IOS学习之NSDictionary和NSMutableDictionary详解

字典的操作是根据键和值的操作，一个key有相对应的value的存在，也就是说通过key值我们可以找到相对应的value

ok ,我们先来学习下不可变的NSDictionary

创建字典

+（instancetype）dictionary //creates and return an empty dictionary

有时候我们将字典的信息放入文件中，我们需要将我们所需要的信息取出可以采用

+（NSDictionary *）dictionaryWithContentsOfFile:(NSString *)path

//creates and returns a dictionary using the keys and values found in a file specified by a given path

当然有时候也可以根据特定的URL来获取字典信息

+（NSDictionary *）dictionaryWithContentsOfURL:(NSURL *)url

//creates and return a dictionary using the kyes and values founds in a resource specified by a given URl

在更多的初始化过程中我们一般直接将键和值都写出来

+（instancetype）dictionaryWithObjectsAndKeys:(id)firstObject

eg:

NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value",@"key",nil];

//creates and returns a dictionary containing entries consturcted form the specified set of values and keys

计数项

在开发过程中，我们经常需要知道字典中的数量

@property（readonly）NSUinteger count

//the number of entries in the dictionary

字典比较

-（bool）isEqualToDictionary:(NSDictionary *)otherDictionary

//Returns a Boolean value that indicates whether the contents of receiving dictionary are eaual to the contents of another given dictionary

访问键和值

@property(readonly,copy)NSArray *allKeys

//a new array containing the dictionary's keys or an empty array if the dictionary has no entries

@property(readonly,copy)NSArray *allValues

// A new array containing the dictionary's value or an empty array if the dictionary has no entries

//在操作过程中我们往往需要通过键值来查找相对应的vlaue

-(id)objectForKey:(id)key

//returns the value associates with a given key

枚举字典

当你想通过枚举的方式获得所有键的时候可以采用

-（NSEnumerator *）keyEnumerator

//returns an emumerator object that lets you access each key in the dictionary

所有对象的枚举对象

-（NSEmumerator *）objectEnumerator

//Returns an emunerator object that let youy access each value in the dictionary

存储字典

-（BOOL）writeToFile:(NSString *)path atomacially:(BOOL)flag

//writes a property list representation of the contents of the dictionary to given path

-(bool)writeToUrl:(NSURL *)aURL atomatically:(BOOL)flag

//Writes a property list representation of the contents of the dictionary to given URL

下面来接收NSMutableDictionary

首先创建和初始化的过程和NSDictionary一样处理

接下来我们要处理的是添加和删除的操作

添加操作

-(void)setObject:(id)anObject  forKey:(id)akey

//Adds a given key-vlaue pair to dictionary

删除操作

-(void)removeObjectForKey(id)akey

//Removes a given key and its associated value from the dictionary

-(void)removeAllObjects

//Empties the dictionary of its entries