Re: [DUG] Discussion & Donation

[Todd Martin]

Well you said you wanted feedback, so I hope this isn't too picky.   1) I find the inconsistent use of variable prefixes a bit annoying. I tend to stick with F- class field A - method parameter P - pointer and no prefixes for class properties or local variables.   2) TListenerItem.FListener is redundant, since the information it contains is already held in TListenerItem.FBindMethod It could have been implemented as a function, but I don't see why it is needed. As usual, redundancy leads to complication elsewhere   eg.  if (MethodEquals(TMethod(Items[i].FBindMethod) ,TMethod(ABinder))) and (Items[i].FListener = AListener) then   the second condition is automatically satisfied by the first condition.   3) Why define a TNotifier class when all its methods are static? They could be defined as simple procedures/functions in the unit.   4) I'm not keen on the idea of passing a string parameter to identify the message type, for the simple reason that spelling mistakes can arise and you're never really sure at compile time what "messages" are being broadcast/handled. This problem can of course be ameliorated through the use of constants, but I prefer the use of an enumerated type.   Having said all that. I like the loose coupling of your solution. I have implemented the observer pattern previously with the lists maintained internally by the objects involved, so removing the need to inherit from a particular class is a great improvement. I hadn't considered that option before. Of course you do pay a miniscule performance penalty in having to find the correct list for the object. Perhaps the use of THashedstringlist could mitigate this further.   Todd.     ----- Original Message ----- From: Kyley Harris To: NZ Borland Developers Group - Delphi List Sent: Wednesday, May 10, 2006 3:36 PM Subject: [DUG] Discussion & Donation In an attempt to create some more interesting discussion, other than talking about the crud IDE issues, I am donating some useful code for discussion, rather than for help. Feel free to keep/use the code if you want to. Be mean if you feel the need (but if your personal then watch out ;) Hopefully this may introduce a discussion where people learn something, or are able to contribute some interesting ideas/information about the topic (which is object notification and observation).   In the attached zip is a sample application showing a basic, but horrible use of the class in uNotifier.pas. TNotifer is a class I wrote a long while back which loosely follows an observer pattern for allowing one-to-many observations between an object, and a bunch of interested object.   The main difference this class has between many observer patterns is that you do not have to modify existing classes, or sub-class anything, or instantiate anything in your existing objects. The TNotifier handles all the bindings, you just need to implement one listening event on each listening object.   The sample app is a corny app that makes child forms (button click) update a memo based on changes to the memo on the main form. God help me if I ever did anything as potentially unthread safe as that in a real app.   Fun fun fun . (I hope the app compiles. You never know with these tricky little sample apps) _______________________________________________ Delphi mailing list Delphi@ns3.123.co.nz http://ns3.123.co.nz/mailman/listinfo/delphi Internal Virus Database is out-of-date. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.5.1/327 - Release Date: 28/04/2006

Internal Virus Database is out-of-date.
Checked by AVG Free Edition.
Version: 7.1.385 / Virus Database: 268.5.1/327 - Release Date: 28/04/2006

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