Why not use a initialization NavigationSettings class for your
Navigation that has its own methods that can be interrogated by your
controller? ie - new Navigation(new NavigationSettings(params));
The "controller bar" could access the NavigationSettings instance to
find out its necessary settings.
IMHO, patterns are only useful where they actually solve problems,
not create additional ones. "Pattern Fever" does no good for
anyone.If you can't find a pattern that fits your requirements, maybe
patterns are the wrong way to go about it. You shouldn't need to
twist your requirements to try and fit into a particular pattern.
Hope this helps.
On 10/10/2006, at 4:31 AM, Matt Garland wrote:
I have a design problem:
A site I'm working up has a shell/module structure. Each module
composes an instance of a Navigation class.
This instance mixes and matches various navigation functionality.
Some modules might have last/next methods, some might have last/
next and direct goto (buttons) methods, some might have just goto
(buttons), or buttons and browser-like, history-based forwards/
backwards methods. Some will have pause/play. Some might have no
navigation at all. All would have an index property and an abstract
"goTo" method, which would be handled/implemented by the module
itself.
When the module is focused, a controller bar in the shell redraws
itself according to the module's navigation.
Here's two questions:
1) How do I make this navigation object? It mixes and matches a set
of methods almost randomly. It this even a candidate for a class?
Having just read Head First Design Patterns, my first thought was
that decorator could help. But how do you access added methods if
the basic object is wrapped more than once:
NextLast(History(new Navigation())).goBackward() wouldn't work
because goBackward is not a method of the outermost wrapper, NextLast.
Should I then make the decorator specify ALL possible methods? That
seems perverse.
Instead, it would be easier to supply a full-fledged navigation
object and selectively enable parts of it. But then the class would
turn into a mess of conditionals:
function next() {
currentIndex++
if (this navigation instance has a history) {
history.push(currentIndex);
}
This is stumping me. Having pattern fever (I recommend the book),
the only alternative I can think of is: turn each piece of
navigation functionality into a class (history, nextLast, etc),
then compose a navigation object as an array of objects, which
would each in term handle a message from the controller in the
shell (chain of responsibility?).
2) Once I manage to compose a navigation object, how can the
shell's controller bar interrogate it? That is, how to know which
methods are defined or enabled for it? Is there a more direct way
than looping through the object and looking at its properties and
methods (and since I'm doing this in AS3, I'm not sure I can even
do this). I suppose I could store a bunch os strings for
verification, but as with the last problem, I can't believe that
smarter programmers haven't solved this problem in an better way.
I should say that the site is mine and the only constraint is the
spec I'm giving myself, which is: give every module a navigation
module, so that the module's navigation will be easy to create (new
History(new Navigation)), without having to create a bunch of new
classes (HistoryNextLast extends History). In addition, I want the
the navigation object to refer back to other navigations objects so
that they form a XML-like nodal structure. This would be convenient
for retrieving navigation information, but even more for creating
an easy add-on structure. Basically, I want any combination of nav
functions to be able to lead to any other kind of combination,
module after module. How to achieve this I don't know yet.
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