iOS
来源：互联网 发布：杭州恩牛网络 编辑：程序博客网 时间：2024/05/19 14:38
为什么要这么设计 ？
原因有二：
1. 每个对象创建时，都默认生成一个hashCode ,也就是一个经过哈希算法生成的一串数字 。当利用key去取字典中的value时，若是使用遍历或者二分查找等方法，效率都相对较低 ，于是出现了根据每个key生成的hashCode将该键值对放到hashCode对应的数组中的指定位置，这样当用key去取值时，便不必遍历去获取，即可以根据hashCode直接取出。
2. hashCode数字过大，或许会经过取余生成一个较小的数字，假如是对999取余，那么得到的结果始终处于0-999之间。但是，这样做的弊端在于取余所得到的值，可能是相同的，这样可能导致完全不相干的键值对被新的键值对（取余后值key相等）所覆盖。于是出现了数组中套链表实现的数组。这样，key值取余得到值相等的键值对，都将保存在同一个链表数组中，当查找key对应的值时，首先获取到该链表数组，然后遍历该数组，取正确的key所对应的值即可。
具体代码如下：
链表实现的数组
#import <Foundation/Foundation.h>@interface MYLinkedArray : NSObject@property (assign , nonatomic) NSUInteger size; - (void)addObject:(NSObject *)obj; - (void)remove:(NSObject *)obj; - (void)removeAtIndex:(NSInteger)index; - (NSObject *)objectAtIndex:(NSInteger)index; + (instancetype)array; @end@interface Node : NSObject@property (strong , nonatomic) Node *previous; @property (strong , nonatomic) Node *next; @property (strong , nonatomic) id content; @end
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. m文件
#import "MYLinkedArray.h"@interface MYLinkedArray ()@property (nonatomic, strong) Node *first; @property (nonatomic, strong) Node *last; @end@implementation MYLinkedArray- (void)addObject:(NSObject *)obj{ if (!obj) return; _size ++ ; Node *node = [[Node alloc]init]; if (!_first) { _first = node; _last = node; node.previous = nil; node.next = nil; node.content = obj; return; } node.previous = _last; node.next = nil; node.content = obj; _last = node; _last.next = node; }- (void)remove:(NSObject *)obj{ if (!obj||!_size) return; Node *tmpNode = _first; for (NSInteger index = 0; index < _size; index ++) { if ([tmpNode.content isEqual:obj]) { [self removeNode:tmpNode]; break; } }}- (void)removeAtIndex:(NSInteger)index{ if (index<0||index>=_size) return; Node *tmpNode = _first; for (NSInteger i = 0; i < _size; i ++) { if (i == index) { [self removeNode:tmpNode]; break; } tmpNode = tmpNode.next; }}- (NSObject *)objectAtIndex:(NSInteger)index{ if (index<0||index>=_size) return nil; Node *tmpNode = _first; for (NSInteger i = 0; i < _size; i ++) { if (i == index) { return tmpNode.content; } tmpNode = tmpNode.next; } return nil;}- (void)removeNode:(Node *)node{ Node *preNode = node.previous; Node *nextNode = node.next; preNode.next = nextNode; nextNode.previous = preNode; node.content = nil; _size -- ;}+ (instancetype)array{ return [[self alloc]init];}@end@implementation Node@end
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自定义的字典类
#import <Foundation/Foundation.h>@interface MYDictionary : NSObject+ (instancetype)dictionary;- (void)setValue:(id)value forkey:(NSString *)key;- (id)valueForKey:(NSString *)key;@end
. m文件
#import "MYDictionary.h"#import "MYLinkedArray.h"@interface KeyValueCache : NSObject@property (nonatomic, strong) NSString *key;@property (nonatomic, strong) id value;@end@implementation KeyValueCache+ (instancetype)key:(NSString *)key value:(id)value{ KeyValueCache *model = [[self alloc]init]; model.key = key; model.value = value; return model;}@end@interface MYDictionary ()@end@implementation MYDictionary{ MYLinkedArray *_keyValues[999];}+ (instancetype)dictionary{ return [[self alloc]init];}- (void)setValue:(id)value forkey:(NSString *)key{ NSUInteger hash = key.hash; NSUInteger realCode = hash%(sizeof(_keyValues)/8); MYLinkedArray *linkArr = _keyValues[realCode]; if (linkArr) { for (NSInteger index = 0; index < linkArr.size; index ++) { KeyValueCache *keyValue = (KeyValueCache *)[linkArr objectAtIndex:index]; if ([keyValue.key isEqualToString:key]) { keyValue.value = value; return; } } KeyValueCache *newKeyValue = [KeyValueCache key:key value:value]; [linkArr addObject:newKeyValue]; }else{ MYLinkedArray *newLinkArray = [MYLinkedArray array]; KeyValueCache *newKeyValue = [KeyValueCache key:key value:value]; [newLinkArray addObject:newKeyValue]; _keyValues[realCode] = newLinkArray; }}- (id)valueForKey:(NSString *)key{ if (!key.length) return nil; NSUInteger hash = key.hash; NSUInteger realCode = hash%(sizeof(_keyValues)/8); MYLinkedArray *linkArr = _keyValues[realCode]; if (linkArr) { for (NSInteger index = 0; index < linkArr.size; index ++) { KeyValueCache *keyvalue = (KeyValueCache *)[linkArr objectAtIndex:index]; if ([keyvalue.key isEqualToString:key]) { return keyvalue.value; } } } return nil;}@end
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最终实验结果：
- (void)viewDidLoad { [super viewDidLoad]; MYDictionary *dict = [MYDictionary dictionary]; [dict setValue:@"哈哈" forkey:@"孟"]; [dict setValue:@"你好" forkey:@"孟"]; [dict setValue:@123456 forkey:@"数字"]; NSLog(@"%@",[dict valueForKey:@"孟"]); NSLog(@"%@",[dict valueForKey:@"数字"]);}
成功自定义了一个字典.
