NSDictionary&NSMutableDictionary常用操作梳理

同数组（NSArray），字典类NSDictionary也支持字面量语法糖（Object Literals Syntactic Sugar），允许我们方便地基于字面量定义初始化字典对象。以下基于字面量语法快捷初始化字典（NSDictionary）：

    NSDictionary* literalDictionary = @{@"k1":@"v1", @"k2":@"v2", @"k3":@"v3"};

需要注意的是数组是有序的，按照addObject的顺序存放；字典是无序的，在进行枚举时，读取的键－值顺序不一定和写入的顺序一致。

 1.创建初始化（Initialization&Creation）

1.1 Initializing an Dictionary(NS_DESIGNATED_INITIALIZER)

- (instancetype)init NS_DESIGNATED_INITIALIZER;

// 基于va_list初始化NSDictionary
- (instancetype)initWithObjectsAndKeys:(id)firstObject, ... NS_REQUIRES_NIL_TERMINATION;
// 基于keys数组和对应的values数组初始化NSDictionary
- (instancetype)initWithObjects:(NSArray *)objects forKeys:(NSArray *)keys;
// 基于other Dictionary初始化新的NSDictionary
- (instancetype)initWithDictionary:(NSDictionary *)otherDictionary;
- (instancetype)initWithDictionary:(NSDictionary *)otherDictionary copyItems:(BOOL)flag;

1.2 Creating an Dictionary (autorelease)

+ (instancetype)dictionary;
// 以一对key-value初始化NSDictionary
+ (instancetype)dictionaryWithObject:(id)object forKey:(id )key;
// initWithObjectsAndKeys:对应的类静态实例化方法
+ (instancetype)dictionaryWithObjectsAndKeys:(id)firstObject, ... NS_REQUIRES_NIL_TERMINATION;
// initWithObjects:forKeys:对应的类静态实例化方法
+ (instancetype)dictionaryWithObjects:(NSArray *)objects forKeys:(NSArray *)keys;
// initWithDictionary:对应的类静态实例化方法
+ (instancetype)dictionaryWithDictionary:(NSDictionary *)dict;

以下是简单的示例：

    NSDictionary* queryItemDict1 = [NSDictionary dictionaryWithObjectsAndKeys:@"v1", @"k1", @"v2", @"k2", @"v3", @"k3", nil];
    NSLog(@"queryItemDict1 = %@", queryItemDict1);
    NSDictionary* queryItemDict2 = [NSDictionary  dictionaryWithObjects:@[@"v1", @"v2", @"v3"] forKeys:@[@"k1", @"k2", @"k3"]];
    NSLog(@"queryItemDict2 = %@", queryItemDict2);

2.访问字典（Querying）

2.1 字典键值对个数

@property (readonly) NSUInteger count;

可以基于dictionary.count对字典进行判空：如果dictionary.count=0，则表示字典为nil或不包含任何键值对。

@property (readonly, copy) NSArray *allKeys; // 所有key的数组
@property (readonly, copy) NSArray *allValues; // 所有value的数组

2.2 键值索引查询

// 查找key对应的value（NSObject）
- (id)objectForKey:(id)aKey;
// 等效于objectForKey，支持中括号下标格式（dictionary[key]）访问指定键的值。
- (id)objectForKeyedSubscript:(id)key NS_AVAILABLE(10_8, 6_0);
// 查找value相同的所有keys
- (NSArray *)allKeysForObject:(id)anObject;
// 基于keys数组查找对应的values数组
- (NSArray *)objectsForKeys:(NSArray *)keys notFoundMarker:(id)marker;

以下objectsForKeys:notFoundMarker:示例：

    NSArray *keyArr = @[@"k1", @"k2", @"k3"];
    NSArray *objArr = [NSArray arrayWithObjects:@"v1", @"v2", @"v3", nil];
    NSArray *srcArr = [NSArray arrayWithObjects:@"k0", @"k2", nil];
    NSDictionary *dict = [NSDictionary dictionaryWithObjects:objArr forKeys:keyArr];
    // NSArray *resArr = [dict objectsForKeys:srcArr notFoundMarker:@"not found"]; // ("not found", v2)
    NSArray *resArr = [dict objectsForKeys:srcArr notFoundMarker:[NSNull null]]; // ("", v2)

3.遍历字典（Enumerate）

- (void)enumerateKeysAndObjectsUsingBlock:(void (^)(id key, id obj, BOOL *stop))block NS_AVAILABLE(10_6, 4_0);
- (NSSet *)keysOfEntriesPassingTest:(BOOL (^)(id key, id obj, BOOL *stop))predicate NS_AVAILABLE(10_6, 4_0);

4.字典排序（Sorting）

keysSortedByValueUsingSelector/keysSortedByValueUsingComparator通过使用指定SEL或NSComarator来对allKeys进行排序，然后通过objectsForKeys取出排序后的键－值对。

- (NSArray *)keysSortedByValueUsingSelector:(SEL)comparator;
- (NSArray *)keysSortedByValueUsingComparator:(NSComparator)cmptr NS_AVAILABLE(10_6, 4_0);

5.可变字典（NSMutableDictionary）

5.1 Initializing an Dictionary(NS_DESIGNATED_INITIALIZER)

除了继承NSDictionary基本的init，还增加了以下指定初始化函数：

- (instancetype)initWithCapacity:(NSUInteger)numItems NS_DESIGNATED_INITIALIZER;

5.2 setObject for key

// 赋值替换键值对
- (void)setObject:(id)anObject forKey:(id )aKey;
// 等效于setObject:forKey:，支持中括号下标格式（dictionary[key]=）赋值替换。
- (void)setObject:(id)obj forKeyedSubscript:(id )key NS_AVAILABLE(10_8, 6_0);

例如，以下代码片段获取URL Components查询串中的queryItem Dictionary：

    // http://weixin.sogou.com/weixin?type=2&ie=utf-8&query=NASA发现新地球
    NSString* wxNASAURLPath = @"http://weixin.sogou.com/weixin?type=2&ie=utf-8&query=NASA%E5%8F%91%E7%8E%B0%E6%96%B0%E5%9C%B0%E7%90%83";
    NSURLComponents* wxNASAURLComponents =  [NSURLComponents componentsWithString:wxNASAURLPath];
    NSMutableDictionary* queryItemDict = [NSMutableDictionary dictionary];
    NSArray* queryItems = wxNASAURLComponents.queryItems;
    for (NSURLQueryItem* item in queryItems) {
        [queryItemDict setObject:item.value forKey:item.name];
    }
    NSLog(@"queryItemDict = %@", queryItemDict);

5.3 addEntries & setDictionary

// 从otherDictionary追加entries到当前Dictionary
- (void)addEntriesFromDictionary:(NSDictionary *)otherDictionary;
// 等效于先removeAllObjects后addObjectsFromArray；setDictionary类似于对retain propery的赋值（setter）。
- (void)setDictionary:(NSDictionary *)otherDictionary;

5.4 removeObject

// 删除指定key的键值对
- (void)removeObjectForKey:(id)aKey;
// 删除指定key数组对应的键值对
- (void)removeObjectsForKeys:(NSArray *)keyArray;
// 删除清空所有键值对
- (void)removeAllObjects;

6.参考

《NSDictionary API学习》《OC字典NSDictionary》

《OC基础集合类》《Objective-C研究院之词典对象（八）》

《NSDictionary/NSMutableDictionary 及 NSArray/NSmutableArray (实例)》