Charlotte Foust
cfoust at infostatsystems.com
Tue Jan 13 19:16:56 CST 2004
John, Would you have understood your response when *you* were first getting your feet wet in this kind of programming? I wasn't trying to provide the definitive answer, just a frame of reference. VB/VBA isn't fully object-oriented, so it can't really support Implements in all its glory. Charlotte Foust -----Original Message----- From: John W. Colby [mailto:jwcolby at colbyconsulting.com] Sent: Tuesday, January 13, 2004 4:54 PM To: Access Developers discussion and problem solving Subject: [AccessD] Implements vs WithEvents Charlotte, >They have somewhat different purposes. No, they have completely different purposes. >Implements allows you to subclass an existing object/class and give it additional or different functionality, so you can have a class Dog and a subclass Spaniel that has a property Retriever. Well... true but not exactly. My issue with that statement is the term subclass as you use it. Yes you are subclassing the original but ONLY the interface. IMHO that is almost useless Implements is an interface ONLY inheritance, i.e. it allows (forces) you to start with the same public data and method DEFINITION but does not actually inherit the behaviors (methods) themselves. I.e. the code that runs in the class that is being subclassed is NOT inherited into the subclass. Access' inheritance (interface) is not very useful except as a template kind of thing. I find it useless enough that I personally don't bother. On the other hand Shamil is a proponent so it must have its uses. When you move to VB.NET (or any of the other .net languages I believe) TRUE inheritance is available. I.e. if you have a method with a thousand lines of code, when you subclass that object the new object inherits that code as well as the data. In our Implements subclassing, you would have to cut and paste that thousand lines of code into the subclass. Can you say maintenance nightmare? >You can intercept and respond to specific events when they happen in >the object. Did the Bark event trigger? WithEvents lets you find out and respond from another class/object. Exactly correct. One of the MAJOR shortcomings of Access / VBA (in fact VB prior to VB.Net) is that Inheritance is virtually non-existent, and even worse, objects other than forms don't have a built in class that you can get at to add functionality directly to. What WithEvents really does is allow you to build class wrappers for objects so that you can encapsulate behaviors (functionality) in your class. In essence you still have two objects, the control (or even another class or OCX) and your class, but now you can put all of the common functionality in your class along with the event stubs of the control/class/ocx that generates the event. This does not get you any further down the road towards inheritance, sadly it simply doesn't appear to be possible in Access / VBA. But it does provide a huge step up in encapsulation. John W. Colby www.ColbyConsulting.com -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com]On Behalf Of Charlotte Foust Sent: Tuesday, January 13, 2004 4:56 PM To: Access Developers discussion and problem solving Subject: RE: [AccessD] =function() in .onclick They have somewhat different purposes. Implements allows you to subclass an existing object/class and give it additional or different functionality, so you can have a class Dog and a subclass Spaniel that has a property Retriever. WithEvents allows you to monitor the events of an object/class. You can intercept and respond to specific events when they happen in the object. Did the Bark event trigger? WithEvents lets you find out and respond from another class/object. Charlotte Foust -----Original Message----- From: Robert Gracie [mailto:Subscriptions at servicexp.com] Sent: Tuesday, January 13, 2004 1:45 PM To: Access Developers discussion and problem solving Subject: RE: [AccessD] =function() in .onclick Hello All, Since I'm just learning this type of programming technique I thought I would ask a question... Why not use Implements instead of WithEvents? My limited understand of WithEvents is that they will not return functionality unit they (the event) has completed processing... Since I'm just at the "door" so to speak with learning how to use and incorporate these new (to me) programming techniques into my work, I really want to start out using the "best" technique... Robert Gracie www.servicexp.com _______________________________________________ AccessD mailing list AccessD at databaseadvisors.com http://databaseadvisors.com/mailman/listinfo/accessd Website: http://www.databaseadvisors.com