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前言：本文将要讲述的内容有 1.NSDictionary 以及 NSMutableDictionary 概述 2.常用属性方法举例（不常用的本文不会涉及）
一 NSDictionary/NSMutableDictionary概述 NSDictionary提供了一种key－value的数据存储方式。总的来说，任何对象都可以作为key，只要其遵循NSCopying协议。其中，key不能相同（由isEqual来判断）。key和value都不能为nil，如果要表达一个空的值，用NSNull。NSDictionary中的值不可变。 NSMutableDictionary是NSDictionary的子类，是可变的字典。
二 NSDictionary常用的属性方法举例
2.1 创建和初始化 创建兼初始化
(instancetype)dictionaryWithContentsOfFile:(NSString *)path(instancetype)dictionary;(instancetype)dictionaryWithDictionary:(NSDictionary *)(*)keys(instancetype)dictionaryWithObjectsAndKeys:(id)firstObject
初始化
-(NSDictionary *)init;-(NSDictionary *)initWithContentsOfFile:(NSString *)path;-(NSDictionary *)initWithDictionary:(NSDictionary *);-(NSDictionary *)initWithObjects:(NSArray *)objects forKeys:(NSArray *)keys;-(NSDictionary *)initWithObjectsAndKeys:(id)firstObject;
就个人而言，我比较习惯后一种。当然，快捷创建的方式不要忘记了 符号
@{}
举例：
NSDictionary * emptyDic = [NSDictionary dictionary];NSDictionary * firstDic = @{@”key”:@”value”,@”first”:@”1″};NSDictionary * secondDic = [[NSDictionary alloc] initWithObjectsAndKeys:@”value1″,@”key1″,@”value2″,@”key2″,nil];
2.2 count 返回key－value对的个数
NSDictionary * dic = @{@”key1″:@”1″,@”key2″:@”2″};NSLog(@”%d”,dic.count);
2.3 isEqualToDictionary比较两个dictionary内容是否一样。
NSDictionary * dic1 = @{@”key1″:@”1″,@”key2″:@”2″};NSDictionary * dic2 = @{@”key2″:@”2″,@”key1″:@”1″};if ([dic1 isEqualToDictionary:dic2]) {NSLog(@”Equal contents”);}
2.4 objectForKey: 和valueForKey 由属性获得内容
NSDictionary * dic1 = @{@”key1″:@”1″,@”key2″:@”2″};NSLog(@”%@”,[dic1 objectForKey:@”key1″]);NSLog(@”%@”,[dic1 valueForKey:@”key2″]);
2.5 allKeys 和 allValues 获得所有的key/value
NSDictionary * dic1 = @{@”key1″:@”1″,@”key2″:@”2″};NSArray * keys = [dic1 allKeys];NSArray * values = [dic1 allValues];
2.6 enumerateKeysAndObjectsUsingBlock 用Block的方式遍历
这里的stop决定了是否停止遍历。NSDictionary * dic1 = @{@”key1″:@”1″,@”key2″:@”2″};[dic1 enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {NSLog(@”%@=>%@”,[key description],[obj description]);}];
2.7 排序 keysSortedByValueUsingSelector: keysSortedByValueUsingComparator : keysSortedByValueWithOptions: usingComparator: 返回Keys的数组，，顺序按照value排序顺序。
NSDictionary * numsDic = @{@(2):@”second”,@(1):@”first”,@(3):@”thrid”};NSDictionary * strDic = @{@”id_1″:@”first”,@”id_3″:@”thrid”,@”id_2″:@”second”};NSArray * numsSortedKeys = [numsDic keysSortedByValueUsingSelector:@selector(compare:)];NSArray * strSortedKyes = [strDic keysSortedByValueUsingComparator:^NSComparisonResult(id obj1, id obj2) {NSString * str1 = obj1;NSString * str2 = obj2;return [str1 compare:str2];}];NSLog(@”%@”,numsSortedKeys.description);NSLog(@”%@”,strSortedKyes.description);
输出
2015-02-09 22:04:12.070 DictonaryExample[1037:23292] ( 1, 2, 3 ) 2015-02-09 22:04:12.070 DictonaryExample[1037:23292] ( “id_1”, “id_2”, “id_3” )
2.8 过滤 keysOfEntriesPassingTest： 返回keys的集合，这些keys符合参数block的约束
NSDictionary * numsDic = @{@(2):@”second”,@(1):@”first”,@(3):@”thrid”}; NSSet * filteredKyes = [numsDic keysOfEntriesPassingTest:^BOOL(id key, id obj, BOOL *stop) {BOOL result = NO;NSNumber * numKey = key;if (numKey.integerValue > 2) {result = YES;}return result;}];NSLog(@”%@”,filteredKyes.description);
输出
2015-02-09 22:09:50.800 DictonaryExample[1099:25241] {( 3 )}
绊住的不仅是双脚，还有未来。
