Observing a Key in PDFView

Question

Hi,
I have a PDFView in my application, and I want my controller class to be notified when the user zooms in or out. I'm a Cocoa beginner, but I should be able to use key-value observing in this case. I have thus implemented the following two methods in my controller:
- (id)init
self = [super init];
[pdfView addObserver:self
forKeyPath:@"scaleFactor"
options:NSKeyValueObservingOptionNew
context:NULL];
return self;
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context
NSLog(@"changed!");
Unfortunately, this doesn't seem to work. observeValueForKeyPath is never called. Am I doing something wrong?
Thanks,
Alex
EDIT: I moved the addObserver code to a method that is called when the user presses a button. Funnily enough, it works now. Why can't I call addObserver from the init method?
null

Answer 1

First of all, your init method is not standard, you should test if the return value of [super init]; is valid:
- (id)init
if(self = [super init])
// your init code
return self;
And then, I think the problem comes from the fact that when the init method is called, other instances of the nib are not.
So, to solve this problem, you simply put your code into the -awakeFromNib method, this message is sent to every instance contained in the Nib file when it finished to initialize it, which means that all IBOutlet are considered as valid.