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Topic: Storing function names in classes (Read 539 times) |
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Markavian
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Storing function names in classes
« on: Jul 9th, 2004, 12:10am » |
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I'm starting a new project, and predict I might have a problem.
I'm creating a menu class, which stores the text for menu items and a function name. At the moment I have set both up as strings.
Code:class cr_menu_item() {
// Constructor
void cr_menu_item(String text, String function) {
String text = text;
String function = function;
}
} |
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A separate class/function will build the menu out of these items and track rollovers. Is it possible to execute named functions based off variables?
i.e. variable function execution?
possible e.g.:
Code:/*?????
void cr_launch_website() {
// do stuff
}
String myFunction = "cr_launch_website";
run(myFunction);
?????*/ |
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I'll go check the reference, I don't remember seeing anything though.
Many thanks to anyone who can help.
Regards,
- Markavian
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arielm
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Re: Storing function names in classes
« Reply #1 on: Jul 9th, 2004, 12:53am » |
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java has a "reflection" mechanism which enable to invoke methods via string names, but generally it's a bit overkill (unless you code something like a javascript interpreter...)
for menu matters, you should take a look at how it's done within pure-java apps... the pattern is going like that:
- you have a "menu" object, with child menu-items.
- it's possible to "add a listener" object to "menu"
- each time a menu item is activated: "menu" is going over its list of "listeners" and is "casting an event" (e.g invoking a "menuSelected" method) with some kind of id, representing the item in question
- so... your "listener" object's menuSelected() method is called with an id as a parameter
- from here, it's a matter of using a switch-case construct or a series of if's (switch case is preferable when there's a lot of options, it only implies that the passed "id" is an int)
hth!
EDIT:
here's an home-made event casting system from my ttc work:
Code:public interface EventListener
{
public void event(EventCaster source, int message);
}
public class EventCaster
{
public Vector listeners;
public void addListener(EventListener listener)
{
if (listeners == null)
{
listeners = new Vector();
}
if (!listeners.contains(listener))
{
listeners.addElement(listener);
}
}
public void removeListener(EventListener listener)
{
listeners.removeElement(listener);
}
public void castEvent(int message)
{
for (int i = listeners.size() - 1; i > -1; i--)
{
((EventListener) listeners.elementAt(i)).event(this, message);
}
}
} |
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(ouch... word-wrapping is tough with this forum!)
that was for the structure, from here:
1) your Menu class should "extend" EventCaster
2) your MenuObserver class should "implement" EventListener
+ in the setup-part of your code, you should have something like:
myMenu.addListener(myMenuObserver)
then, inside your Menu class, when a menu-item (say, an item symbolised by MENU_CLOSED) is selected, it should go like:
castEvent(MENU_CLOSED);
(it implies that MENU_CLOSED is defined with an int value somewhere...)
and of course, inside your MenuObserver, you have something like:
Code:void event(EventCaster source, int message)
{
if (source == myMenu && message == MENU_CLOSED)
{
foo();
}
} |
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final note: the advantage of passing a "source" object in addition of a message/id, when casting an event is that the same "listener" gets the ability to respond to, say, different menu instances...
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| « Last Edit: Jul 29th, 2004, 3:35am by arielm » |
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Ariel Malka | www.chronotext.org
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Markavian
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Re: Storing function names in classes
« Reply #2 on: Jul 9th, 2004, 11:35pm » |
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Hi Ariel,
I generally understand what you are saying (after reading it through a couple of times), but I don't quite understand your code, how it will benefit me, or extending and implementing classes work.
I understand what you mean about creating classes for each menu containing the logic and actions, and using a generic class containing the code for detecting states in another class, but I'm not sure the examples you gave are quite appropriate for what I need.
If you could give some basic examples about extending classes, or some useful links; then we may have solved my problem by building my menu in a different way.
(btw: I've got some follow up work on TTC, but its not really ready at the moment)
Best regards,
- Markavian
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arielm
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Re: Storing function names in classes
« Reply #3 on: Jul 10th, 2004, 11:56pm » |
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on Jul 9th, 2004, 11:35pm, Markavian wrote:| I generally understand what you are saying (after reading it through a couple of times), but I don't quite understand your code, how it will benefit me, or extending and implementing classes work.) |
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lol... bah, forget this brutal eruption of java geekness (i'm coding too much these days!)
on Jul 9th, 2004, 11:35pm, Markavian wrote:| (btw: I've got some follow up work on TTC, but its not really ready at the moment) |
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cool!
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Ariel Malka | www.chronotext.org
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