有没有一种干净的方式来使用指针（ids）作为NSMutableDictionary中的键？

Question

我使用NSMutableDictionary来存储对某些类有效的描述符，因为我宁愿不浪费将描述符添加到类的每个实例的内存，因为只有1000个对象的非常小的子集才会有描述。

不幸的是，鉴于：

MyClass* p = [MyClass thingy]; 
NSMutableDictionary *dict = [NSMutableDictionary dictionary]; 
NSString* description = @"blah"; //does this work? If not I'm just simplifying for this example. 
[dict setObject:description forKey:p]; // BZZZZT a copy of p is made using NSCopying 

MyClass* found = [dict objectForKey:p]; //returns nil, as p becomes a different copy. 

所以这是行不通的。

我可以在一个NSNumber通过像这样破解它：

[dict setObject:description forKey:[NSNumber numberWithInt:(int)p]]; // this is cool 

但是，这不仅难看，而且容易出错，因为它是非标准的。

考虑到这一点，是否有一个干净的方法来做到这一点？

Answer 1

NSValue确认NSCopying按照NSValue Class Reference。所以你可以使用NSValue的一个实例作为关键。使用+valueWithPointer:将指针值向上包装。

NSString* foo = @"foo"; 
id bar = @"bar"; 

NSMutableDictionary* dict = [[NSMutableDictionary alloc] init]; 
[dict setObject:@"forKey:foo" forKey:foo]; 
[dict setObject:@"forKey:bar" forKey:bar]; 
[dict setObject:@"forKey:[NSValue... foo]" forKey:[NSValue valueWithPointer:foo]]; 
[dict setObject:@"forKey:[NSValue... bar]" forKey:[NSValue valueWithPointer:bar]]; 

NSLog(@"%@", [dict objectForKey:foo]); 
NSLog(@"%@", [dict objectForKey:bar]); 
NSLog(@"%@", [dict objectForKey:[NSValue valueWithPointer:foo]]); 
NSLog(@"%@", [dict objectForKey:[NSValue valueWithPointer:bar]]); 

给人

2013-01-24 04:42:14.051 a.out[67640:707] forKey:foo 
2013-01-24 04:42:14.052 a.out[67640:707] forKey:bar 
2013-01-24 04:42:14.053 a.out[67640:707] forKey:[NSValue... foo] 
2013-01-24 04:42:14.053 a.out[67640:707] forKey:[NSValue... bar] 

Answer 2

您的问题是，NSDictionary复制其密钥。要么让你的类实现NSCopying，要么使用一个CFMutableDictionary和一个不复制的密钥回调（它是toll-free bridged和NSMutableDictionary，所以你可以在它创建后使用它）。

Answer 3

您可能会发现它更易于使用objc_setAssociatedObject/objc_getAssociatedObject。他们被描述为here。

Answer 4

我个人的解决方案：

覆盖- (BOOL) isEqual:(id)object在你的自定义类。

在此方法中，比较self和object中的每个属性。如果它们相同，则返回YES

我不确定您是如何实施您的- (id) copyWithZone:(NSZone *)zone方法的，但对于我的测试项目而言，它可以正常工作。

附件：

- (id) copyWithZone:(NSZone *)zone{ 
    testObject *copy = [[testObject allocWithZone:zone] init]; 
    NSString *tempCopyString = [NSString stringWithString:self.string] 
    copy.string = tempCopyString; 
    return copy; 
} 

- (BOOL) isEqual:(id)object{ 
    testObject *newObject = (testObject*)object; 
    if ([newObject.string isEqualToString:object.string]) { 
     return YES; 
    } 
    else { 
     return NO; 
    } 
} 

Answer 5

由于这是经常发生的问题，我已经创建了下面的类对象到其他对象没有钥匙的复制关联。身份是在关键对象地址上确定的。 它是NSMutableDictionary的一个子类，因此该类的所有方法都可用。

