CALayer
has a special implementation for valueForKeyPath:
. For example, the following works:
CALayer *layer = [CALayer layer];
id x0 = [layer valueForKeyPath:@"bounds"];
// --> NSValue object containing a NSRect
id y0 = [layer valueForKeyPath:@"bounds.size"];
// --> NSValue object containing a NSSize
id z0 = [layer valueForKeyPath:@"bounds.size.width"];
// --> NSNumber object containing a float
But the following does not work:
CALayer *layer = [CALayer layer];
id x = [layer valueForKey:@"bounds"];
// --> NSValue object containing a NSRect
id y = [x valueForKey:@"size"];
// --> Exception: '[<NSConcreteValue 0x71189e0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key size.'
So generally, NSValue
objects containing a NSRect
or NSSize
are not key-value compliant. It works only with CALayer
because the valueForKeyPath:
implementation handles the entire key path, instead of evaluating the first key and passing down the remaining key path.
UIImage
does not have a special implementation for valueForKeyPath:
. Therefore
UIImage *img1 = [UIImage imageNamed:@"img1"];
id x1 = [img1 valueForKey:@"size"];
// --> NSValue containing a NSSize
works, but
UIImage *img1 = [UIImage imageNamed:@"img1"];
id x1 = [img1 valueForKeyPath:@"size.width"];
does not work.
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