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RE: [DotGNU]lesson in dispose

From: David Podhola
Subject: RE: [DotGNU]lesson in dispose
Date: Sat, 15 Nov 2003 20:49:41 +0100

At least in Microsoft .NET the documentation 

When implementing this method, objects must seek to ensure that all held 
resources are freed by propagating the call through the containment hierarchy. 
For example, if an object A allocates an object B, and object B allocates an 
object C, then A's Dispose implementation must call Dispose on B, which must in 
turn call Dispose on C. Objects must also call the Dispose method of their base 
class if the base class implements IDisposable.


If an object's Dispose method is called more than once, the object must ignore 
all calls after the first one. The object must not throw an exception if its 
Dispose method is called multiple times. Dispose can throw an exception if an 
error occurs because a resource has already been freed and Dispose had not been 
called previously.

IMHO it should be implemented the way you suggest - the question remaining is, 
if it could not be done somehow magically automatically? :-)

David Podhola

-----Original Message-----
From: Neil Cawse [mailto:address@hidden 
Sent: Saturday, November 15, 2003 8:33 PM
To: Rhys Weatherley
Cc: address@hidden
Subject: [DotGNU]lesson in dispose

Can you tell me if Im on the right track here with regards to disposing managed 
resources. Take for example toolbar which uses imagelist, which uses 
ImageList.ImageCollection, which uses Image etc..
Is it a "rule" that we should implement IDisposable if we have any local 
objects who in turn implement IDisposable. And then we have to call their 
Dispose method when ours is called?
Do we just leave finalizers?

Is this correct?

protected override void Dispose(bool disposing)
            if (disposing)
                        if (imageList != null)
                                    imageList.RecreateHandle -= new 

In ImageList:
protected override void Dispose(bool disposing)
public void Dispose(bool disposing)
            images.Dispose(); // instance of ImageList.ImageCollection

In ImageList.ImageCollection:
internal void Dispose()
            if (images == null)
            for (int i = 0; i < images.Count; i++)
                        (images[i] as Image).Dispose();


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