[iOS]NSHashTable和NSMapTable用法 - 简书
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@interfaceHHHuman:NSObject@property(nonatomic,strong)NSString*name;+ (instancetype) humanWithName:(NSString*)n;@end@implementationHHHuman+ (instancetype) humanWithName:(NSString*)n{ HHHuman *human = [[HHHuman alloc] init]; human.name= n;return[human autorelease];}- (NSString*)description{return[NSStringstringWithFormat:@"%@'s retainCount is %lu",self.name,[selfretainCount]];}- (void)dealloc{self.name=nil; [superdealloc];}@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"];idlist = @[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"];iddic = @{@"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:
@interfaceHHHuman:NSObject@property(nonatomic,strong)NSString*name;@property(nonatomic,strong)NSMutableArray*family;+ (instancetype) humanWithName:(NSString*)n;@end@implementationHHHuman+ (instancetype) humanWithName:(NSString*)n{ HHHuman *human = [[HHHuman alloc] init]; human.name= n; human.family= [[NSMutableArrayalloc] init]; [human.familyaddObject:human];return[human autorelease];}- (NSString*)description{return[NSStringstringWithFormat:@"%@'s retainCount is %lu",self.name,[selfretainCount]];}- (void)dealloc{self.name=nil;self.family=nil; [superdealloc];}@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@interfaceHHHuman:NSObject@property(nonatomic,strong)NSString*name;+ (instancetype) humanWithName:(NSString*)n;@end@implementationHHHuman+ (instancetype) humanWithName:(NSString*)n{ HHHuman *human = [[HHHuman alloc] init]; human.name= n;return[human autorelease];}- (NSString*)description{return[NSStringstringWithFormat:@"%@'s retainCount is %lu",self.name,[selfretainCount]];}- (void)dealloc{self.name=nil; [superdealloc];}@end@interfaceHHHumanRelationShip:NSObject@property(nonatomic,strong) HHHuman *human;@property(nonatomic,strong)NSArray*family;+ (instancetype)relationShipWithHuman:(HHHuman *)human family:(NSArray*)members;@end@implementationHHHumanRelationShip+ (instancetype)relationShipWithHuman:(HHHuman *)human family:(NSArray*)members{ HHHumanRelationShip *rs = [[HHHumanRelationShip alloc] init]; rs.human= human; rs.family= members;return[rs autorelease];}- (NSString*)description{return[NSStringstringWithFormat:@"%@'s family's member is %@",self.human,self.family];}- (void)dealloc{self.human=nil;self.family=nil; [superdealloc];}@endintmain(intargc,constchar* 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"];idlist = @[human_1,human_2,human_3,human_4,human_5]; HHHumanRelationShip *relationShip = [HHHumanRelationShip relationShipWithHuman:human_0 family:list];NSLog(@"%@",relationShip);return0;}
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@interfaceHHHuman:NSObject@property(nonatomic,strong)NSString*name;@property(nonatomic,strong)NSHashTable*family;+ (instancetype) humanWithName:(NSString*)n;@end@implementationHHHuman+ (instancetype) humanWithName:(NSString*)n{ HHHuman *human = [[HHHuman alloc] init]; human.name= n; human.family= [NSHashTablehashTableWithOptions:NSHashTableWeakMemory]; [human.familyaddObject:human];return[human autorelease];}- (NSString*)description{return[NSStringstringWithFormat:@"%@'s retainCount is %lu",self.name,[selfretainCount]];}- (void)dealloc{self.name=nil;self.family=nil; [superdealloc];}@endintmain(intargc,constchar* argv[]){//创建一个NSHashTableWeakMemory特性的HashTable对象NSHashTable*hash_tab = [NSHashTablehashTableWithOptions:NSHashTableWeakMemory];//创建自动释放池对象NSAutoreleasePool*pool = [[NSAutoreleasePoolalloc] 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humanNSLog(@"before pool:%@",human);//将自动释放池释放掉[pool drain];//释放之后打印hash_tabNSLog(@"after pool:%@",hash_tab);return0;}
在控制台输出的结果如下
before pool:lewis'sretainCount is1after 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'sretainCount is2after pool:NSHashTable{[13] lewis'sretainCount is1}
有了NSHashTable就可以完成我们文章一开始的需求了.
