我有一个托管对象与成员类的一对多关系。当我为成员添加观察者时,它就起作用了。当一个新成员添加到关系中时,将使用新对象调用observeValueForKeyPath,并且更改字典包含新成员对象。然而,observeValueForKeyPath将被第二次触发,所有值为nil并且改变字典new =“NULL”。第二个触发器是什么?我设置了一个断点,但不知道谁是触发器。KVO为一对多,但NSNull对象传入observeValueForKeyPath
@interface FooObject : NSManagedObject {}
@property (nonatomic, strong) NSString *fooId;
@property (nonatomic, strong) NSSet* members;
@end
@implementation FooObject
@dynamic fooId;
@dynamic members;
- (NSMutableSet*)membersSet {
[self willAccessValueForKey:@"members"];
NSMutableSet *result = (NSMutableSet*)[self mutableSetValueForKey:@"members"];
[self didAccessValueForKey:@"members"];
return result;
}
- (void)registerObservers {
[self addObserver:self
forKeyPath:@"members"
options:NSKeyValueObservingOptionNew
context:nil];
}
- (void)unregisterObservers {
@try{
[self removeObserver:self forKeyPath:@"members"];
}@catch(id anException){
//do nothing, obviously it wasn't attached because an exception was thrown
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context
id valueNewSet = [change objectForKey:NSKeyValueChangeNewKey];
if (![valueNewSet isKindOfClass:[NSSet class]]) {
// not a NSSet, it contains <null> value
NSLog(@"%@", change);
NSLog(@"%@", object);
}
if ([[change objectForKey:NSKeyValueChangeKindKey] intValue] == NSKeyValueChangeInsertion) {
// insert change is valid, process the changes
}
}
@end
日志输出:
{
kind = 1;
new = "<null>";
}
<FooObject: 0xfa9cc60> (entity: FooObject; id: 0xfa9be00 <x-coredata://39DB31FD-6795-4FDE-B700-819AB22E5170/SHInterest/p6> ; data: {
fooId = nil;
members = nil;
})
EDIT 1 我在NSLog的设置断点(@ “%@”,变更); 这是堆栈跟踪,但对进行此调用的图形没有什么帮助。
主 - > UIApplicationMain - > NSKeyValueNotifyObserver - > observeValueForKeyPath:ofObject变化:上下文
EDIT 2 也许这仍然是一个错误? http://www.cocoabuilder.com/archive/cocoa/182567-kvo-observevalueforkeypath-not-reflecting-changes.html
当你停在断点处时,它应该会显示堆栈跟踪。这应该包含一些关于为什么被调用的线索。 – 2012-08-06 22:49:13
是的,但堆栈跟踪根本没有帮助。我更新了跟踪。 – angelokh 2012-08-06 23:21:08
这里的复杂因素是你并没有观察到一个单一的值,而是一个关系。从文档:“如果观察到的属性是一对多关系,则NSKeyValueChangeKindKey条目还会分别指示关系中的对象是插入,移除还是替换,分别返回NSKeyValueChangeInsertion,NSKeyValueChangeRemoval或NSKeyValueChangeReplacement。” – 2012-08-08 15:11:58