Foundation/GTMNSObject+KeyValueObserving.m - external/google-toolbox-for-mac - Git at Google

 //
 //  GTMNSObject+KeyValueObserving.m
 //
 //  Copyright 2009 Google Inc.
 //
 //  Licensed under the Apache License, Version 2.0 (the "License"); you may not
 //  use this file except in compliance with the License.  You may obtain a copy
 //  of the License at
 //
 //  http://www.apache.org/licenses/LICENSE-2.0
 //
 //  Unless required by applicable law or agreed to in writing, software
 //  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 //  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 //  License for the specific language governing permissions and limitations under
 //  the License.
 //

 //
 //  MAKVONotificationCenter.m
 //  MAKVONotificationCenter
 //
 //  Created by Michael Ash on 10/15/08.
 //

 // This code is based on code by Michael Ash.
 // See comment in header.
 #import "GTMNSObject+KeyValueObserving.h"

 #import <libkern/OSAtomic.h>
 #include <objc/runtime.h>

 #import "GTMDefines.h"
 #import "GTMDebugSelectorValidation.h"
 #import "GTMMethodCheck.h"

 // A singleton that works as a dispatch center for KVO
 // -[NSObject observeValueForKeyPath:ofObject:change:context:] and turns them
 // into selector dispatches. It stores a collection of
 // GTMKeyValueObservingHelpers, and keys them via the key generated by
 // -dictionaryKeyForObserver:ofObject:forKeyPath:selector.
 @interface GTMKeyValueObservingCenter : NSObject {
  @private
   NSMutableDictionary *observerHelpers_;
 }

 + (id)defaultCenter;

 - (void)addObserver:(id)observer
            ofObject:(id)target
          forKeyPath:(NSString *)keyPath
            selector:(SEL)selector
            userInfo:(id)userInfo
             options:(NSKeyValueObservingOptions)options;
 - (void)removeObserver:(id)observer
               ofObject:(id)target
             forKeyPath:(NSString *)keyPath
               selector:(SEL)selector;
 - (id)dictionaryKeyForObserver:(id)observer
                       ofObject:(id)target
                     forKeyPath:(NSString *)keyPath
                       selector:(SEL)selector;
 @end

 @interface GTMKeyValueObservingHelper : NSObject {
  @private
   GTM_WEAK id observer_;
   SEL selector_;
   id userInfo_;
   GTM_WEAK id target_;
   NSString* keyPath_;
 }

 - (id)initWithObserver:(id)observer
                 object:(id)target
                keyPath:(NSString *)keyPath
               selector:(SEL)selector
               userInfo:(id)userInfo
                options:(NSKeyValueObservingOptions)options;
 - (void)deregister;

 @end

 @interface GTMKeyValueChangeNotification ()
 - (id)initWithKeyPath:(NSString *)keyPath ofObject:(id)object
              userInfo:(id)userInfo change:(NSDictionary *)change;
 @end

 @implementation GTMKeyValueObservingHelper

 // For info how and why we use these statics:
 // http://lists.apple.com/archives/cocoa-dev/2006/Jul/msg01038.html
 static char GTMKeyValueObservingHelperContextData;
 static char* GTMKeyValueObservingHelperContext
   = &GTMKeyValueObservingHelperContextData;

 - (id)initWithObserver:(id)observer
                 object:(id)target
                keyPath:(NSString *)keyPath
               selector:(SEL)selector
               userInfo:(id)userInfo
                options:(NSKeyValueObservingOptions)options {
   if((self = [super init])) {
     observer_ = observer;
     selector_ = selector;
     userInfo_ = [userInfo retain];

     target_ = target;
     keyPath_ = [keyPath retain];

     [target addObserver:self
              forKeyPath:keyPath
                 options:options
                 context:GTMKeyValueObservingHelperContext];
   }
   return self;
 }

 - (NSString *)description {
   return [NSString stringWithFormat:
           @"%@ <observer = %@ keypath = %@ target = %@ selector = %@>",
           [self class], observer_, keyPath_, target_,
           NSStringFromSelector(selector_)];
 }

 - (void)dealloc {
   if (target_) {
     _GTMDevLog(@"Didn't deregister %@", self);
     [self deregister];
   }
   [userInfo_ release];
   [keyPath_ release];
   [super dealloc];
 }

 - (void)observeValueForKeyPath:(NSString *)keyPath
                       ofObject:(id)object
                         change:(NSDictionary *)change
                        context:(void *)context {
   if(context == GTMKeyValueObservingHelperContext) {
     GTMKeyValueChangeNotification *notification
       = [[GTMKeyValueChangeNotification alloc] initWithKeyPath:keyPath
                                                       ofObject:object
                                                       userInfo:userInfo_
                                                         change:change];
     [observer_ performSelector:selector_ withObject:notification];
     [notification release];
   } else {
     // COV_NF_START
     // There's no way this should ever be called.
     // If it is, the call will go up to NSObject which will assert.
     [super observeValueForKeyPath:keyPath
                          ofObject:object
                            change:change
                           context:context];
     // COV_NF_END
   }
 }