ObjectMap.h

// 
// ObjectMap.h 
// 
// Created by René Dekker on 07/03/2012. 
// Copyright (c) 2012 Renevision. 
// 

#import <Foundation/Foundation.h> 

@interface ObjectMap : NSMutableDictionary 

+ (ObjectMap *) objectMap; 

- (bool) containsObject:(id)aKey; 

// use the following instead of setObject:forKey: in IOS 6, to avoid warnings about NSCopying 
- (void) setObject:(id)anObject forObjectKey:(id)aKey; 


@end 

ObjectMap.m

// 
// ObjectMap.m 
// 
// Created by René Dekker on 07/03/2012. 
// Copyright (c) 2012 Renevision. 
// 

#import "ObjectMap.h" 
#import <CoreFoundation/CoreFoundation.h> 

@interface ObjectMapEnumerator : NSEnumerator 

@end 

@implementation ObjectMapEnumerator { 
    NSUInteger size; 
    NSUInteger currentIndex; 
    id *keysArray; 
} 

- (NSArray *) allObjects 
{ 
    return [NSArray arrayWithObjects:keysArray count:size]; 
} 

- (id) nextObject 
{ 
    if (currentIndex >= size) { 
     return nil; 
    } 
    return keysArray[currentIndex++]; 
} 

- (id) initWithDict:(CFDictionaryRef)dict 
{ 
    if (!(self = [super init])) { 
     return nil; 
    } 
    size = CFDictionaryGetCount(dict); 
    keysArray = malloc(size * sizeof(id)); 
    currentIndex = 0; 
    CFDictionaryGetKeysAndValues(dict, (const void **)keysArray, NULL); 
    return self; 
} 

- (void) dealloc 
{ 
    free(keysArray); 
    [super dealloc]; 
} 

@end 

@implementation ObjectMap { 
    CFMutableDictionaryRef theDictionary; 
} 

- (void) setObject:(id)anObject forKey:(id)aKey 
{ 
    CFDictionarySetValue(theDictionary, aKey, anObject); 
} 

- (void) setObject:(id)anObject forObjectKey:(id)aKey 
{ 
    CFDictionarySetValue(theDictionary, aKey, anObject); 
} 

- (id) objectForKey:(id)aKey 
{ 
    return CFDictionaryGetValue(theDictionary, aKey); 
} 

- (void) removeObjectForKey:(id)aKey 
{ 
    CFDictionaryRemoveValue(theDictionary, aKey); 
} 

- (void) removeAllObjects 
{ 
    CFDictionaryRemoveAllValues(theDictionary); 
} 

- (bool) containsObject:(id)aKey 
{ 
    return CFDictionaryContainsKey(theDictionary, aKey); 
} 

- (NSUInteger) count 
{ 
    return CFDictionaryGetCount(theDictionary); 
} 

- (NSEnumerator *)keyEnumerator 
{ 
    return [[[ObjectMapEnumerator alloc] initWithDict:theDictionary] autorelease]; 
} 

#pragma - Object Life Cycle 

static void dictionaryRelease(CFAllocatorRef allocator, const void* value) { 
    if (0 != value) { 
     CFRelease(value); 
    } 
} 

static const void *dictionaryRetain(CFAllocatorRef allocator, const void* value) { 
    if (0 != value) { 
     return CFRetain(value); 
    } 
    return 0; 
} 

static CFDictionaryKeyCallBacks callbacks = { 0, &dictionaryRetain, &dictionaryRelease, &CFCopyDescription, NULL, NULL }; 

- (id) init 
{ 
    if (!(self = [super init])) { 
     return nil; 
    } 
    theDictionary = CFDictionaryCreateMutable(NULL, 0, &callbacks, &kCFTypeDictionaryValueCallBacks); 
    return self; 
} 

- (void) dealloc 
{ 
    CFRelease(theDictionary); 
    [super dealloc]; 
} 

+ (ObjectMap *) objectMap 
{ 
    return [[[ObjectMap alloc] init] autorelease]; 
} 

@end