I have a document-based app with the recommended NSDocument / NSWindowController setup. Every window has its own NSWindowController instance and an associated XIB file. The interface is loaded pretty straight-forward in -(id)init: if (self = [super initWithWindowNibName:#"DocumentWindow"]) { // yadda yadda }. The XIB file contains an object that represents a separate controller that should be instanciated every time the user opens a new window. It presents data that is only relevant to the current document. When I unpack the object with -(id)initWithWindowNibName: I always get a reference to the same instance despite having two different window controllers and despite having called -(id)initWithWindowNibName: twice. The XIB loading mechanism seems to only unpack the same archived object once which kind of makes sense (really?).
Is there no way besides allocating separate objects in code, manually loading views, calculating their sizes, adding them as subviews, then setting bindings and keeping an eye on unbinding them manually when the window gets closed?
I’m banging my head against the wall, because of my own stupidity. It just makes things worse.
As I initially thought I was absolutely on the wrong path. The issue was simply that I registered a notification in the aforementioned instantiated class for an object that was a subview of the application’s keyWindow (I hacked it together and wanted to change it later to a property, ouch). When the application was loaded all instances registered for all document windows and all of them got notified and calculated the same data.
The debugger is my best friend today.
There is actually nothing like an optimization when you unarchive objects from a XIB and you will always get different instances (which absolutely makes sense in retrospect). If you encounter a similar issue, then it’s probably an unrelated bug at another place in your code.
Related
Unannounced, the 2 notices in the image below were discovered while searching for why -applicationShouldTerminate: is not being called in AppDelegate.m on quit (Cmd+Q). It worked some time ago.
Hovering over the two yellow triangles reveals:
NSObject does not have an outlet named delegate.
The action 'terminate:' is not defined on 'NSObject'.
Xcode is not showing errors or warnings and the app builds.
-applicationShouldTerminateAfterLastWindowClosed: IS called within AppDelegate.m when the red dot of the window is clicked.
My experience with Cocoa is thin (learning). I've compared the connections for File's Owner, Application and App Delegate in 2 other projects, and think a missing window outlet might be the cause. The notices above point to something else.
I would like to make sure the connections are correct as a first step. How do I repair this?
Edit: Add image of Main Window Controller connections
Edit 2: Add image of File's Owner connections
In the main NIB of an application, the two placeholders, File's Owner and Application, both end up referring to the same object. That object is the application object, the sole instance of NSApplication or a custom subclass of it. The Application placeholder is always holding the place of the application object because that's its purpose. The File's Owner placeholder is holding the place of whatever object is specified as the NIB's owner when it is loaded at run time. When Cocoa loads the main NIB at application startup, it specifies the application object as the owner. For other NIBs, File's Owner will likely be some other object.
However, Interface Builder doesn't know that a given NIB is the main one. So, it treats those two placeholders independently.
I don't know why Interface Builder has taken to setting the class of the Application placeholder to NSObject. It should really be NSApplication. That's why Interface Builder doesn't realize that the application object has a delegate outlet and an action method -terminate:.
As it happens, the class of File's Owner is properly set to NSApplication.
So, there are two ways to fix this:
Set the class of the Application placeholder to NSApplication or, in the rare case that you're using a subclass, that subclass.
Disconnect those connection from the Application placeholder and connect them to File's Owner instead. This is the way that the standard project templates do it.
For any given main NIB, you should probably standardize on using one or the other but not both. That is, one or the other should have no connections. That way you avoid conflicting or redundant connections.
Sorry for the stupid post, but I am new to Objective-C programming and Cocoa and have a couple of questions which I can't find the answers to, I'm hoping someone can enlighten me.
Firstly, in XCode, when using the Interface builder, when I want to create a new object I drag the object to my 'assets'. However I can't specify methods or anything without manually creating a new class file. Is there any point using the interface builder's 'object'?
The first app I built to test things with, I put most of the code in the AppDelegate class files. Research has shown me that the AppDelegate's purpose is simply handling application events like launching and closing. Was I wrong in putting the methods in this class? Does it make any difference?
Finally, if I have several class files created, each handling their own functionality with an interface built and linked to the classes, then what do I do with the 'main' file? It seems to me that the 'main' file and 'appdelegate' class files will be for the most case left as-is?
I hope that makes sense. Again i'm sorry for the silly-sounding questions but I can't find any answers.
Thanks in advance everyone!
Firstly, in XCode, when using the Interface builder, when I want to create a new object I drag the object to my 'assets'. However I can't specify methods or anything without manually creating a new class file.
Sure you can. Just set the class of the object using the inspector.
