一個項(xiàng)目中的需求

在iOS項(xiàng)目開發(fā)過程中，我們經(jīng)常會使用到NSSet凄贩、NSArray、NSDictionary三個類袱讹，它們?yōu)槲覀冊O(shè)計(jì)較友好的數(shù)據(jù)結(jié)構(gòu)時提供了很方便的方法

先準(zhǔn)備本文中將要使用的對象:

#import <Foundation/Foundation.h>

@interface HHHuman : NSObject

@property (nonatomic ,strong) NSString *name;

+ (instancetype) humanWithName:(NSString *)n;

@end

@implementation HHHuman

+ (instancetype) humanWithName:(NSString *)n
{
    HHHuman *human = [[HHHuman alloc] init];
    human.name = n;
    
    return [human autorelease];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@'s retainCount is %lu",self.name,[self retainCount]];
}
- (void)dealloc
{
    self.name = nil;
    [super dealloc];
}
@end

在程序開發(fā)過程中,經(jīng)常會用到諸如此類的Model對象.
用法呢也大致會有如下幾種方式:
1.通過有序的數(shù)列進(jìn)行存儲,數(shù)組NSArray;

    HHHuman *human_1 = [HHHuman humanWithName:@"lilei"];
    HHHuman *human_2 = [HHHuman humanWithName:@"hanmeimei"];
    HHHuman *human_3 = [HHHuman humanWithName:@"lewis"];
    HHHuman *human_4 = [HHHuman humanWithName:@"xiaohao"];
    HHHuman *human_5 = [HHHuman humanWithName:@"beijing"];

    id list = @[human_1,human_2,human_3,human_4,human_5];
    NSLog(@"%@",list);

輸出的結(jié)果如下:

(
    "lilei's retainCount is 2",
    "hanmeimei's retainCount is 2",
    "lewis's retainCount is 2",
    "xiaohao's retainCount is 2",
    "beijing's retainCount is 2"
)

2.通過統(tǒng)一的關(guān)鍵字進(jìn)行存儲,字典NSDictionary;

    HHHuman *human_1 = [HHHuman humanWithName:@"lilei"];
    HHHuman *human_2 = [HHHuman humanWithName:@"hanmeimei"];
    HHHuman *human_3 = [HHHuman humanWithName:@"lewis"];
    HHHuman *human_4 = [HHHuman humanWithName:@"xiaohao"];
    HHHuman *human_5 = [HHHuman humanWithName:@"beijing"];
    id dic = @{@"excellent":human_1};
    //同樣在控制臺輸出上文字典疲扎，用來查看每個對象的保留值
    NSLog(@"%@",list);

輸出的結(jié)果如下:

(
    "lilei's retainCount is 3",
    "hanmeimei's retainCount is 3",
    "lewis's retainCount is 2",
    "xiaohao's retainCount is 2",
    "beijing's retainCount is 2"
)

通過上述兩個例子我們能夠發(fā)現(xiàn)一個問題，即將對象添加到容器時捷雕，會對該對象的引用技術(shù)+1
這樣就會有可能發(fā)生循環(huán)持有的問題椒丧，例如如下代碼:

@interface HHHuman : NSObject

@property (nonatomic ,strong) NSString *name;
@property (nonatomic ,strong) NSMutableArray *family;

+ (instancetype) humanWithName:(NSString *)n;

@end

@implementation HHHuman

+ (instancetype) humanWithName:(NSString *)n
{
    HHHuman *human = [[HHHuman alloc] init];
    human.name = n;
    human.family = [[NSMutableArray alloc] init];
    [human.family addObject:human];

    return [human autorelease];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@'s retainCount is %lu",self.name,[self retainCount]];
}
- (void)dealloc
{
    self.name = nil;
    self.family = nil;
    [super dealloc];
}

