我有一個託管對象與成員類的一對多關係。當我爲成員添加觀察者時,它就起作用了。當一個新成員添加到關係中時,將使用新對象調用observeValueForKeyPath,並且更改字典包含新成員對象。然而,observeValueForKeyPath將被第二次觸發,所有值爲nil並且改變字典new =「NULL」。第二個觸發器是什麼?我設置了一個斷點,但不知道誰是觸發器。KVO爲一對多,但NSNull對象傳入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
日誌輸出:
{
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的設置斷點(@ 「%@」,變更); 這是堆棧跟蹤,但對進行此調用的圖形沒有什麼幫助。
主 - > UIApplicationMain - > NSKeyValueNotifyObserver - > observeValueForKeyPath:ofObject變化:上下文
EDIT 2 也許這仍然是一個錯誤? http://www.cocoabuilder.com/archive/cocoa/182567-kvo-observevalueforkeypath-not-reflecting-changes.html
當你停在斷點處時,它應該會顯示堆棧跟蹤。這應該包含一些關於爲什麼被調用的線索。 – 2012-08-06 22:49:13
是的,但堆棧跟蹤根本沒有幫助。我更新了跟蹤。 – angelokh 2012-08-06 23:21:08
這裏的複雜因素是你並沒有觀察到一個單一的值,而是一個關係。從文檔:「如果觀察到的屬性是一對多關係,則NSKeyValueChangeKindKey條目還會分別指示關係中的對象是插入,移除還是替換,分別返回NSKeyValueChangeInsertion,NSKeyValueChangeRemoval或NSKeyValueChangeReplacement。」 – 2012-08-08 15:11:58