 - (void)deregister {
   [target_ removeObserver:self forKeyPath:keyPath_];
   target_ = nil;
 }

 @end

 @implementation GTMKeyValueObservingCenter

 + (id)defaultCenter {
   static GTMKeyValueObservingCenter *center = nil;
   if(!center) {
     // do a bit of clever atomic setting to make this thread safe
     // if two threads try to set simultaneously, one will fail
     // and the other will set things up so that the failing thread
     // gets the shared center
     GTMKeyValueObservingCenter *newCenter = [[self alloc] init];
     if(!OSAtomicCompareAndSwapPtrBarrier(NULL,
                                          newCenter,
                                          (void *)&center)) {
       [newCenter release];  // COV_NF_LINE no guarantee we'll hit this line
     }
   }
   return center;
 }

 - (id)init {
   if((self = [super init])) {
     observerHelpers_ = [[NSMutableDictionary alloc] init];
   }
   return self;
 }

 // COV_NF_START
 // Singletons don't get deallocated
 - (void)dealloc {
   [observerHelpers_ release];
   [super dealloc];
 }
 // COV_NF_END

 - (id)dictionaryKeyForObserver:(id)observer
                       ofObject:(id)target
                     forKeyPath:(NSString *)keyPath
                       selector:(SEL)selector {
   NSString *key = nil;
   if (!target && !keyPath && !selector) {
     key = [NSString stringWithFormat:@"%p:", observer];
   } else {
     key = [NSString stringWithFormat:@"%p:%@:%p:%p",
            observer, keyPath, selector, target];
   }
   return key;
 }

 - (void)addObserver:(id)observer
            ofObject:(id)target
          forKeyPath:(NSString *)keyPath
            selector:(SEL)selector
            userInfo:(id)userInfo
             options:(NSKeyValueObservingOptions)options {
   GTMKeyValueObservingHelper *helper
     = [[GTMKeyValueObservingHelper alloc] initWithObserver:observer
                                                     object:target
                                                    keyPath:keyPath
                                                   selector:selector
                                                   userInfo:userInfo
                                                    options:options];
   id key = [self dictionaryKeyForObserver:observer
                                  ofObject:target
                                forKeyPath:keyPath
                                  selector:selector];
   @synchronized(self) {
     GTMKeyValueObservingHelper *oldHelper = [observerHelpers_ objectForKey:key];
     if (oldHelper) {
       _GTMDevLog(@"%@ already observing %@ forKeyPath %@",
                  observer, target, keyPath);
       [oldHelper deregister];
     }
     [observerHelpers_ setObject:helper forKey:key];
   }
   [helper release];
 }

 - (void)removeObserver:(id)observer
               ofObject:(id)target
             forKeyPath:(NSString *)keyPath
               selector:(SEL)selector {
   id key = [self dictionaryKeyForObserver:observer
                                  ofObject:target
                                forKeyPath:keyPath
                                  selector:selector];
   NSMutableArray *allValidHelperKeys = [NSMutableArray array];
   NSArray *allValidHelpers = nil;
   @synchronized(self) {

     NSString *helperKey;
     for (helperKey in [observerHelpers_ allKeys]) {
       if ([helperKey hasPrefix:key]) {
         [allValidHelperKeys addObject:helperKey];
       }
     }
 #if DEBUG
     if ([allValidHelperKeys count] == 0) {
       _GTMDevLog(@"%@ was not observing %@ with keypath %@",
                  observer, target, keyPath);
     }
 #endif // DEBUG
     allValidHelpers = [observerHelpers_ objectsForKeys:allValidHelperKeys
                                         notFoundMarker:[NSNull null]];
     [observerHelpers_ removeObjectsForKeys:allValidHelperKeys];
   }
   [allValidHelpers makeObjectsPerformSelector:@selector(deregister)];
 }

 @end

 @implementation NSObject (GTMKeyValueObservingAdditions)

 - (void)gtm_addObserver:(id)observer
              forKeyPath:(NSString *)keyPath
                selector:(SEL)selector
                userInfo:(id)userInfo
                 options:(NSKeyValueObservingOptions)options {
   _GTMDevAssert(observer && [keyPath length] && selector,
                 @"Missing observer, keyPath, or selector");
   GTMKeyValueObservingCenter *center
     = [GTMKeyValueObservingCenter defaultCenter];
   GTMAssertSelectorNilOrImplementedWithArguments(
       observer,
       selector,
       @encode(GTMKeyValueChangeNotification *),
       NULL);
   [center addObserver:observer
              ofObject:self
            forKeyPath:keyPath
              selector:selector
              userInfo:userInfo
               options:options];
 }

