Question

When I try setting up observation of this specific key, nothing happens. Here is what I mean.

I have a standard Cocoa application, with an NSTableView, and I figured out how to change the image shown in an image view based on what cell was selected.

Now, I am trying to figure out how to disable/enable buttons by the selected index. What I mean by this, is that I have a button in the window, that is disabled on certain indexes.

SomeClass’s init method

-(id)init {
    if (self=[super init]) {
        [arrayController addObserver:self forKeyPath:@"selectionIndex" options:NSKeyValueObservingOptionNew context:NULL];
    }
}

However, when I implement the observeValueForKeyPath: method, the changes are not being picked up as I pick new indexes. As a matter of fact, the outlet shows (null) if I try logging it. However, when I add the observer in AppDelegate, AppDelegate (when specified as the observer) picks up changes.

Is there some reason my generic SomeClass object does not? Should it be done a different way?

NOTE:

I tried subclassing SomeClass as a NSWindow, then making the window’s owner SomeClass, and setting up the observer in awakeFromNib, and this works, but seems like a bad way to do it.

Answer 1

The init method happens too early in the process, before the outlets are connected (I think). Putting the code in awakeFromNib will work correctly. This is from Apple’s docs in the NSObject class reference:

The nib-loading infrastructure sends an awakeFromNib
message to each object recreated from a nib archive, but only after
all the objects in the archive have been loaded and initialized. When
an object receives an awakeFromNib message, it is guaranteed to have
all its outlet and action connections already established.