Open Radar

 
Summary:
If you add an observer on a non-autonotifying object twice, call -willChangeValueForKey:, call -removeObserver:forKeyPath: once, change the value and then call -didChangeValueForKey:, the observer receives -observeValueForKeyPath:... messages twice instead of once.

Steps to Reproduce:
1. Compile and run the following code with Xcode 5.0.1, iOS 6.1 Simulator target

@interface Observer : NSObject
@end

@implementation Observer
{
    NSMutableDictionary *_observationCounts;
    NSMutableSet *_priorNotificationValues;
}

+ (instancetype)observer
{
    return [[[self alloc] init] autorelease];
}

- (id)init
{
    self = [super init];
    if (self != nil)
    {
        _observationCounts = [NSMutableDictionary dictionary];
        _priorNotificationValues = [NSMutableSet set];
    }
    return self;
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSNumber *count = [_observationCounts objectForKey:keyPath];
    if (count == nil)
    {
        count = @(0);
    }
    [_observationCounts setObject:@([count integerValue] + 1) forKey:keyPath];

    if ([change objectForKey:NSKeyValueChangeNotificationIsPriorKey] != nil)
    {
        [_priorNotificationValues addObject:keyPath];
    }
}

- (NSUInteger)observationCountForKeyPath:(NSString *)keyPath
{
    NSNumber *count = [_observationCounts objectForKey:keyPath];
    if (count == nil)
    {
        count = @(0);
    }

    return [count unsignedIntegerValue];
}

- (BOOL)priorObservationMadeForKeyPath:(NSString *)keyPath
{
    return [_priorNotificationValues containsObject:keyPath];
}

@end

@interface Observable : NSObject {
    int _anInt;
}
@property int anInt;
@property Class someClass;
@property union foo { int a; float b; } someUnion;
@end

@implementation Observable
@synthesize anInt=_anInt;
+ (instancetype)observable
{
    return [[[self alloc] init] autorelease];
}
@end
@interface ReallyBadObservable : Observable
@end

@implementation ReallyBadObservable
- (void)setAnInt:(int)anInt
{
    _anInt = anInt;
}
+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key
{
    return NO;
}
@end

-(BOOL)testMidCyclePartialUnregister
{
    @autoreleasepool
    {
        ReallyBadObservable *badObservable = [ReallyBadObservable observable];
        Observer *observer = [Observer observer];
        [badObservable addObserver:observer forKeyPath:@"anInt" options:0 context:NULL];
        [badObservable addObserver:observer forKeyPath:@"anInt" options:0 context:NULL];
        [badObservable willChangeValueForKey:@"anInt"];
        [badObservable setAnInt:50]; //this line and the following line can be rearranged without affecting the result.
        [badObservable removeObserver:observer forKeyPath:@"anInt"];
        [badObservable didChangeValueForKey:@"anInt"];
        testassert([observer observationCountForKeyPath:@"anInt"] == 1);
        [badObservable removeObserver:observer forKeyPath:@"anInt"];
        return YES;
    }
}


Expected Results:
This test should pass.

Actual Results:
This test fails. The call to [observer observationCountForKeyPath:@"anInt"] returns 2. 

Version:
6.1 Simulator