macOS "Cocoa Programming For Mac OS X" Chapter 14 Challenge

JGoose said:

Could someone please help me out with this? I'm not sure what Hillegass means he says the program "gives up its active status."

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I think it means your app lost focus, as in you switched to another application.

JGoose said:

I entered this into MyDocument.m but it doesn't work. What's wrong?

Code:

- (void) applicationDidResignActive: (NSNotification *) aNotification
{
	NSBeep();
	NSLog(@"Notification applicationDidResignActive:");
}

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As Chown noted above, it's an exercise to make sure you understand Hillegass, not always the easiest thing to do.

1) Make sure you add the correct (extra!) code when you have registered as an observer. ( Go back an look at page 213, in the init.)
Clue: need to add another addObserver:selector:name: object

Then it should work.

Why would this work there, while applicationDidResignActive: does not. And neither does windowDidResize: work in AppController.

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If my understanding of this is correct, it is because AppController is **NOT** a delegate in the true sense of the word. The delegate is the connection made in IB. AppController is simply adding methods to observe during the init. I **think** you have to add each notification you wish to observe, in this case.
But, I am sure others will chime in if this is incorrect.

chown33 said:

If I'm reading what you wrote correctly, you seem to think there's only one delegate in the entire app. This is incorrect. Delegation is a pattern: it identifies a relationship between two objects. That pattern is used in many different classes, to accomplish many different things.

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Hi Chown,
Well...maybe my understanding is not full yet. But, as i understand it, a single object can only have one delegate. So, if you set ObjectB as a delegate of ObjectA ( in IB), and *then* you wish to make ObjectC respond to certain notifications of ObjectA, you cannot make ObjectC a delegate of ObjectA as well, but you **can** register ObjectC with the notificationCenter to receive notifications for those changes you are interested in?? If this is not correct, and it may well be, then I would like to hear your input, as this seems to be the case as described by the OP.

Part of the confusion here is that Hillegass gives a really obfuscated explanation of delegation and notifications on page 213. Here is what he says.

If a standard Cocoa object has a delegate and posts notifications, it is automatically registered as an observer for the methods the object implements. If you are implementing such a delegate, how would you know what to call the method.

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I assume that both *it* and *the object* refer to the delegate.

The problem is that prior to this sentence, he was talking about adding observers, so one does not assume he has suddenly changed track. If one looks at the book's site, quite a few are confused by this, ( maybe even including me ) So, the challenge would seem to indicate that all one needs to do is simply implement the method, and it should work. I have not done this exercise in a while, but the OP is correct in that the AppController was indeed made a delegate of "file's owner" which in this case was NSApplication. So, going by the logic of the previous discussion, it would seem to indicate that simply implementing the methods *should* be the only things needed. Interested in your input, before I go back and redo the exercise.

But both applicationDidResignActive: and windowDidResize: are Notifications, right? So shouldn't they both only work in a delegate (that is if you don't use addObserver: selector: name: object: ), which in this case is AppController, and not MyDocument.

So my question is what is the difference between applicationDidResignActive: and windowDidResize: that they behave contrary to what I just said?

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I went back and redid these exercises...it's a little easier the second time round. To answer your specific questions.

AppController was made a delegate of NSApp and thus all notifications sent by NSApplication will **ONLY** be responded to by methods implemented in AppController. Hence, NSBeep() will only work if it is in the AppController...as you discovered. windowDidResize is a notification of NSWindow, and if you look where the delegate of the Window is, ( in IB) you will see it is File's owner, which you already know is "MyDocument". So, resizing will only be responded to by methods in MYDocument, and not in AppController.
Hope that helps.