Question

当NSMutableDictionary的计数达到0时，我希望收到通知。如果没有扩展NSMutableDictionary（我听说你不应该这样做），这是可能的吗？

我可以吗有一个类别，通过调用原始的方法模拟删除方法，同时检查计数是否为0？或者是否有更简单的方法。我试过KVO，但那不起作用......

感谢任何帮助。

约瑟夫

Answer 1

我尝试了我的第一个类别，这似乎有效：

的NSMutableDictionary + NotifiesOnEmpty.h

#import <Foundation/Foundation.h>

@interface NSMutableDictionary (NotifiesOnEmpty)
- (void)removeObjectForKeyNotify:(id)aKey;
- (void)removeAllObjectsNotify;
- (void)removeObjectsForKeysNotify:(NSArray *)keyArray;
- (void)notifyOnEmpty;
@end

的NSMutableDictionary + NotifiesOnEmpty.m

#import "Constants.h"
#import "NSMutableDictionary+NotifiesOnEmpty.h"

@implementation NSMutableDictionary (NotifiesOnEmpty)
- (void)removeObjectForKeyNotify:(id)aKey {
    [self removeObjectForKey:aKey];
    [self notifyOnEmpty];
}

- (void)removeAllObjectsNotify {
    [self removeAllObjects];
    [self notifyOnEmpty];
}

- (void)removeObjectsForKeysNotify:(NSArray *)keyArray {
    [self removeObjectsForKeys:keyArray];
    [self notifyOnEmpty];
}

- (void)notifyOnEmpty {
    if ([self count] == 0) {
        [[NSNotificationCenter defaultCenter] postNotificationName:kNotificationDictionaryEmpty object:self];
    }
}
@end

不知道这是否是一个优雅的解决方案，但似乎工作正常。

Answer 2

使用字典和其他“类集群”对象时，“子类化”它们的最简单方法是创建一个子类并将其包装在相同类型的现有对象周围：

@interface MyNotifyingMutableDictionary:NSMutableDictionary {
    NSMutableDictionary *dict;
}

// these are the primitive methods you need to override
// they're the ones found in the NSDictionary and NSMutableDictionary
// class declarations themselves, rather than the categories in the .h.

- (NSUInteger)count;
- (id)objectForKey:(id)aKey;
- (NSEnumerator *)keyEnumerator;

- (void)removeObjectForKey:(id)aKey;
- (void)setObject:(id)anObject forKey:(id)aKey;

@end

@implementation MyNotifyingMutableDictionary 
- (id)init {
    if ((self = [super init])) {
        dict = [[NSMutableDictionary alloc] init];
    }
    return self;
}
- (NSUInteger)count {
    return [dict count];
}
- (id)objectForKey:(id)aKey {
    return [dict objectForKey:aKey];
}
- (NSEnumerator *)keyEnumerator {
    return [dict keyEnumerator];
}
- (void)removeObjectForKey:(id)aKey {
    [dict removeObjectForKey:aKey];
    [self notifyIfEmpty]; // you provide this method
}
- (void)setObject:(id)anObject forKey:(id)aKey {
    [dict setObject:anObject forKey:aKey];
}
- (void)dealloc {
    [dict release];
    [super dealloc];
}
@end

Objective-C：向NSMutableDictionary添加一个观察者，当计数达到0时，该观察者会收到通知

2 个答案: