Hello,
in the app I'm writing, I have a custom view with several KVO-
compliant properties which, when changed, should cause the view to
redraw itself. I've then set up a dependent key (displayNeeded) and
have my custom view KV-observe changes to that key. When a change
happens, I call setNeedsDisplay. The relevant code appears below:
This is in the -initWithFrame: method of my custom view:
[self addObserver: self
forKeyPath: @"displayNeeded"
options: (NSKeyValueObservingOptionNew |
NSKeyValueObservingOptionOld)
context: NULL];
And these are the two methods that are needed to make KVO work for the
dependent key in question:
+ (void) initialize
{
[self setKeys: [NSArray arrayWithObjects: @"foo", @"bah", @"etc",
nil]
triggerChangeNotificationsForDependentKey: @"displayNeeded"];
}
(Yes, I know that -setKeys:triggerChangeNotificationsForDependentKey:
is deprecated in Leopard)
- (void) observeValueForKeyPath: (NSString *) keyPath ofObject: (id)
object
change: (NSDictionary *) change context: (void *) context;
{
id oldValue = [change objectForKey: NSKeyValueChangeOldKey];
id newValue = [change objectForKey: NSKeyValueChangeNewKey];
NSLog(@"old = %@", oldValue);
NSLog(@"new = %@", newValue);
if (! [newValue isEqual: oldValue])
{
if ([keyPath isEqual: @"displayNeeded"])
{
NSLog(@"displayNeeded");
[self setNeedsDisplay: YES];
}
else
if ([keyPath isEqual: @"AnotherDependentKey"])
{
// Handle another dependent key.
}
}
}
The reason for the comparison between the old and new values should be
obvious, namely, I don't want to redraw the screen unless the value of
the original key has in fact changed.
Now, here's the problem: when I run my app, both the old and new
values are logged as simply 0 (zero). That's clearly incorrect because
(a) not all of my properties are numbers (some are colors, for
example) and (b) I know I've made a change and yet the old and new
values come out equal.
Everything compiles fine, with no warnings of any kind, and the app
runs fine if I remove the comparison between old and new (but the old
and new values are still logged as zero).
Anyone has any idea of what I may be doing wrong?
Thanks in advance.
Wagner
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