[Wes]

Is there a simple-ish way to create a multiple window app with multiple window controllers that can communicate with each other? I have read Apple's documentation on document-based applications, and understood very little. Plus, in the program I am writing I have no need to open or save files off of the hard drive (or print etc...), but I do need multiple windows and being able to have those different windows controlled by separate controllers would save me a lot of headaches. I have this one window thing down pretty well, but multiple controllers throw me. Ideas?

[Chuckit]

You're going to have to explain more fully, because with just the requirement "multiple window controllers communicate with each other," I would say to create several custom window controllers and have them either keep references to each other, use the responder chain or send notifications — the same way any other objects communicate with each other. But I reckon you must have some more specific problem in mind than this.

[techtrucker]

Wes,

When I first started learning Cocoa/ObjC I struggled with what you're describing. Take a look at /Developer/Examples/InterfaceBuilder/SimpleMultiWindow or a dated example on my .mac site:

http://homepage.mac.com/stevewoodward/FileSharing4.html

TwoWindow.zip may be enough to get you started. But there are several ways to attack the problem. In the case of one window calling another you could just use setParentController, but if they're all called separately then you need a "centralized" method of communication, such as notification centers.

Steve W

[Earth Mk. II]

The "right way" to do that would be to use notification centers, and perhaps a more general controller class or two depending on what type of data you want to share between window controllers and what you want that data's life span to be. (the other controllers can also handle things like data verification and persistence in a centralized way)

Alternatively, you could try to make each window controller hold a reference to each other window controller. This would be easier to set up initially, but will be major pain in your ass to maintain, especially if the application's complexity grows (and trust me - it will).

[techtrucker]

Earth Mk. II is right about notification centers. The application I'm working on right now is rather complex and I am basically doing what he cautions against, havng the window controllers hold references to other window controllers. Im my case it's not too bad, but I can see where it could become unweildy. This app is basically a database app where one window will be a "browse" window with a table view, and will call up a second window to let the user edit the data for the selected row. (Long story why I can't let the users edit the data in the table directly). So I've got Window 1a calling up Window 1B, Window 2A calling up Window2B, etc. The two windows need to communicate data back and forth and I do that by having them reference each other's controllers and heavy use of accessor methods.
So it really depends on the needs of your specific application, if you could clue us in on the details maybe we can steer you in the right direction.

Steve W

[djohnson]

Ahh but Notifications are slow. I am guessing you want window A to call a function in window B, etc. Why not just setup an outlet? IE:

IBOutlet id windowAConn;

In IB, just have a new outlet and connect it to the other window controller. I have done this in many projects... SetiLogger X uses multiple windows and they can all talk to each other. Email me at djohnson(at)tfworld.com for more info and some code examples.

[Chuckit]

Originally posted by djohnson:
Ahh but Notifications are slow. I am guessing you want window A to call a function in window B, etc. Why not just setup an outlet? IE:

IBOutlet id windowAConn;

In IB, just have a new outlet and connect it to the other window controller.

It's not very elegant, though. I mean, it works, but it requires a lot of classes to be exposed to each other, and anytime that class hierarchy changes in any way, you're going to have to reconfigure everything.

I suppose if algorithm speed is that important, yeah, notifications would be a problem, but that's only if the window controllers need to send each other messages hundreds of times a second.

[techtrucker]

In a two window situation I let window A and B reference each other. Anything more than that and I usually go with a notification center. I haven't seen any performance hits, but I'm not passing a lot of data back and forth. Not exactly subscribing to the MVC school of thought, but I'm trying...

Steve W

[11011001]

I ran into this problem with a very complex Java program that we had to write for an assignment. We ended up using property change listeners to solve this problem.

For Java is there anything like notification centers? How would one approach this problem in Java?

[techtrucker]

A long time ago I went looking for something like notification centers in Java and had bookmarked this but never used it:

http://www.amug.org/~glguerin/sw/not.../overview.html

Steve W

[Chuckit]

That looks more similar to CFUserNotification than NSNotification.

[Earth Mk. II]

Originally posted by 11011001:
I ran into this problem with a very complex Java program that we had to write for an assignment. We ended up using property change listeners to solve this problem.

For Java is there anything like notification centers? How would one approach this problem in Java?

I suspect that NSNotificationCenter works rather cleanly because of selectors, and I don't know if there's anything equivalent to those in Java.

If there is, you could set up a hashtable with a key for each observed notification, then an array of observing objects (along with the method to perform) as the associated object.

When a message is passed into the center, check it's name against the table - if there's a hit perform all the requested objects in the array, if not.. ignore it.

It would be a very basic implementation of the concept. But it should work, provided there's a way to perform arbitrary methods on java objects.

[EDIT]

you might want to check out Apple's NSNotificationCenter (Java) documentation and see what you can grok from it.