 - (void)gtm_removeObserver:(id)observer
                 forKeyPath:(NSString *)keyPath
                   selector:(SEL)selector {
   _GTMDevAssert(observer && [keyPath length] && selector,
                 @"Missing observer, keyPath, or selector");
   GTMKeyValueObservingCenter *center
     = [GTMKeyValueObservingCenter defaultCenter];
   GTMAssertSelectorNilOrImplementedWithArguments(
       observer,
       selector,
       @encode(GTMKeyValueChangeNotification *),
       NULL);
   [center removeObserver:observer
                 ofObject:self
               forKeyPath:keyPath
                 selector:selector];
 }

 - (void)gtm_stopObservingAllKeyPaths {
   GTMKeyValueObservingCenter *center
     = [GTMKeyValueObservingCenter defaultCenter];
   [center removeObserver:self
                 ofObject:nil
               forKeyPath:nil
                 selector:Nil];
 }

 @end


 @implementation GTMKeyValueChangeNotification

 - (id)initWithKeyPath:(NSString *)keyPath ofObject:(id)object
              userInfo:(id)userInfo change:(NSDictionary *)change {
   if ((self = [super init])) {
     keyPath_ = [keyPath copy];
     object_ = [object retain];
     userInfo_ = [userInfo retain];
     change_ = [change retain];
   }
   return self;
 }

 - (void)dealloc {
   [keyPath_ release];
   [object_ release];
   [userInfo_ release];
   [change_ release];
   [super dealloc];
 }

 - (id)copyWithZone:(NSZone *)zone {
   return [[[self class] allocWithZone:zone] initWithKeyPath:keyPath_
                                                    ofObject:object_
                                                    userInfo:userInfo_
                                                      change:change_];
 }

 - (BOOL)isEqual:(id)object {
   return ([keyPath_ isEqualToString:[object keyPath]]
           && [object_ isEqual:[object object]]
           && [userInfo_ isEqual:[object userInfo]]
           && [change_ isEqual:[object change]]);
 }

 - (NSString *)description {
   return [NSString stringWithFormat:
           @"%@ <object = %@ keypath = %@ userInfo = %@ change = %@>",
           [self class], object_, keyPath_, userInfo_, change_];
 }

 - (NSUInteger)hash {
   return [keyPath_ hash] + [object_ hash] + [userInfo_ hash] + [change_ hash];
 }

 - (NSString *)keyPath {
   return keyPath_;
 }

 - (id)object {
   return object_;
 }

 - (id)userInfo {
   return userInfo_;
 }

 - (NSDictionary *)change {
   return change_;
 }

 @end

 #ifdef DEBUG

 static void SwizzleMethodsInClass(Class cls, SEL sel1, SEL sel2) {
   Method m1 = class_getInstanceMethod(cls, sel1);
   Method m2 = class_getInstanceMethod(cls, sel2);
   method_exchangeImplementations(m1, m2);
 }

 // This category exists to attempt to help deal with tricky KVO issues.
 // KVO is a wonderful technology in some ways, but is extremely fragile and
 // allows developers a lot of freedom to shoot themselves in the foot.
 // Refactoring an app that uses a lot of KVO can be really difficult, as can
 // debugging it.
 // These are some tools that we have found useful when working with KVO. Note
 // that these tools are only on in Debug builds.
 // To enable our KVO debugging, set the GTMDebugKVO environment
 // variable to 1 and you will get a whole pile of KVO logging that may help you
 // track down problems.
 // bash - export GTMDebugKVO=1
 // csh/tcsh - setenv GTMDebugKVO 1
 //

 @interface NSObject (GTMDebugKeyValueObserving)
 - (void)_gtmDebugAddObserver:(NSObject *)observer
                   forKeyPath:(NSString *)keyPath
                      options:(NSKeyValueObservingOptions)options
                      context:(void *)context;
 - (void)_gtmDebugArrayAddObserver:(NSObject *)observer
                toObjectsAtIndexes:(NSIndexSet *)indexes
                        forKeyPath:(NSString *)keyPath
                           options:(NSKeyValueObservingOptions)options
                           context:(void *)context;
 - (void)_gtmDebugRemoveObserver:(NSObject *)observer
                      forKeyPath:(NSString *)keyPath;
 - (void)_gtmDebugArrayRemoveObserver:(NSObject *)observer
                 fromObjectsAtIndexes:(NSIndexSet *)indexes
                           forKeyPath:(NSString *)keyPath;
 - (void)_gtmDebugWillChangeValueForKey:(NSString*)key;
 - (void)_gtmDebugDidChangeValueForKey:(NSString*)key;

