本文对 Foundation 框架中的字典类（NSDictionary 和 NSMutableDictionary）的使用做一个详细的总结。

1. NSDictionary

1.1 NSDictionar 介绍

• Dictionary翻译过来叫做"字典"
• 日常生活中，“字典”的作用：通过一个拼音或者汉字，就能找到对应的详细解释
• NSDictionary的作用类似：通过一个键（key），就能找到对应的值（value）
• NSDictionary中的键（key）是单值，通常是字符串，也可以是其他对象类型
• NSDictionary中和键（key）关联的值（value）可以是任何对象类型，但不能是nil
• NSDictionary是不可变的，一旦初始化完毕，里面的内容就无法修改

1.2 NSDictionary 的创建

+ (instancetype)dictionary;
+ (instancetype)dictionaryWithObject:(id)object forKey:(id <NSCopying>)key;
+ (instancetype)dictionaryWithObjectsAndKeys:(id)firstObject, ...;
+ (id)dictionaryWithContentsOfFile:(NSString *)path;
+ (id)dictionaryWithContentsOfURL:(NSURL *)url;

1.3 NSDictionary 创建和获取简写

• 以前 NSDictionary 创建方式

NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:@"Walkers", @"name", @"12345678", @"phone", @"ZhongGuo", @"address", nil];
NSDictionary *dict = [NSDictionary dictionaryWithObjects:@[@"Walkers",@"30",@"1.75"] forKeys:@[@"name",@"age",@"height"]];

• 现在 NSDictionary 创建简写方式

NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};

• 以前NSDictionary获取元素方式

[dict objectForKey:@"name”];

• 现在NSDictionary获取元素简写方式

dict[@"name”];

1.4 键值对集合的特点

• 字典存储的时候，必须是"键值对"的方式来存储(同时键不要重复)
• 键值对中存储的数据是"无序的"
• 键值对集合可以根据键，快速获取数据

1.5 NSDictionary 的遍历

• 返回字典的键值对数目- (NSUInteger)count;

NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
NSLog(@"count = %lu",[dict count]);

输出结果：count = 3

• 根据key取出value- (id)objectForKey:(id)aKey;

NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
NSLog(@"%@",[dict objectForKey:@"name"]);

输出结果：Walkers

• 快速遍历

NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};

for (NSString *key in dict) {
    NSLog(@"key = %@, value = %@", key, dict[key]);
}

输出结果：
key = name, value = Walkers
key = phone, value = 12345678
key = address, value = ZhongGuo

• Block遍历

[dict enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
    NSLog(@"key = %@, value = %@", key, obj);
}];

1.6 NSDictionary 文件操作

• 将字典写入文件中
  • - (BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFile;
  • - (BOOL)writeToURL:(NSURL *)url atomically:(BOOL)atomically;
  • 存储结果是xml文件格式，但苹果官方推荐为plist后缀
• 示例

NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};

BOOL flag = [dict writeToFile:@"/Users/Walkers/Desktop/dict.plist" atomically:YES];
NSLog(@"flag = %i", flag);

输出结果：flag = 1

文件里的内容显示结果如下图

• 从文件中读取字典

NSDictionary *newDict = [NSDictionary dictionaryWithContentsOfFile:@"/Users/Walkers/Desktop/dict.plist"];
NSLog(@"newDict = %@", newDict);

1.7 NSDictionary 和 NSArray 对比

1.7.1 NSDictionary 和 NSArray 的区别

• NSArray是有序的，NSDictionary是无序的
• NSArray是通过下标访问元素，NSDictionary是通过key访问元素

1.7.2 NSDictionary 和 NSArray 的用法

• 创建

// 数组
@[@"Walkers", @"Rose"] (返回是不可变数组)
// 字典
@{ @"name" : @"Walkers", @"phone" : @"12345678" } (返回是不可变字典)

• 访问

// 数组
id d = array[1];
// 字典
id d = dict[@"name"];

• 赋值

// 数组
array[1] = @"Walkers";
// 字典
dict[@"name"] = @"Walkers";

---

2. NSMutableDictionary

2.1 NSMutableDictionary 介绍

• NSMutableDictionary是NSDictionary的子类
• NSDictionary是不可变的，一旦初始化完毕后，它里面的内容就永远是固定的，不能删除里面的元素，也不能再往里面添加元素
• NSMutableDictionary是可变的，随时可以往里面添加\更改\删除元素

2.2 NSMutableDictionary 的常见操作

• 添加/修改一个键值对(如果aKey之前有值，则会把aKey之前对应的值给替换掉)- (void)setObject:(id)anObject forKey:(id <NSCopying>)aKey;

NSMutableDictionary *dict = [NSMutableDictionary  dictionary];

[dict setObject:@"Walkers" forKey:@"name"];
NSLog(@"%@", dict);

输出结果：
{
    name = Walkers;
}

NSMutableDictionary *dict = [NSMutableDictionary  dictionary];

[dict setObject:@"Walkers" forKey:@"name"];
NSLog(@"%@", dict);

[dict setObject:@"abc" forKey:@"name"];
NSLog(@"%@", dict);

输出结果：
{
    name = Walkers;
}
{
    name = abc;
}

• 通过aKey删除对应的value- (void)removeObjectForKey:(id)aKey;

NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setValuesForKeysWithDictionary: @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"}];

[dict removeObjectForKey:@"name"];
NSLog(@"%@",dict);

输出结果：
{
    address = ZhongGuo;
    phone = 12345678;
}

• 删除所有的键值对- (void)removeAllObjects;

NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setValuesForKeysWithDictionary: @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"}];

[dict removeAllObjects];
NSLog(@"%@",dict);

输出结果：
{
}

2.3 NSMutableDictionary 的简写

• 以前设置键值对方式

[dict setObject:@"Jack" forKey:@"name”];

• 现在设置键值对方式

dict[@"name"] = @"Jack";