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前言：本文將要講述的內容有
1.NSDictionary 以及 NSMutableDictionary 概述
2.常用屬性方法舉例（不常用的本文不會涉及）

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一 NSDictionary/NSMutableDictionary概述
NSDictionary提供了一種key－value的數據存儲方式。總的來說，任何對象都可以作為key，只要其遵循NSCopying協議。其中，key不能相同（由isEqual來判斷）。key和value都不能為nil，如果要表達一個空的值，用NSNull。NSDictionary中的值不可變。
NSMutableDictionary是NSDictionary的子類，是可變的字典。

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二 NSDictionary常用的屬性方法舉例

2.1 創建和初始化
創建兼初始化

(instancetype)dictionaryWithContentsOfFile:(NSString *)path
(instancetype)dictionary;
(instancetype)dictionaryWithDictionary:(NSDictionary *)
(instancetype)dictionaryWithObjects:(NSArray *)objects   forKeys:(NSArray *)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;

就個人而言，我比較習慣後一種。當然，快捷創建的方式不要忘記了
符號

@{}

舉例：

    NSDictionary * emptyDic = [NSDictionary dictionary];
    NSDictionary * firstDic = @{@"key":@"value",
                                @"first":@"1"};
    NSDictionary * secondDic = [[NSDictionary alloc] initWithObjectsAndKeys:@"value1",@"key1",@"value2",@"key2",nil];

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2.2 count
返回key－value對的個數

    NSDictionary * dic = @{@"key1":@"1",
                           @"key2":@"2"};
    NSLog(@"%d",dic.count);

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2.3 isEqualToDictionary比較兩個dictionary內容是否一樣。

    NSDictionary * dic1 = @{@"key1":@"1",
                           @"key2":@"2"};
    NSDictionary * dic2 = @{@"key2":@"2",
                            @"key1":@"1"};
    if ([dic1 isEqualToDictionary:dic2]) {
        NSLog(@"Equal contents");
    }

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2.4 objectForKey: 和valueForKey 由屬性獲得內容

    NSDictionary * dic1 = @{@"key1":@"1",
                           @"key2":@"2"};
    NSLog(@"%@",[dic1 objectForKey:@"key1"]);
    NSLog(@"%@",[dic1 valueForKey:@"key2"]);

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2.5 allKeys 和 allValues 獲得所有的key/value

    NSDictionary * dic1 = @{@"key1":@"1",
                           @"key2":@"2"};
    NSArray * keys = [dic1 allKeys];
    NSArray * values = [dic1 allValues];

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2.6 enumerateKeysAndObjectsUsingBlock 用Block的方式遍歷

這裡的stop決定了是否停止遍歷。
NSDictionary * dic1 = @{@"key1":@"1",
                           @"key2":@"2"};
[dic1 enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        NSLog(@"%@=>%@",[key description],[obj description]);
    }];

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2.7 排序
keysSortedByValueUsingSelector:
keysSortedByValueUsingComparator :
keysSortedByValueWithOptions: usingComparator:
返回Keys的數組，順序按照value排序順序。

  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);

輸出

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”
)

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2.8 過濾
keysOfEntriesPassingTest：
返回keys的集合，這些keys符合參數block的約束

  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);

輸出

2015-02-09 22:09:50.800 DictonaryExample[1099:25241] {(
3
)}

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2.9寫到文件
writeToFile:atomically
writeToURL:atomically

   NSString * path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject] ;
    NSString * fileName = @"file";
    NSString * filePath = [path stringByAppendingPathComponent:fileName];

    NSDictionary * dic = @{@"key":@"value"};
    BOOL result = [dic writeToFile:filePath atomically:YES];
    if (result) {
        NSLog(@"Success");
    }

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2.10Description－常常用來debug輸出dictionary的內容。
在之前已經舉例好多了，這裡不再贅述

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三 NSMutableDictionary的額外方法
3.1 添加元素

- (void)setObject:(id)anObject
           forKey:(id)aKey
- (void)setValue:(id)value
          forKey:(NSString *)key
- (void)setDictionary:(NSDictionary *)otherDictionary

注意，使用KVC的時候，key一定要是NSString。第三個函數是刪除之前的元素，然後把otherDictionary元素放到當前dic中。
舉例

    NSMutableDictionary * dic = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"object",@"key", nil];
    NSLog(@"%@",dic.description);
    [dic setDictionary:@{@"otherKey":@"otherValue"}];
    NSLog(@"%@",dic.description);

輸出

2015-02-09 22:31:21.417 DictonaryExample[1232:31666] {
key = object;
}
2015-02-09 22:31:21.418 DictonaryExample[1232:31666] {
otherKey = otherValue;
}

3.2刪除元素

- (void)removeObjectForKey:(id)aKey
- (void)removeAllObjects
- (void)removeObjectsForKeys:(NSArray *)keyArray

比較容易忽視的是第三個，刪除一組key。
舉例

 NSDictionary * dic = @{@(1):@"first",
                           @(2):@"second",
                           @(3):@"thrid"};
    NSMutableDictionary * mutableDic = [[NSMutableDictionary alloc] initWithDictionary:dic];
    [mutableDic removeObjectsForKeys:@[@(1),@(2)]];
    NSLog(@"%@",mutableDic.description);

輸出

2015-02-09 22:34:13.112 DictonaryExample[1273:32793] {
    3 = thrid;
}

BTY：年前計劃在更新一篇KVC 和 KVO的詳細講解。然後繼續更新GCD系列的第五篇。如果精力夠用的話，更再更新一篇Swift相關的。