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NSHashTable和NSMapTable用法

2016-05-09 15:54 162 查看


转载自：简书 http://www.jianshu.com/p/de71385930ba

一个项目中的需求

在iOS项目开发过程中，我们经常会使用到
NSSet
、
NSArray
、
NSDictionary
三个类，它们为我们设计较友好的数据结构时提供了很方便的方法先准备本文中将要使用的对象:
#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
在程序开发过程中,经常会用到诸如此类的
Model
对象.用法呢也大致会有如下几种方式:1.通过有序的数列进行存储,数组
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);
输出的结果如下:
(
"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.通过统一的关键字进行存储,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};
//同样在控制台输出上文字典，用来查看每个对象的保留值
NSLog(@"%@",list);
输出的结果如下:
(
"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"
)
通过上述两个例子我们能够发现一个问题，即
将对象添加到容器时，会对该对象的引用技术+1
这样就会有可能发生循环持有的问题，例如如下代码:
@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
在以上代码中,一个
human
的实例对象中包含一个
strong
修饰的
family
属性，但是在
family
属性中，又添加了
human
自身对象，这样会造成循环持有的问题，而导致内存泄漏。但是项目需求又要求我们在该
Model
对象中完成如此代码，我们不得已会多创建一个类
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

很明显，大家能够看到这样造成了程序代码的臃肿根据上述需求和功能，在iOS6之后，
Objective-C Foundation
框架中添加了两个类分别是
NSHashTable
和
NSMapTable
NSHashTable
构造函数
- (instancetype)initWithOptions:(NSPointerFunctionsOptions)options
capacity:(NSUInteger)initialCapacity

- (instancetype)initWithPointerFunctions:(NSPointerFunctions
*)functions capacity:(NSUInteger)initialCapacity

+ (NSHashTable *)hashTableWithOptions:(NSPointerFunctionsOptions)options;

+ (id)hashTableWithWeakObjects;

+ (NSHashTable *)weakObjectsHashTable;
在创建
NSHashTable
对象时，会传
NSPointerFunctionsOptions
参数，列举如下:
NSHashTableStrongMemory
将HashTable容器内的对象引用计数+1一次
NSHashTableZeroingWeakMemory
在OSX 10.8之后已经废弃
NSHashTableCopyIn
将添加到容器的对象通过
NSCopying
中的方法，复制一个新的对象存入
HashTable
容器
NSHashTableObjectPointerPersonality
使用移位指针(shifted pointer)来做hash检测及确定两个对象是否相等；
NSHashTableWeakMemory
不会修改HashTable容器内对象元素的引用计数，并且对象释放后，会被自动移除对于我们来说，
NSHashTable
吸引力比较大的即
NSHashTableWeakMemory
特性.使用一段代码来展示功能:
#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[])
{
//创建一个NSHashTableWeakMemory特性的HashTable对象
NSHashTable *hash_tab = [NSHashTable hashTableWithOptions:NSHashTableWeakMemory];

//创建自动释放池对象
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

//通过便利构造器获取一个name属性是lewis的human对象
HHHuman *human = [HHHuman humanWithName:@"lewis"];

//将该对象添加到HashTable容器中
[hash_tab addObject:human];

//释放之前打印human
NSLog(@"before pool:%@",human);

//将自动释放池释放掉
[pool drain];

//释放之后打印hash_tab
NSLog(@"after pool:%@",hash_tab);
return 0;
}
在控制台输出的结果如下
before pool:lewis's retainCount is 1
after pool:NSHashTable {
}
我们可以看到，当
pool
对象释放时，
human
的引用计数会执行一次
-1
，human对象在内存中就会自动释放，并且相应的
hash_tab
对象中的对象也会被自动移除.而我们在创建
hash_tab
时使用的是
NSHashTableStrongMemory
特性话,那么控制台输出的结果如下:
before pool:lewis's retainCount is 2
after pool:NSHashTable {
[13] lewis's retainCount is 1
}
有了
NSHashTable
就可以完成我们文章一开始的需求了.
#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可以使用的函数

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
构造函数
- (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
对象类似与
NSDictionary
的数据结构，但是
NSMapTable
功能比
NSDictionary
对象要多的功能就是可以设置
key
和
value
的NSPointerFunctionsOptions特性!其他的用法与
NSDictionary
相同.


NSMapTable可以使用的函数

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);


                                            

                                        

                        
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