一、NSDictionary（不可变字典）
概述：
在编程中，字典（dictionary）是关键字及其定义的集合。NSDictionary是Cocoa中的一个集合类，它能在给定的关键字（通常是一个NSString字符串）下存储一个数值（可以是任何类型的OC对象），然后根据这个关键字来查找相应的数据。
实例方法：
//根据key查找akey对应的值
- (nullableObjectType)objectForKey:(KeyType)aKey;
//获取字典所有键值
- (NSEnumerator *)keyEnumerator;
//初始化字典
- (instancetype)init NS_DESIGNATED_INITIALIZER;
//初始化字典（根据不同的编译条件）
#if TARGET_OS_WIN32
- (instancetype)initWithObjects:(constObjectType_Nonnull[_Nullable])objects forKeys:(constKeyType_Nonnull[_Nullable])keys count:(NSUInteger)cnt;
#else
- (instancetype)initWithObjects:(constObjectType_Nonnull[_Nullable])objects forKeys:(constKeyType_Nonnull[_Nullable])keys count:(NSUInteger)cntNS_DESIGNATED_INITIALIZER;
#endif
- (nullableinstancetype)initWithCoder:(NSCoder*)aDecoderNS_DESIGNATED_INITIALIZER;
//根据所填入的object返回对应所有的key键值
- (NSArray *)allKeysForObject:(ObjectType)anObject;
//根据设置的locale进行连接数组
- (NSString*)descriptionWithLocale:(nullableid)locale;
//根据设置的locale进行连接数组
- (NSString*)descriptionWithLocale:(nullableid)locale indent:(NSUInteger)level;
//字典判断
- (BOOL)isEqualToDictionary:(NSDictionary *)otherDictionary;
//获取字典所有对象值
- (NSEnumerator *)objectEnumerator;
//字典将某个特定的数组作为key值传进去得到对应的value，如果某个key找不到对应的key，就用notFoundMarker提前设定的值代替
- (NSArray *)objectsForKeys:(NSArray *)keys notFoundMarker:(ObjectType)marker;
//将字典序列化为NSRabryType格式中指定的URL
- (BOOL)writeToURL:(NSURL*)url error:(NSError**)errorAPI_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0));
//排序
- (NSArray *)keysSortedByValueUsingSelector:(SEL)comparator;
- (void)getObjects:(ObjectType_Nonnull__unsafe_unretained[_Nullable])objects andKeys:(KeyType_Nonnull__unsafe_unretained[_Nullable])keys count:(NSUInteger)countAPI_AVAILABLE(macos(10.7), ios(5.0), watchos(2.0), tvos(9.0))NS_SWIFT_UNAVAILABLE("Use 'allKeys' and/or 'allValues' instead");
//以数组下标的形式来访问相应键的值
- (nullableObjectType)objectForKeyedSubscript:(KeyType)keyAPI_AVAILABLE(macos(10.8), ios(6.0), watchos(2.0), tvos(9.0));
//利用block对字典进行遍历
- (void)enumerateKeysAndObjectsUsingBlock:(void(NS_NOESCAPE^)(KeyType key, ObjectType obj,BOOL*stop))blockAPI_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
//利用block对字典进行遍历(添加正序反序遍历)
- (void)enumerateKeysAndObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void(NS_NOESCAPE^)(KeyType key, ObjectType obj,BOOL*stop))blockAPI_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
//根据NSComparato参数条件排序
- (NSArray *)keysSortedByValueUsingComparator:(NSComparatorNS_NOESCAPE)cmptrAPI_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
//根据NSComparato参数条件排序
- (NSArray *)keysSortedByValueWithOptions:(NSSortOptions)opts usingComparator:(NSComparatorNS_NOESCAPE)cmptrAPI_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
//过滤的方法
- (NSSet *)keysOfEntriesPassingTest:(BOOL(NS_NOESCAPE^)(KeyType key, ObjectType obj,BOOL*stop))predicateAPI_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
//过滤的方法
- (NSSet *)keysOfEntriesWithOptions:(NSEnumerationOptions)opts passingTest:(BOOL(NS_NOESCAPE^)(KeyType key, ObjectType obj,BOOL*stop))predicateAPI_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
//根据文件创建字典
- (nullableNSDictionary *)initWithContentsOfFile:(NSString*)path;
//根据url创建字典
- (nullableNSDictionary *)initWithContentsOfURL:(NSURL*)url;
//将字典写进特定的路径path
- (BOOL)writeToFile:(NSString*)path atomically:(BOOL)useAuxiliaryFile;
//将字典写进特定的url
- (BOOL)writeToURL:(NSURL*)url atomically:(BOOL)atomically;
//使用指定的以nil为结尾的对象与键对列表初始化列表
- (instancetype)initWithObjectsAndKeys:(id)firstObject, ...NS_REQUIRES_NIL_TERMINATION;