Note that you can only connect nib objects to an outlet or action. You can't specify any random methods, nor should you—the whole point of the IBOutlet, IBOutletCollection, and IBAction keywords is to declare in code that these properties/methods are used by a nib.
Is there any point using the interface builder's 'object'?
Yes, but pretty rarely. Usually you create objects in code and connect outlets to them.
The application's delegate is one object you may want to create in the MainMenu or MainWindow nib, if you build your application that way (the iOS templates have changed away from it for some reason).
The first app I built to test things with, I put most of the code in the AppDelegate class files. Research has shown me that the AppDelegate's purpose is simply handling application events like launching and closing. Was I wrong in putting the methods in this class?
Probably. The application's delegate generally should only handle business relating to the NS/UIApplicationDelegate protocol.
On the flip side, it's OK to make your root view controller the application's delegate, if it makes sense to do so (and the NS/UIApplicationDelegate implementation code is not too voluminous). The question you have to answer—and only you can answer it for your application—is whether you are making your root view controller the application's delegate or the application's delegate the root view controller. If in doubt, keep them separate.
Does it make any difference?
Long-term, yes. It's very easy, especially in the class of the application's delegate, to create a Big Ball of Mud class—one without well-defined and clearly-delineated responsibilities. Take dynamite to such a class as soon as possible.
Finally, if I have several class files created, each handling their own functionality with an interface built and linked to the classes, then what do I do with the 'main' file? It seems to me that the 'main' file and 'appdelegate' class files will be for the most case left as-is?
Yes. They're boiler-plate.
If you haven't written any code in the application's delegate (or have removed everything you had put there into new and better-delineated classes), such that all that's left are empty method bodies or none at all, you can safely remove the application's delegate. You can always create it again later if you change your mind.
Note that if you delete your application delegate class, you should also change the main.m file—or the MainMenu/MainWindow nib, if you have one—to not refer to it. Your application won't build if your UIApplicationMain call (or any other code) refers to a class that doesn't exist, and it will crash if your MainMenu/MainWindow nib (or any other nib) refers to a class that doesn't exist.
There is no shame in your application having a delegate if you need it to, but if you don't, removing it and the class you were using for it eliminates future temptation to stuff code there or use it to store third-order globals.
The point of using objects in interface builder is to connect methods of the object to UI elements.
It partly depends on what your methods are doing, but for the most part the app delegate class is going to be left alone. It isn't an actual requirement (your program will work either way) but it is common practice because it generally creates more maintainable code. The app delegate should just handle the application events ( using other classes to do any complex logic or heavy lifting ).
The 'main' file will most likely not change. I can't think of any reason to do so, but I wouldn't rule it out for some advanced cases.
To be honest I only used the Object thing in IB once, when I wanted a separate object to have some UI bindings.
About the app delegate and main file, yes, you'll leave them as-is most of the time. But if you try to do something besides test apps you'll need to handle open events to, for example, connect to a server, ask the user for a review, increment some launch counter, etc... Those are just examples!
The main file I advise you to left it alone and use the object oriented tools provided. You should have a view controller hierarchy, isolate your views from the data, and use the view controller to comunicate between view and model. Read about MVC if you want more info on how your application should be organized.
I have a XIB file with my controls in it, loaded in the Interface Builder (Xcode 4.0.2 on Snow Leopard).
The file's owner is set to, let's say, the someClassController class, and I've also added (in the Interface Builder) an NSObject instance of someClass, as well.
I've managed to link e.g. a button with an action in someClassController or someClass - and it works for both of them.
However, whenever I link an outlet to ANY of them, it fails to show up; and NSLog reports NULL pointers.
Hint : My issue here could be much more complicated than it seems, since both my someClass and someClassController classes inherit other classes, which inherit other classes and so on (I'm dealing with a huge-to-chaotic codebase, and I don't really know what else could be helpful to post)... However, I would still like to hear your opinion on what might be going wrong in such a case...
When you see problems like this, it's almost always because you have more than one object of the kind that has the outlet. The one in the nib whose outlet you connected is not the one that is examining its outlet.
To investigate this, add statements in the object's initializer method(s) and possibly awakeFromNib to log the value of self.
Some (or all, or none) of the objects may be created in nibs, and some (or all, or none) of them may be created in code; objects in the latter group won't trip awakeFromNib, since they didn't.
Either way, once you've inventoried what instances of the class you have, you can kill them off until you're left with the ones you want.
To add to Peter Hosey's answer, and after reading some more details in the other question you posted about this issue, here are some other factors to consider:
The File Owner class selected in the nib is completely ignored at runtime. It's there only for design-time convenience – for checking available actions and outlets.
