"all kinds of global variables" is exactly the problem. Moreover, you've noticed, that it is very difficult to use the NodeView or MapView for example to display some example nodes in the format menu (an idea, which should be realised, IMHO). One reason for this is, that nearly every class of FreeMind needs all other classes to work - called "tight coupling", AFAIK.
But the best code originates IMHO from lose couplings - a class needs only itself and a hand ful of helpers that register at instanciation time or later. These helpers are decoupled by interfaces and their implementations. Only with this "ansatz", the software can be tested on module level and parts of the software can be reused.
I'm going to try to realize more of this decouplings in the future (I've already started, if you look at some of the new dialogs (perhaps the script editor), which can be tested stand-alone).
But a pair that belongs always together is a MapModel and a ModeController. (This answers the last mail of Dimitry). If we have only one ModeController (per mode or globally), the controller is not aware of the model it controls. He is stateless. But then, he isn't able to control the model, as there are states in the controllers (I'm thinking of different states like: node, free node or picture selected, menu states, and if I would have more time, I would think of more). IMHO, there is no advantage (except saving some 200Bytes for each instance of a controller) having only one, because you have that every action of a controller has to ask: to which map do I belong currently? And you have more problems to have parallel controller actions in the background of several nodes currently not displayed in the active map. Well, the mail is long enough now, I think.
-------- Original-Nachricht --------
Datum: Wed, 28 Nov 2007 11:06:40 -0500
Von: Ray Benjamin <firstname.lastname@example.org>
Betreff: Re: [Freemind-developer] FreeMind 0.10.0
I confess, I'm also puzzled about your dislike of singletons. Used
properly, they can be very useful. Do you have objections about their
use in specific circumstances, or in general? If it's in general, I'm
interested in understanding why. It's quite possible that I'm behind in
current thinking about their use, and I'm always interested in learning
I've certainly seen places where singletons have been abused, which can
lead to big problems, since some people treat them as permission to
establish all kinds of essentially global variables. I've found them to
be pretty useful, as long as I only used them where they fit the problem
I was trying to solve.
Dimitry Polivaev wrote:
first of all, when I write "singletons" I mean that we do not need
multiple instances of the mode controllers with corresponding actions
and listeners. It does not mean that the classes should implement the
singleton pattern. But I do not see any preferences of creating all
those objects each time we create a new map view or load a new map.
Further I have read that you do not like the singletons. But I still do
not see what you find wrong about them. I have to admit that I can not
follow you and understand you properly because you neither explain what
you mean nor tell me any arguments. I am even not sure, whether you
think that we need many controller instances and what reasons you could
have for it. So if you want that I understand you and come to you, you
could write a bit more.
Your appeal to read "good literature" does not make your position any
bit clearer either. But if you like to recommend me some good book, you
can always do it.
as I already anounced, I don't support more singletons. Please read
any good literature on MVC pattern and you'll see that none of them
needs any singletons to be successful.
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