 @end

 @implementation NSObject (GTMDebugKeyValueObserving)
 GTM_METHOD_CHECK(NSObject, _gtmDebugAddObserver:forKeyPath:options:context:);
 GTM_METHOD_CHECK(NSObject, _gtmDebugRemoveObserver:forKeyPath:);
 GTM_METHOD_CHECK(NSObject, _gtmDebugWillChangeValueForKey:);
 GTM_METHOD_CHECK(NSObject, _gtmDebugDidChangeValueForKey:);
 GTM_METHOD_CHECK(NSArray,
     _gtmDebugArrayAddObserver:toObjectsAtIndexes:forKeyPath:options:context:);
 GTM_METHOD_CHECK(NSArray,
     _gtmDebugArrayRemoveObserver:fromObjectsAtIndexes:forKeyPath:);

 + (void)load {
   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
   NSDictionary *env = [[NSProcessInfo processInfo] environment];
   id debugKeyValue = [env valueForKey:@"GTMDebugKVO"];
   BOOL debug = NO;
   if ([debugKeyValue isKindOfClass:[NSNumber class]]) {
     debug = [debugKeyValue intValue] != 0 ? YES : NO;
   } else if ([debugKeyValue isKindOfClass:[NSString class]]) {
     debug = ([debugKeyValue hasPrefix:@"Y"] || [debugKeyValue hasPrefix:@"T"] ||
              [debugKeyValue intValue]);
   }
   Class cls = Nil;
   if (debug) {
     cls = [NSObject class];
     SwizzleMethodsInClass(cls,
         @selector(addObserver:forKeyPath:options:context:),
         @selector(_gtmDebugAddObserver:forKeyPath:options:context:));
     SwizzleMethodsInClass(cls,
         @selector(removeObserver:forKeyPath:),
         @selector(_gtmDebugRemoveObserver:forKeyPath:));
     SwizzleMethodsInClass(cls,
         @selector(willChangeValueForKey:),
         @selector(_gtmDebugWillChangeValueForKey:));
     SwizzleMethodsInClass(cls,
         @selector(didChangeValueForKey:),
         @selector(_gtmDebugDidChangeValueForKey:));
     cls = [NSArray class];
     SwizzleMethodsInClass(cls,
         @selector(addObserver:toObjectsAtIndexes:forKeyPath:options:context:),
         @selector(_gtmDebugArrayAddObserver:toObjectsAtIndexes:forKeyPath:options:context:));
     SwizzleMethodsInClass(cls,
         @selector(removeObserver:fromObjectsAtIndexes:forKeyPath:),
         @selector(_gtmDebugArrayRemoveObserver:fromObjectsAtIndexes:forKeyPath:));
   }
   [pool drain];
 }

 - (void)_gtmDebugAddObserver:(NSObject *)observer
                   forKeyPath:(NSString *)keyPath
                      options:(NSKeyValueObservingOptions)options
                      context:(void *)context {
   _GTMDevLog(@"Adding observer %@ to %@ keypath '%@'", observer, self, keyPath);
   [self _gtmDebugAddObserver:observer forKeyPath:keyPath
                      options:options context:context];
 }

 - (void)_gtmDebugArrayAddObserver:(NSObject *)observer
                toObjectsAtIndexes:(NSIndexSet *)indexes
                        forKeyPath:(NSString *)keyPath
                           options:(NSKeyValueObservingOptions)options
                           context:(void *)context {
   _GTMDevLog(@"Array adding observer %@ to indexes %@ of %@ keypath '%@'",
              observer, indexes, self, keyPath);
   [self _gtmDebugArrayAddObserver:observer
                toObjectsAtIndexes:indexes
                        forKeyPath:keyPath
                           options:options context:context];
 }

 - (void)_gtmDebugRemoveObserver:(NSObject *)observer
                      forKeyPath:(NSString *)keyPath {
   _GTMDevLog(@"Removing observer %@ from %@ keypath '%@'",
              observer, self, keyPath);
   [self _gtmDebugRemoveObserver:observer forKeyPath:keyPath];
 }

 - (void)_gtmDebugArrayRemoveObserver:(NSObject *)observer
                 fromObjectsAtIndexes:(NSIndexSet *)indexes
                           forKeyPath:(NSString *)keyPath {
   _GTMDevLog(@"Array removing observer %@ from indexes %@ of %@ keypath '%@'",
              indexes, observer, self, keyPath);
   [self _gtmDebugArrayRemoveObserver:observer
                 fromObjectsAtIndexes:indexes
                           forKeyPath:keyPath];
 }