//使用另一个字典初始化字典
- (instancetype)initWithDictionary:(NSDictionary *)otherDictionary;
//使用另一个字典初始化字典，还可以为每个对象创建新的副本
- (instancetype)initWithDictionary:(NSDictionary *)otherDictionary copyItems:(BOOL)flag;
//初始化
- (instancetype)initWithObjects:(NSArray *)objects forKeys:(NSArray> *)keys;
//从指定的URL读取存储在NSpRealType格式中的字典
- (nullableNSDictionary *)initWithContentsOfURL:(NSURL*)url error:(NSError**)errorAPI_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0));
类方法：
//根据path路径获取字典信息
+ (nullableNSDictionary *)dictionaryWithContentsOfFile:(NSString*)path;
//根据url地址获取字典信息
+ (nullableNSDictionary *)dictionaryWithContentsOfURL:(NSURL*)url;
//创建字典并赋值
+ (instancetype)dictionaryWithObject:(ObjectType)object forKey:(KeyType)key;
//创建字典（根据不同编译环境）
#if TARGET_OS_WIN32
+ (instancetype)dictionaryWithObjects:(constObjectType_Nonnull[_Nullable])objects forKeys:(constKeyType_Nonnull[_Nullable])keys count:(NSUInteger)cnt;
#else
+ (instancetype)dictionaryWithObjects:(constObjectType_Nonnull[_Nullable])objects forKeys:(constKeyType_Nonnull[_Nullable])keys count:(NSUInteger)cnt;
#endif
+ (instancetype)dictionaryWithObjectsAndKeys:(id)firstObject, ...NS_REQUIRES_NIL_TERMINATIONNS_SWIFT_UNAVAILABLE("Use dictionary literals instead");
//创建字典并赋值一个字典
+ (instancetype)dictionaryWithDictionary:(NSDictionary *)dict;
//创建字典并通过数组赋值
+ (instancetype)dictionaryWithObjects:(NSArray *)objects forKeys:(NSArray> *)keys;
//从指定的URL读取存储在NSpRealType格式中的字典
+ (nullableNSDictionary *)dictionaryWithContentsOfURL:(NSURL*)url error:(NSError**)errorAPI_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0))NS_SWIFT_UNAVAILABLE("Use initializer instead");
//用来创建预订好的key集合，返回的值作为NSMutableDictionary的dictionaryWithSharesKeySet参数传入，可以重用key，从而节约copy操作，节省内存
+ (id)sharedKeySetForKeys:(NSArray> *)keysAPI_AVAILABLE(macos(10.8), ios(6.0), watchos(2.0), tvos(9.0));
//创建字典，共享键集会复用对象
+ (NSMutableDictionary *)dictionaryWithSharedKeySet:(id)keysetAPI_AVAILABLE(macos(10.8), ios(6.0), watchos(2.0), tvos(9.0));
二、NSMutableDictionary（可变字典）
概述：
和NSString和NSArray一样，NSDictionary对象是不可变。NSMutableDictionary继承至NSDictionary，允许我们随意添加、删除元素。
实例方法：
//删除字典对应key值的元素
- (void)removeObjectForKey:(KeyType)aKey;
//添加元素（anObject为要添加的元素，aKey为对应的key值）
- (void)setObject:(ObjectType)anObject forKey:(KeyType)aKey;
//初始化
- (instancetype)init NS_DESIGNATED_INITIALIZER;
//指定初始化函数
- (instancetype)initWithCapacity:(NSUInteger)numItemsNS_DESIGNATED_INITIALIZER;
- (nullableinstancetype)initWithCoder:(NSCoder*)aDecoderNS_DESIGNATED_INITIALIZER;
//字典拼接
- (void)addEntriesFromDictionary:(NSDictionary *)otherDictionary;
//删除字典
- (void)removeAllObjects;
//移除由keyArray的元素指定的key的所有数据
- (void)removeObjectsForKeys:(NSArray *)keyArray;
//设置字典内容为otherDictionary
- (void)setDictionary:(NSDictionary *)otherDictionary;
//前缀下标方法
- (void)setObject:(nullableObjectType)obj forKeyedSubscript:(KeyType)keyAPI_AVAILABLE(macos(10.8), ios(6.0), watchos(2.0), tvos(9.0));
//根据文件创建字典
- (nullableNSMutableDictionary *)initWithContentsOfFile:(NSString*)path;
//根据url创建字典
- (nullableNSMutableDictionary *)initWithContentsOfURL:(NSURL*)url;
类方法：
//初始化一个空间大小的字典(NSUInteger代表了开辟内存的一个单位)
+ (instancetype)dictionaryWithCapacity:(NSUInteger)numItems;
//根据文件获取字典信息
+ (nullableNSMutableDictionary *)dictionaryWithContentsOfFile:(NSString*)path;
//根据url地址获取字典信息
+ (nullableNSMutableDictionary *)dictionaryWithContentsOfURL:(NSURL*)url;
说明：
字典（也被称为散列表或关联数组）使用的是键查询的优化方式。它可以立即找出要查询的数据，而不需要遍历整个数组。对应大型的数据集来说，使用字典比数组要快得多，所以，这就是我们不用数组来存储然后查询的原因。