Is there any chance you're finding nil pointers in -init? Outlets are connected after -init and before -awakeFromNib. They'll never be connected in -init.
I'm trying to understand the sequence of initialization (from your other post). It sounds like you are creating a new instance of your CTTabContents subclass, and passing it to your CTBrowserWindowController subclass's -addTabContents: method. Then the CTBrowserWindowController loads your objects from the nib.
Or, maybe that's wrong. You might be creating a instance of your CTTabContentsController subclass. Then that object is loading TabContents.xib.
It's important to track down where the nib is being loaded and which object is being provided as the file owner at that time.
Another question: are you using manual release/retain, automatic reference counting, or garbage collection?
Finally, I reiterate the importance of printing out the self pointer in your initialization methods. In addition to -init and -awakeFromNib, try other initialization methods like your CTTabContents subclass' -initWithFrame:. When you're discovering intermittent null pointers in the rest of your debugging, print out the self pointers then, too. You'll probably be seeing different values of self then, too.
I have a working app with a navigation controller, two view controllers, two views, a model object, and no xib file. The views are created programatically. Now I'd like to build the same app using IB and xib files. Does anyone know of a writeup that explains how to add xib files and delete the program statements they replace? If not, then something that discusses the equivalences between xib library elements and program statements?
Why do I want to do this? Because I'm trying to understand what xib files do and how they interact with program statements and I thought this would be a good learning exercise. I made one try at it but couldn't get it to compile. In fact, every time I use xib files, except following textbook examples, I get hopelessly tangled up in code that won't compile or doesn't work if it does compile. So I must have some basic misconception. I need to figure out what xib files are doing behind the scenes. They seem potentially very powerful but I won't use them if I don't understand what they're doing.
I read elsewhere in stack overflow that they are a serialized version of a compiled view (or something like that). I understand that conceptually. I'm thoroughly familiar with Python's pickle files. But that doesn't explain much in practice.
A nib/xib contains the information needed to create and connect objects together. Basically, it contains instance variable and class information for the objects it contains. To load one, you use the UINib class (NSNib in Mac OS X), or the NSBundle loadNib… methods. NSBundle's methods are easier to use, and I would suggest using them unless you will load a nib several times. For iOS, you would typically use [[NSBundle mainBundle] loadNibNamed:#"NibNameWithoutExtension" owner:self options:nil];. The owner does not have to be self. It is the object represented by the "File's Owner" object in IB and will receive any connections made to that object. The options parameter can be used to get the top level objects in the nib, but you usually use outlets instead. When a nib is loaded, the objects inside it are allocated and instantiated (using initWithCoder:), and connections are created using setter methods, or by setting the instance variables directly.
I am currently working through the famous "Cocoa Programming for OSX" by Aaron Hillegaas.
In Chapter 12 he wants me to create an about window using
[BOOL] successful = [NSBundle loadNibNamed:#"About" owner:self];
which, by itself, works perfectly well. However, I am using the garbage collector and since I do not retain a pointer to that about window, it is garbage collected and thus disappears after a second or two. It works perfectly well if garbage collection is disabled.
Is there a way to create a window without holding a pointer to it and without having it eaten by the garbage collector?
You can retain the window with CFRetain, or use NSGarbageCollector's disableCollectorForPointer:. However, you can easily introduce a memory leak. Make sure whichever action you use to close the window also releases the window.
If the sender passed to the close action inherits from NSView, it will have a window property that you can use to get a pointer to the window.
However, this is not how Cocoa is designed to work. In Chapter 12 of Hillegaas' book, he has this to say:
When sent showWindow: for the first time, the NSWindowController automatically loads the nib file and moves the window on screen and to the front. The nib file is loaded only once. When the user closes the [window], it is moved off screen but is not deallocated. The next time the user asks for the [window], it is simply moved on screen.
If you deallocate the About window, your app will either crash or appear not to respond the second time someone opens it.
Edit: An alternative (but one that doesn't give you practice in loading nibs) is to add the About window an an NSWindowController to the main nib (make sure you uncheck the About window's "Visible At Launch" attribute). This makes a mess of Main.nib, but can be done entirely in Interface Builder. Connect:
the About controller's window outlet to the About window
the About controller's showWindow: action to the About menu item
if you've your own close button in the About window, connect it to the window's performClose: action.
As for how advisable this course is, Apple has this to say:
A very simple application might be able to store all of its user interface components in a single nib file, but for most applications, it is better to distribute components across multiple nib files. Creating smaller nib files lets you load only those portions of your interface that you need immediately. Smaller nib files results in better performance for your application. They also make it easier to debug any problems you might encounter, since there are fewer places to look for problems.