 - (void)_gtmDebugWillChangeValueForKey:(NSString*)key {
   _GTMDevLog(@"Will change '%@' of %@", key, self);
   [self _gtmDebugWillChangeValueForKey:key];
 }

 - (void)_gtmDebugDidChangeValueForKey:(NSString*)key {
   _GTMDevLog(@"Did change '%@' of %@", key, self);
   [self _gtmDebugDidChangeValueForKey:key];
 }

 @end

 #endif  // DEBUG
	//
	// GTMNSObject+KeyValueObserving.m
	//
	// Copyright 2009 Google Inc.
	//
	// Licensed under the Apache License, Version 2.0 (the "License"); you may not
	// use this file except in compliance with the License. You may obtain a copy
	// of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
	// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
	// License for the specific language governing permissions and limitations under
	// the License.
	//

	//
	// MAKVONotificationCenter.m
	// MAKVONotificationCenter
	//
	// Created by Michael Ash on 10/15/08.
	//

	// This code is based on code by Michael Ash.
	// See comment in header.
	#import "GTMNSObject+KeyValueObserving.h"

	#import <libkern/OSAtomic.h>
	#include <objc/runtime.h>

	#import "GTMDefines.h"
	#import "GTMDebugSelectorValidation.h"
	#import "GTMMethodCheck.h"

	// A singleton that works as a dispatch center for KVO
	// -[NSObject observeValueForKeyPath:ofObject:change:context:] and turns them
	// into selector dispatches. It stores a collection of
	// GTMKeyValueObservingHelpers, and keys them via the key generated by
	// -dictionaryKeyForObserver:ofObject:forKeyPath:selector.
	@interface GTMKeyValueObservingCenter : NSObject {
	@private
	NSMutableDictionary *observerHelpers_;
	}

	+ (id)defaultCenter;

	- (void)addObserver:(id)observer
	ofObject:(id)target
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector
	userInfo:(id)userInfo
	options:(NSKeyValueObservingOptions)options;
	- (void)removeObserver:(id)observer
	ofObject:(id)target
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector;
	- (id)dictionaryKeyForObserver:(id)observer
	ofObject:(id)target
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector;
	@end

	@interface GTMKeyValueObservingHelper : NSObject {
	@private
	GTM_WEAK id observer_;
	SEL selector_;
	id userInfo_;
	GTM_WEAK id target_;
	NSString* keyPath_;
	}

	- (id)initWithObserver:(id)observer
	object:(id)target
	keyPath:(NSString *)keyPath
	selector:(SEL)selector
	userInfo:(id)userInfo
	options:(NSKeyValueObservingOptions)options;
	- (void)deregister;

	@end

	@interface GTMKeyValueChangeNotification ()
	- (id)initWithKeyPath:(NSString *)keyPath ofObject:(id)object
	userInfo:(id)userInfo change:(NSDictionary *)change;
	@end

	@implementation GTMKeyValueObservingHelper

	// For info how and why we use these statics:
	// http://lists.apple.com/archives/cocoa-dev/2006/Jul/msg01038.html
	static char GTMKeyValueObservingHelperContextData;
	static char* GTMKeyValueObservingHelperContext
	= &GTMKeyValueObservingHelperContextData;

	- (id)initWithObserver:(id)observer
	object:(id)target
	keyPath:(NSString *)keyPath
	selector:(SEL)selector
	userInfo:(id)userInfo
	options:(NSKeyValueObservingOptions)options {
	if((self = [super init])) {
	observer_ = observer;
	selector_ = selector;
	userInfo_ = [userInfo retain];

	target_ = target;
	keyPath_ = [keyPath retain];

	[target addObserver:self
	forKeyPath:keyPath
	options:options
	context:GTMKeyValueObservingHelperContext];
	}
	return self;
	}

	- (NSString *)description {
	return [NSString stringWithFormat:
	@"%@ <observer = %@ keypath = %@ target = %@ selector = %@>",
	[self class], observer_, keyPath_, target_,
	NSStringFromSelector(selector_)];
	}

	- (void)dealloc {
	if (target_) {
	_GTMDevLog(@"Didn't deregister %@", self);
	[self deregister];
	}
	[userInfo_ release];
	[keyPath_ release];
	[super dealloc];
	}

	- (void)observeValueForKeyPath:(NSString *)keyPath
	ofObject:(id)object
	change:(NSDictionary *)change
	context:(void *)context {
	if(context == GTMKeyValueObservingHelperContext) {
	GTMKeyValueChangeNotification *notification
	= [[GTMKeyValueChangeNotification alloc] initWithKeyPath:keyPath
	ofObject:object
	userInfo:userInfo_
	change:change];
	[observer_ performSelector:selector_ withObject:notification];
	[notification release];
	} else {
	// COV_NF_START
	// There's no way this should ever be called.
	// If it is, the call will go up to NSObject which will assert.
	[super observeValueForKeyPath:keyPath
	ofObject:object
	change:change
	context:context];
	// COV_NF_END
	}
	}