@end

在以上代碼中,一個human的實(shí)例對象中包含一個strong修飾的family屬性，但是在family屬性中救巷，又添加了human自身對象壶熏，這樣會造成循環(huán)持有的問題，而導(dǎo)致內(nèi)存泄漏浦译。
但是項(xiàng)目需求又要求我們在該Model對象中完成如此代碼棒假，我們不得已會多創(chuàng)建一個類HHHumanRelationShip,如下所示:

#import <Foundation/Foundation.h>



@interface HHHuman : NSObject

@property (nonatomic ,strong) NSString *name;

+ (instancetype) humanWithName:(NSString *)n;

@end

@implementation HHHuman

+ (instancetype) humanWithName:(NSString *)n
{
    HHHuman *human = [[HHHuman alloc] init];
    human.name = n;

    return [human autorelease];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@'s retainCount is %lu",self.name,[self retainCount]];
}
- (void)dealloc
{
    self.name = nil;
    [super dealloc];
}

@end

@interface HHHumanRelationShip : NSObject

@property (nonatomic ,strong) HHHuman *human;
@property (nonatomic ,strong) NSArray *family;

+ (instancetype)relationShipWithHuman:(HHHuman *)human family:(NSArray *)members;

@end

@implementation HHHumanRelationShip

+ (instancetype)relationShipWithHuman:(HHHuman *)human family:(NSArray *)members
{
    HHHumanRelationShip *rs = [[HHHumanRelationShip alloc] init];
    rs.human = human;
    rs.family = members;
    
    return [rs autorelease];
}

- (NSString *)description
{
    return [NSString stringWithFormat:@"%@'s family's member is %@",self.human,self.family];
}
- (void)dealloc
{
    self.human = nil;
    self.family = nil;
    [super dealloc];
}

@end

int main(int argc, const char * argv[])
{
    
    HHHuman *human_0 = [HHHuman humanWithName:@"parent"];
    HHHuman *human_1 = [HHHuman humanWithName:@"lilei"];
    HHHuman *human_2 = [HHHuman humanWithName:@"hanmeimei"];
    HHHuman *human_3 = [HHHuman humanWithName:@"lewis"];
    HHHuman *human_4 = [HHHuman humanWithName:@"xiaohao"];
    HHHuman *human_5 = [HHHuman humanWithName:@"beijing"];
    

    id list = @[human_1,human_2,human_3,human_4,human_5];
    

    HHHumanRelationShip *relationShip = [HHHumanRelationShip relationShipWithHuman:human_0 family:list];
    NSLog(@"%@",relationShip);
    
    return 0;
}

NSHashTable

很明顯，大家能夠看到這樣造成了程序代碼的臃腫
根據(jù)上述需求和功能精盅，在iOS6之后帽哑，Objective-C Foundation框架中添加了兩個類分別是NSHashTable和NSMapTable

• NSHashTable
  • 構(gòu)造函數(shù)
    • - (instancetype)initWithOptions:(NSPointerFunctionsOptions)options capacity:(NSUInteger)initialCapacity
    • - (instancetype)initWithPointerFunctions:(NSPointerFunctions *)functions capacity:(NSUInteger)initialCapacity
    • + (NSHashTable *)hashTableWithOptions:(NSPointerFunctionsOptions)options;
    • + (id)hashTableWithWeakObjects;
    • + (NSHashTable *)weakObjectsHashTable;

在創(chuàng)建NSHashTable對象時，會傳NSPointerFunctionsOptions參數(shù)叹俏，列舉如下:

• NSHashTableStrongMemory
  • 將HashTable容器內(nèi)的對象引用計(jì)數(shù)+1一次
• NSHashTableZeroingWeakMemory
  • 在OSX 10.8之后已經(jīng)廢棄
• NSHashTableCopyIn
  • 將添加到容器的對象通過NSCopying中的方法妻枕，復(fù)制一個新的對象存入HashTable容器
• NSHashTableObjectPointerPersonality
  • 使用移位指針(shifted pointer)來做hash檢測及確定兩個對象是否相等；
• NSHashTableWeakMemory
  • 不會修改HashTable容器內(nèi)對象元素的引用計(jì)數(shù)，并且對象釋放后屡谐，會被自動移除

