On Apr 3, 2008, at 10:45AM, Jens Alfke wrote:
Properties and ivars are not the same thing. Properties are
shorthand for methods, not variables. A property doesn't have to
correspond to any instance variable, or to one with the identical
name.
Excellent point. I did not realize that.
Often when I feel short on knowledge and experience on a particular
topic I will look and see what Apple has done.
In reviewing CALayer.h again I noticed that this class has a ton of
properties (frame, bounds, position, zPosition, anchorPoint,
transform, sublayerTransform, contents, contentsRect, opaque,
contentsGravity, opacity, hidden, masksToBounds, etc.) but no
explicitly associated ivars that are visible.
The header looks like this.
@interface CALayer : NSObject <NSCoding, CAMediaTiming> {
@private
struct _CALayerIvars {
int32_t refcount;
uint32_t flags;
uintptr_t parent;
CFMutableArrayRef sublayers;
CALayer *mask;
struct _CALayerState *state;
struct _CALayerState *previous_state;
struct _CALayerAnimation *animations;
struct _CALayerTransaction *slots[3];
#if defined (__LP64__) && __LP64__
uint32_t reserved;
#endif
} _attr;
}
So perhaps any ivar which may be associated with a property are hidden
in "struct _CALayerState *state". If that is the case they why did
they hide some of the ivars but not all of them?
I have also been looking through the WebKit framework and noticed that
they will hide ALL of the instance variables in another class like this.
@interface WebView : NSView {
@private
WebViewPrivate *_private;
}
Can anyone shed light on this practice of hiding ivars? Is it mainly
something that is being done by the framework developers and generally
is not applicable to application developers? Why does Apple do this?
Regards,
Richard
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