	- (void)deregister {
	[target_ removeObserver:self forKeyPath:keyPath_];
	target_ = nil;
	}

	@end

	@implementation GTMKeyValueObservingCenter

	+ (id)defaultCenter {
	static GTMKeyValueObservingCenter *center = nil;
	if(!center) {
	// do a bit of clever atomic setting to make this thread safe
	// if two threads try to set simultaneously, one will fail
	// and the other will set things up so that the failing thread
	// gets the shared center
	GTMKeyValueObservingCenter *newCenter = [[self alloc] init];
	if(!OSAtomicCompareAndSwapPtrBarrier(NULL,
	newCenter,
	(void *)&center)) {
	[newCenter release]; // COV_NF_LINE no guarantee we'll hit this line
	}
	}
	return center;
	}

	- (id)init {
	if((self = [super init])) {
	observerHelpers_ = [[NSMutableDictionary alloc] init];
	}
	return self;
	}

	// COV_NF_START
	// Singletons don't get deallocated
	- (void)dealloc {
	[observerHelpers_ release];
	[super dealloc];
	}
	// COV_NF_END

	- (id)dictionaryKeyForObserver:(id)observer
	ofObject:(id)target
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector {
	NSString *key = nil;
	if (!target && !keyPath && !selector) {
	key = [NSString stringWithFormat:@"%p:", observer];
	} else {
	key = [NSString stringWithFormat:@"%p:%@:%p:%p",
	observer, keyPath, selector, target];
	}
	return key;
	}

	- (void)addObserver:(id)observer
	ofObject:(id)target
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector
	userInfo:(id)userInfo
	options:(NSKeyValueObservingOptions)options {
	GTMKeyValueObservingHelper *helper
	= [[GTMKeyValueObservingHelper alloc] initWithObserver:observer
	object:target
	keyPath:keyPath
	selector:selector
	userInfo:userInfo
	options:options];
	id key = [self dictionaryKeyForObserver:observer
	ofObject:target
	forKeyPath:keyPath
	selector:selector];
	@synchronized(self) {
	GTMKeyValueObservingHelper *oldHelper = [observerHelpers_ objectForKey:key];
	if (oldHelper) {
	_GTMDevLog(@"%@ already observing %@ forKeyPath %@",
	observer, target, keyPath);
	[oldHelper deregister];
	}
	[observerHelpers_ setObject:helper forKey:key];
	}
	[helper release];
	}

	- (void)removeObserver:(id)observer
	ofObject:(id)target
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector {
	id key = [self dictionaryKeyForObserver:observer
	ofObject:target
	forKeyPath:keyPath
	selector:selector];
	NSMutableArray *allValidHelperKeys = [NSMutableArray array];
	NSArray *allValidHelpers = nil;
	@synchronized(self) {

	NSString *helperKey;
	for (helperKey in [observerHelpers_ allKeys]) {
	if ([helperKey hasPrefix:key]) {
	[allValidHelperKeys addObject:helperKey];
	}
	}
	#if DEBUG
	if ([allValidHelperKeys count] == 0) {
	_GTMDevLog(@"%@ was not observing %@ with keypath %@",
	observer, target, keyPath);
	}
	#endif // DEBUG
	allValidHelpers = [observerHelpers_ objectsForKeys:allValidHelperKeys
	notFoundMarker:[NSNull null]];
	[observerHelpers_ removeObjectsForKeys:allValidHelperKeys];
	}
	[allValidHelpers makeObjectsPerformSelector:@selector(deregister)];
	}

	@end

	@implementation NSObject (GTMKeyValueObservingAdditions)

	- (void)gtm_addObserver:(id)observer
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector
	userInfo:(id)userInfo
	options:(NSKeyValueObservingOptions)options {
	_GTMDevAssert(observer && [keyPath length] && selector,
	@"Missing observer, keyPath, or selector");
	GTMKeyValueObservingCenter *center
	= [GTMKeyValueObservingCenter defaultCenter];
	GTMAssertSelectorNilOrImplementedWithArguments(
	observer,
	selector,
	@encode(GTMKeyValueChangeNotification *),
	NULL);
	[center addObserver:observer
	ofObject:self
	forKeyPath:keyPath
	selector:selector
	userInfo:userInfo
	options:options];
	}