對于我們來說述么，NSHashTable吸引力比較大的即NSHashTableWeakMemory特性.
使用一段代碼來展示功能:

#import <Foundation/Foundation.h>

@interface HHHuman : NSObject

@property (nonatomic ,strong) NSString      *name;
@property (nonatomic ,strong) NSHashTable   *family;

+ (instancetype) humanWithName:(NSString *)n;

@end

@implementation HHHuman

+ (instancetype) humanWithName:(NSString *)n
{
    HHHuman *human = [[HHHuman alloc] init];
    human.name = n;
    human.family = [NSHashTable hashTableWithOptions:NSHashTableWeakMemory];
    [human.family addObject:human];

    return [human autorelease];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@'s retainCount is %lu",self.name,[self retainCount]];
}
- (void)dealloc
{
    self.name = nil;
    self.family = nil;
    [super dealloc];
}

@end

int main(int argc, const char * argv[])
{
    //創(chuàng)建一個NSHashTableWeakMemory特性的HashTable對象
    NSHashTable *hash_tab = [NSHashTable hashTableWithOptions:NSHashTableWeakMemory];

    //創(chuàng)建自動釋放池對象
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    
    //通過便利構(gòu)造器獲取一個name屬性是lewis的human對象
    HHHuman *human = [HHHuman humanWithName:@"lewis"];

    //將該對象添加到HashTable容器中
    [hash_tab addObject:human];
    
    //釋放之前打印human
    NSLog(@"before pool:%@",human);
    
    //將自動釋放池釋放掉
    [pool drain];
    
    //釋放之后打印hash_tab
    NSLog(@"after pool:%@",hash_tab);
    return 0;
}

在控制臺輸出的結(jié)果如下

before pool:lewis's retainCount is 1
after pool:NSHashTable {
}

我們可以看到，當(dāng)pool對象釋放時愕掏，human的引用計(jì)數(shù)會執(zhí)行一次-1度秘，human對象在內(nèi)存中就會自動釋放，并且相應(yīng)的hash_tab對象中的對象也會被自動移除.
而我們在創(chuàng)建hash_tab時使用的是NSHashTableStrongMemory特性話,那么控制臺輸出的結(jié)果如下:

before pool:lewis's retainCount is 2
after pool:NSHashTable {
[13] lewis's retainCount is 1
}

有了NSHashTable就可以完成我們文章一開始的需求了.

#import <Foundation/Foundation.h>

@interface HHHuman : NSObject

@property (nonatomic ,strong) NSString      *name;
@property (nonatomic ,strong) NSHashTable   *family;

+ (instancetype) humanWithName:(NSString *)n;

@end

@implementation HHHuman

+ (instancetype) humanWithName:(NSString *)n
{
    HHHuman *human = [[HHHuman alloc] init];
    human.name = n;
    human.family = [NSHashTable hashTableWithOptions:NSHashTableWeakMemory];
    [human.family addObject:human];

    return [human autorelease];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@'s retainCount is %lu",self.name,[self retainCount]];
}
- (void)dealloc
{
    self.name = nil;
    self.family = nil;
    [super dealloc];
}

@end

NSHashTable可以使用的函數(shù)

typedef struct {NSUInteger _pi; NSUInteger _si; void *_bs;} NSHashEnumerator;

