// or a Dispose method with parameters because it inherits
// them from the base class.}