	- (void)gtm_removeObserver:(id)observer
	forKeyPath:(NSString *)keyPath
	selector:(SEL)selector {
	_GTMDevAssert(observer && [keyPath length] && selector,
	@"Missing observer, keyPath, or selector");
	GTMKeyValueObservingCenter *center
	= [GTMKeyValueObservingCenter defaultCenter];
	GTMAssertSelectorNilOrImplementedWithArguments(
	observer,
	selector,
	@encode(GTMKeyValueChangeNotification *),
	NULL);
	[center removeObserver:observer
	ofObject:self
	forKeyPath:keyPath
	selector:selector];
	}

	- (void)gtm_stopObservingAllKeyPaths {
	GTMKeyValueObservingCenter *center
	= [GTMKeyValueObservingCenter defaultCenter];
	[center removeObserver:self
	ofObject:nil
	forKeyPath:nil
	selector:Nil];
	}

	@end


	@implementation GTMKeyValueChangeNotification

	- (id)initWithKeyPath:(NSString *)keyPath ofObject:(id)object
	userInfo:(id)userInfo change:(NSDictionary *)change {
	if ((self = [super init])) {
	keyPath_ = [keyPath copy];
	object_ = [object retain];
	userInfo_ = [userInfo retain];
	change_ = [change retain];
	}
	return self;
	}

	- (void)dealloc {
	[keyPath_ release];
	[object_ release];
	[userInfo_ release];
	[change_ release];
	[super dealloc];
	}

	- (id)copyWithZone:(NSZone *)zone {
	return [[[self class] allocWithZone:zone] initWithKeyPath:keyPath_
	ofObject:object_
	userInfo:userInfo_
	change:change_];
	}

	- (BOOL)isEqual:(id)object {
	return ([keyPath_ isEqualToString:[object keyPath]]
	&& [object_ isEqual:[object object]]
	&& [userInfo_ isEqual:[object userInfo]]
	&& [change_ isEqual:[object change]]);
	}

	- (NSString *)description {
	return [NSString stringWithFormat:
	@"%@ <object = %@ keypath = %@ userInfo = %@ change = %@>",
	[self class], object_, keyPath_, userInfo_, change_];
	}

	- (NSUInteger)hash {
	return [keyPath_ hash] + [object_ hash] + [userInfo_ hash] + [change_ hash];
	}

	- (NSString *)keyPath {
	return keyPath_;
	}

	- (id)object {
	return object_;
	}

	- (id)userInfo {
	return userInfo_;
	}

	- (NSDictionary *)change {
	return change_;
	}

	@end

	#ifdef DEBUG

	static void SwizzleMethodsInClass(Class cls, SEL sel1, SEL sel2) {
	Method m1 = class_getInstanceMethod(cls, sel1);
	Method m2 = class_getInstanceMethod(cls, sel2);
	method_exchangeImplementations(m1, m2);
	}

	// This category exists to attempt to help deal with tricky KVO issues.
	// KVO is a wonderful technology in some ways, but is extremely fragile and
	// allows developers a lot of freedom to shoot themselves in the foot.
	// Refactoring an app that uses a lot of KVO can be really difficult, as can
	// debugging it.
	// These are some tools that we have found useful when working with KVO. Note
	// that these tools are only on in Debug builds.
	// To enable our KVO debugging, set the GTMDebugKVO environment
	// variable to 1 and you will get a whole pile of KVO logging that may help you
	// track down problems.
	// bash - export GTMDebugKVO=1
	// csh/tcsh - setenv GTMDebugKVO 1
	//

	@interface NSObject (GTMDebugKeyValueObserving)
	- (void)_gtmDebugAddObserver:(NSObject *)observer
	forKeyPath:(NSString *)keyPath
	options:(NSKeyValueObservingOptions)options
	context:(void *)context;
	- (void)_gtmDebugArrayAddObserver:(NSObject *)observer
	toObjectsAtIndexes:(NSIndexSet *)indexes
	forKeyPath:(NSString *)keyPath
	options:(NSKeyValueObservingOptions)options
	context:(void *)context;
	- (void)_gtmDebugRemoveObserver:(NSObject *)observer
	forKeyPath:(NSString *)keyPath;
	- (void)_gtmDebugArrayRemoveObserver:(NSObject *)observer
	fromObjectsAtIndexes:(NSIndexSet *)indexes
	forKeyPath:(NSString *)keyPath;
	- (void)_gtmDebugWillChangeValueForKey:(NSString*)key;
	- (void)_gtmDebugDidChangeValueForKey:(NSString*)key;

