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#import <Foundation/Foundation.h>
// SourceBase will be the base class of Source. We'll pass a Source object into a
// function as a SourceBase, and then see if the dynamic typing can get us through the KVO
// goo and all the way back to Source.
@interface SourceBase: NSObject
{
uint32_t _value;
}
- (SourceBase *) init;
- (uint32_t) getValue;
@end
@implementation SourceBase
- (SourceBase *) init
{
[super init];
_value = 10;
return self;
}
- (uint32_t) getValue
{
return _value;
}
@end
// Source is a class that will be observed by the Observer class below.
// When Observer sets itself up to observe this property (in initWithASource)
// the KVO system will overwrite the "isa" pointer of the object with the "kvo'ed"
// one.
@interface Source : SourceBase
{
int _property;
}
- (Source *) init;
- (void) setProperty: (int) newValue;
@end
@implementation Source
- (Source *) init
{
[super init];
_property = 20;
return self;
}
- (void) setProperty: (int) newValue
{
_property = newValue; // This is the line in setProperty, make sure we step to here.
}
@end
@interface SourceDerived : Source
{
int _derivedValue;
}
- (SourceDerived *) init;
- (uint32_t) getValue;
@end
@implementation SourceDerived
- (SourceDerived *) init
{
[super init];
_derivedValue = 30;
return self;
}
- (uint32_t) getValue
{
return _derivedValue;
}
@end
// Observer is the object that will watch Source and cause KVO to swizzle it...
@interface Observer : NSObject
{
Source *_source;
}
+ (Observer *) observerWithSource: (Source *) source;
- (Observer *) initWithASource: (Source *) source;
- (void) observeValueForKeyPath: (NSString *) path
ofObject: (id) object
change: (NSDictionary *) change
context: (void *) context;
@end
@implementation Observer
+ (Observer *) observerWithSource: (Source *) inSource;
{
Observer *retval;
retval = [[Observer alloc] initWithASource: inSource];
return retval;
}
- (Observer *) initWithASource: (Source *) source
{
[super init];
_source = source;
[_source addObserver: self
forKeyPath: @"property"
options: (NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
context: NULL];
return self;
}
- (void) observeValueForKeyPath: (NSString *) path
ofObject: (id) object
change: (NSDictionary *) change
context: (void *) context
{
printf ("Observer function called.\n");
return;
}
@end
uint32_t
handle_SourceBase (SourceBase *object)
{
return [object getValue]; // Break here to check dynamic values.
}
int main ()
{
Source *mySource;
Observer *myObserver;
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
mySource = [[SourceDerived alloc] init];
myObserver = [Observer observerWithSource: mySource];
[mySource setProperty: 5]; // Break here to see if we can step into real method.
uint32_t return_value = handle_SourceBase (mySource);
SourceDerived *unwatchedSource = [[SourceDerived alloc] init];
return_value = handle_SourceBase (unwatchedSource);
[pool release];
return 0;
}
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