NSMutableDictionary是可变的NSDictionary,是NSDictionary的子类.

NSMutableDictionary初始化方法

• + (id)dictionaryWithCapacity:(NSUInteger)numItems
• - (id)initWithCapacity:(NSUInteger)numItems 也可以用初始化NSDictionary的方法来初始化NSMutableDictionary

NSMutableDictionary添加元素

• - (void)setDictionary:(NSDictionary *)otherDictionary //设置当前集合的元素
• - (void)setObject:(id)anObject forKey:(id<NSCopying>)aKey //添加一个键值对
• - (void)addEntriesFromDictionary:(NSDictionary *)otherDictionary //添加otherDictionary的所有元素到当前集合中

NSMutableDictionary删除元素

• - (void)removeAllObject //删除所有元素
• - (void)removeObjectForKey:(id)aKey //删除aKey对应的值
• - (void)removeObjectsForKeys:(NSArray *)keyArray //删除keyArray中所有key对应的值