	@end

	@implementation NSObject (GTMDebugKeyValueObserving)
	GTM_METHOD_CHECK(NSObject, _gtmDebugAddObserver:forKeyPath:options:context:);
	GTM_METHOD_CHECK(NSObject, _gtmDebugRemoveObserver:forKeyPath:);
	GTM_METHOD_CHECK(NSObject, _gtmDebugWillChangeValueForKey:);
	GTM_METHOD_CHECK(NSObject, _gtmDebugDidChangeValueForKey:);
	GTM_METHOD_CHECK(NSArray,
	_gtmDebugArrayAddObserver:toObjectsAtIndexes:forKeyPath:options:context:);
	GTM_METHOD_CHECK(NSArray,
	_gtmDebugArrayRemoveObserver:fromObjectsAtIndexes:forKeyPath:);

	+ (void)load {
	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	NSDictionary *env = [[NSProcessInfo processInfo] environment];
	id debugKeyValue = [env valueForKey:@"GTMDebugKVO"];
	BOOL debug = NO;
	if ([debugKeyValue isKindOfClass:[NSNumber class]]) {
	debug = [debugKeyValue intValue] != 0 ? YES : NO;
	} else if ([debugKeyValue isKindOfClass:[NSString class]]) {
	debug = ([debugKeyValue hasPrefix:@"Y"] \|\| [debugKeyValue hasPrefix:@"T"] \|\|
	[debugKeyValue intValue]);
	}
	Class cls = Nil;
	if (debug) {
	cls = [NSObject class];
	SwizzleMethodsInClass(cls,
	@selector(addObserver:forKeyPath:options:context:),
	@selector(_gtmDebugAddObserver:forKeyPath:options:context:));
	SwizzleMethodsInClass(cls,
	@selector(removeObserver:forKeyPath:),
	@selector(_gtmDebugRemoveObserver:forKeyPath:));
	SwizzleMethodsInClass(cls,
	@selector(willChangeValueForKey:),
	@selector(_gtmDebugWillChangeValueForKey:));
	SwizzleMethodsInClass(cls,
	@selector(didChangeValueForKey:),
	@selector(_gtmDebugDidChangeValueForKey:));
	cls = [NSArray class];
	SwizzleMethodsInClass(cls,
	@selector(addObserver:toObjectsAtIndexes:forKeyPath:options:context:),
	@selector(_gtmDebugArrayAddObserver:toObjectsAtIndexes:forKeyPath:options:context:));
	SwizzleMethodsInClass(cls,
	@selector(removeObserver:fromObjectsAtIndexes:forKeyPath:),
	@selector(_gtmDebugArrayRemoveObserver:fromObjectsAtIndexes:forKeyPath:));
	}
	[pool drain];
	}

	- (void)_gtmDebugAddObserver:(NSObject *)observer
	forKeyPath:(NSString *)keyPath
	options:(NSKeyValueObservingOptions)options
	context:(void *)context {
	_GTMDevLog(@"Adding observer %@ to %@ keypath '%@'", observer, self, keyPath);
	[self _gtmDebugAddObserver:observer forKeyPath:keyPath
	options:options context:context];
	}

	- (void)_gtmDebugArrayAddObserver:(NSObject *)observer
	toObjectsAtIndexes:(NSIndexSet *)indexes
	forKeyPath:(NSString *)keyPath
	options:(NSKeyValueObservingOptions)options
	context:(void *)context {
	_GTMDevLog(@"Array adding observer %@ to indexes %@ of %@ keypath '%@'",
	observer, indexes, self, keyPath);
	[self _gtmDebugArrayAddObserver:observer
	toObjectsAtIndexes:indexes
	forKeyPath:keyPath
	options:options context:context];
	}

	- (void)_gtmDebugRemoveObserver:(NSObject *)observer
	forKeyPath:(NSString *)keyPath {
	_GTMDevLog(@"Removing observer %@ from %@ keypath '%@'",
	observer, self, keyPath);
	[self _gtmDebugRemoveObserver:observer forKeyPath:keyPath];
	}

	- (void)_gtmDebugArrayRemoveObserver:(NSObject *)observer
	fromObjectsAtIndexes:(NSIndexSet *)indexes
	forKeyPath:(NSString *)keyPath {
	_GTMDevLog(@"Array removing observer %@ from indexes %@ of %@ keypath '%@'",
	indexes, observer, self, keyPath);
	[self _gtmDebugArrayRemoveObserver:observer
	fromObjectsAtIndexes:indexes
	forKeyPath:keyPath];
	}

	- (void)_gtmDebugWillChangeValueForKey:(NSString*)key {
	_GTMDevLog(@"Will change '%@' of %@", key, self);
	[self _gtmDebugWillChangeValueForKey:key];
	}

	- (void)_gtmDebugDidChangeValueForKey:(NSString*)key {
	_GTMDevLog(@"Did change '%@' of %@", key, self);
	[self _gtmDebugDidChangeValueForKey:key];
	}

	@end

	#endif // DEBUG