FOUNDATION_EXPORT void NSFreeHashTable(NSHashTable *table);
FOUNDATION_EXPORT void NSResetHashTable(NSHashTable *table);
FOUNDATION_EXPORT BOOL NSCompareHashTables(NSHashTable *table1, NSHashTable *table2);
FOUNDATION_EXPORT NSHashTable *NSCopyHashTableWithZone(NSHashTable *table, NSZone *zone);
FOUNDATION_EXPORT void *NSHashGet(NSHashTable *table, const void *pointer);
FOUNDATION_EXPORT void NSHashInsert(NSHashTable *table, const void *pointer);
FOUNDATION_EXPORT void NSHashInsertKnownAbsent(NSHashTable *table, const void *pointer);
FOUNDATION_EXPORT void *NSHashInsertIfAbsent(NSHashTable *table, const void *pointer);
FOUNDATION_EXPORT void NSHashRemove(NSHashTable *table, const void *pointer);
FOUNDATION_EXPORT NSHashEnumerator NSEnumerateHashTable(NSHashTable *table);
FOUNDATION_EXPORT void *NSNextHashEnumeratorItem(NSHashEnumerator *enumerator);
FOUNDATION_EXPORT void NSEndHashTableEnumeration(NSHashEnumerator *enumerator);
FOUNDATION_EXPORT NSUInteger NSCountHashTable(NSHashTable *table);
FOUNDATION_EXPORT NSString *NSStringFromHashTable(NSHashTable *table);
FOUNDATION_EXPORT NSArray *NSAllHashTableObjects(NSHashTable *table);

NSMapTable

• NSMapTable
  • 構(gòu)造函數(shù)
    • - (instancetype)initWithKeyOptions:(NSPointerFunctionsOptions)keyOptions valueOptions:(NSPointerFunctionsOptions)valueOptions capacity:(NSUInteger)initialCapacity;
    • - (instancetype)initWithKeyPointerFunctions:(NSPointerFunctions *)keyFunctions valuePointerFunctions:(NSPointerFunctions *)valueFunctions capacity:(NSUInteger)initialCapacity;
    • + (NSMapTable *)mapTableWithKeyOptions:(NSPointerFunctionsOptions)keyOptions valueOptions:(NSPointerFunctionsOptions)valueOptions;
    • + (NSMapTable *)strongToStrongObjectsMapTable;
    • + (NSMapTable *)weakToStrongObjectsMapTable;
    • + (NSMapTable *)strongToWeakObjectsMapTable;
    • + (NSMapTable *)weakToWeakObjectsMapTable;

NSMapTable對象類似與NSDictionary的數(shù)據(jù)結(jié)構(gòu)亭珍，但是NSMapTable功能比NSDictionary對象要多的功能就是可以設(shè)置key和value的NSPointerFunctionsOptions特性!其他的用法與NSDictionary相同.

NSMapTable可以使用的函數(shù)

FOUNDATION_EXPORT void NSFreeMapTable(NSMapTable *table);
FOUNDATION_EXPORT void NSResetMapTable(NSMapTable *table);
FOUNDATION_EXPORT BOOL NSCompareMapTables(NSMapTable *table1, NSMapTable *table2);
FOUNDATION_EXPORT NSMapTable *NSCopyMapTableWithZone(NSMapTable *table, NSZone *zone);
FOUNDATION_EXPORT BOOL NSMapMember(NSMapTable *table, const void *key, void **originalKey, void **value);
FOUNDATION_EXPORT void *NSMapGet(NSMapTable *table, const void *key);
FOUNDATION_EXPORT void NSMapInsert(NSMapTable *table, const void *key, const void *value);
FOUNDATION_EXPORT void NSMapInsertKnownAbsent(NSMapTable *table, const void *key, const void *value);
FOUNDATION_EXPORT void *NSMapInsertIfAbsent(NSMapTable *table, const void *key, const void *value);
FOUNDATION_EXPORT void NSMapRemove(NSMapTable *table, const void *key);
FOUNDATION_EXPORT NSMapEnumerator NSEnumerateMapTable(NSMapTable *table);
FOUNDATION_EXPORT BOOL NSNextMapEnumeratorPair(NSMapEnumerator *enumerator, void **key, void **value);
FOUNDATION_EXPORT void NSEndMapTableEnumeration(NSMapEnumerator *enumerator);
FOUNDATION_EXPORT NSUInteger NSCountMapTable(NSMapTable *table);
FOUNDATION_EXPORT NSString *NSStringFromMapTable(NSMapTable *table);
FOUNDATION_EXPORT NSArray *NSAllMapTableKeys(NSMapTable *table);
FOUNDATION_EXPORT NSArray *NSAllMapTableValues(NSMapTable *table);