#import@interfaceHHHuman:NSObject@property(nonatomic,strong)NSString*name;@property(nonatomic,strong)NSHashTable*family;+ (instancetype) humanWithName:(NSString*)n;@end@implementationHHHuman+ (instancetype) humanWithName:(NSString*)n{ HHHuman *human = [[HHHuman alloc] init]; human.name= n; human.family= [NSHashTablehashTableWithOptions:NSHashTableWeakMemory]; [human.familyaddObject:human];return[human autorelease];}- (NSString*)description{return[NSStringstringWithFormat:@"%@'s retainCount is %lu",self.name,[selfretainCount]];}- (void)dealloc{self.name=nil;self.family=nil; [superdealloc];}@end
NSHashTable可以使用的函数
typedefstruct{NSUInteger_pi;NSUInteger_si;void*_bs;}NSHashEnumerator;FOUNDATION_EXPORTvoidNSFreeHashTable(NSHashTable*table);FOUNDATION_EXPORTvoidNSResetHashTable(NSHashTable*table);FOUNDATION_EXPORTBOOLNSCompareHashTables(NSHashTable*table1,NSHashTable*table2);FOUNDATION_EXPORTNSHashTable*NSCopyHashTableWithZone(NSHashTable*table,NSZone*zone);FOUNDATION_EXPORTvoid*NSHashGet(NSHashTable*table,constvoid*pointer);FOUNDATION_EXPORTvoidNSHashInsert(NSHashTable*table,constvoid*pointer);FOUNDATION_EXPORTvoidNSHashInsertKnownAbsent(NSHashTable*table,constvoid*pointer);FOUNDATION_EXPORTvoid*NSHashInsertIfAbsent(NSHashTable*table,constvoid*pointer);FOUNDATION_EXPORTvoidNSHashRemove(NSHashTable*table,constvoid*pointer);FOUNDATION_EXPORTNSHashEnumeratorNSEnumerateHashTable(NSHashTable*table);FOUNDATION_EXPORTvoid*NSNextHashEnumeratorItem(NSHashEnumerator*enumerator);FOUNDATION_EXPORTvoidNSEndHashTableEnumeration(NSHashEnumerator*enumerator);FOUNDATION_EXPORTNSUIntegerNSCountHashTable(NSHashTable*table);FOUNDATION_EXPORTNSString*NSStringFromHashTable(NSHashTable*table);FOUNDATION_EXPORTNSArray*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_EXPORTvoidNSFreeMapTable(NSMapTable*table);FOUNDATION_EXPORTvoidNSResetMapTable(NSMapTable*table);FOUNDATION_EXPORTBOOLNSCompareMapTables(NSMapTable*table1,NSMapTable*table2);FOUNDATION_EXPORTNSMapTable*NSCopyMapTableWithZone(NSMapTable*table,NSZone*zone);FOUNDATION_EXPORTBOOLNSMapMember(NSMapTable*table,constvoid*key,void**originalKey,void**value);FOUNDATION_EXPORTvoid*NSMapGet(NSMapTable*table,constvoid*key);FOUNDATION_EXPORTvoidNSMapInsert(NSMapTable*table,constvoid*key,constvoid*value);FOUNDATION_EXPORTvoidNSMapInsertKnownAbsent(NSMapTable*table,constvoid*key,constvoid*value);FOUNDATION_EXPORTvoid*NSMapInsertIfAbsent(NSMapTable*table,constvoid*key,constvoid*value);FOUNDATION_EXPORTvoidNSMapRemove(NSMapTable*table,constvoid*key);FOUNDATION_EXPORTNSMapEnumeratorNSEnumerateMapTable(NSMapTable*table);FOUNDATION_EXPORTBOOLNSNextMapEnumeratorPair(NSMapEnumerator*enumerator,void**key,void**value);FOUNDATION_EXPORTvoidNSEndMapTableEnumeration(NSMapEnumerator*enumerator);FOUNDATION_EXPORTNSUIntegerNSCountMapTable(NSMapTable*table);FOUNDATION_EXPORTNSString*NSStringFromMapTable(NSMapTable*table);FOUNDATION_EXPORTNSArray*NSAllMapTableKeys(NSMapTable*table);FOUNDATION_EXPORTNSArray*NSAllMapTableValues(NSMapTable*table);
文／肖浩呗（简书作者）
原文链接：http://www.jianshu.com/p/de71385930ba
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