前言

@interface NSDictionary<__covariant KeyType, __covariant ObjectType> : NSObject 
    
         @interface NSMutableDictionary
     
       : NSDictionary
      
     
    

• 字典只能存储 OC 对象，不能存储 C 语言中的基本数据类型，也不能存储 nil 。字典中的键必须是单值的，通常它们是字符串。

• 字典对象是无序的，第一个放到词典中的键-对象对并不一定是第一个取出。

• Xcode 7 对系统中常用的一系列容器类型都增加了泛型支持（），有了泛型后就可以指定容器类中对象的类型了。假如向泛型容器中加入错误的对象，编译器会报警告。

  __covariant：协变性，子类型可以强转到父类型（里氏替换原则）。    __contravariant：逆变性，父类型可以强转到子类型。

• 不指定泛型类型的对象可以和任意泛型类型转化，但指定了泛型类型后，两个不同类型间是不可以强转的，假如你希望主动控制转化关系，就需要使用泛型的协变性和逆变性修饰符。

1、不可变字典的创建

// 直接创建不可变字典                // 字典中的 key 和 value 成对出现        NSDictionary *dic1 = @{@"key1":@"value1", @"key2":@"value2"};            // 对象方法创建                NSDictionary *dic2 = [[NSDictionary alloc] init];                    // 和 dic1 的地址不相同        NSDictionary *dic3 = [[NSDictionary alloc] initWithDictionary:dic1];            NSDictionary *dic4 = [[NSDictionary alloc] initWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];        NSDictionary *dic5 = [[NSDictionary alloc] initWithObjects:@[@"value1", @"value2", @"value3",]                                                            forKeys:@[@"key1", @"key2", @"key3"]];            // 类方法创建                    NSDictionary *dic6 = [NSDictionary dictionary];                    // 和 dic1 的地址不相同        NSDictionary *dic7 = [NSDictionary dictionaryWithDictionary:dic1];            NSDictionary *dic8 = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];        NSDictionary *dic9 = [NSDictionary dictionaryWithObject:@"value1" forKey:@"key1"];        NSDictionary *dic10 = [NSDictionary dictionaryWithObjects:@[@"value1", @"value2", @"value3",]                                                           forKeys:@[@"key1", @"key2", @"key3"]];            // 从 文件 创建字符串            NSString *path = [NSHomeDirectory() stringByAppendingString:@"/Desktop/test.txt"];                    NSDictionary *dic11 = [[NSDictionary alloc] initWithContentsOfFile:path];        NSDictionary *dic12 = [NSDictionary dictionaryWithContentsOfFile:path];                // 从 Url 创建字符串            /*            file:// 文件前缀        */            NSURL *url = [NSURL URLWithString:[@"file://" stringByAppendingString:[NSHomeDirectory()                                                       stringByAppendingString:@"/Desktop/test.txt"]]];                    NSDictionary *dic13 = [[NSDictionary alloc] initWithContentsOfURL:url];        NSDictionary *dic14 = [NSDictionary dictionaryWithContentsOfURL:url];            // 泛型创建            NSDictionary
    
      *dic15 = @{@"key1":@3, @"key2":@5};
    

2、字典中元素个数的计算

NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];            NSUInteger length = [dic count];

3、通过 key 找对应的 value

NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];            // 通过 key 找对应的 value    NSLog(@"%@", [dic objectForKey:@"key1"]);        // 以下标的方式找 key 找对应的 value    NSLog(@"%@", dic[@"key2"]);            // key 没有对应的 value 时用 notFoundMarker 参数代替    NSArray *arr = [dic objectsForKeys:@[@"key1", @"key1", @"key3"] notFoundMarker:@"not-Found"];

4、通过 value 找对应的 key

NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2",                                                                    @"key2", @"value2", @"key3", nil];            NSLog(@"%@", [dic allKeysForObject:@"value2"]);

5、字典中所有 key 的获取

NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];            NSLog(@"%@", [dic allKeys]);

6、字典中所有 value 的获取

NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];            NSLog(@"%@", [dic allValues]);

7、可变字典 NSMutableDictionary 的创建

// 对象方法创建                // 创建指定长度的字典，预先分配空间，提高效率，实际长度可大于指定长度        NSMutableDictionary *dic1 = [[NSMutableDictionary alloc] initWithCapacity:0];            // 类方法创建                // 创建指定长度的字典，预先分配空间，提高效率，实际长度可大于指定长度        NSMutableDictionary *dic2 = [NSMutableDictionary dictionaryWithCapacity:0];

8、字典中键值对的追加

NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", nil];            // 向字典末尾追加一个元素（key 值为新增的，若 key 值已存在则为修改对应的 value 值）    [dic setObject:@"value2" forKey:@"key2"];    // 向字典末尾追加一个字典    NSDictionary *dicAdd = @{@"key3": @"value3"};    [dic addEntriesFromDictionary:dicAdd];

9、字典中元素的删除

NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2",                                                                                  @"key2", @"value3", @"key3",                                                                                  @"value4", @"key4", nil];            // 删除指定的 key 对应的 value 和 key 值    [dic removeObjectForKey:@"key3"];        // 删除所有的 value 和 key 值    [dic removeAllObjects];

10、字典中元素的修改

NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2",                                                                                  @"key2", @"value3", @"key3",                                                                                  @"value4", @"key4", nil];            // 修改已存在的键值（key 值为已经存在的，若 key 值为新增的则为追加对应的 value 值）    [dic setObject:@"value5" forKey:@"key1"];        // 修改整个字典（覆盖重写)    NSDictionary *dic1 = @{@"key10":@"value10"};    [dic setDictionary:dic1];

11、字典遍历

• for 循环

  NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];    for (int i = 0; i < [dic count]; i++) {        NSLog(@"%@ = %@", [[dic allKeys] objectAtIndex:i], [dic objectForKey:[[dic allKeys] objectAtIndex:i]]);    }

• for...in 循环

  NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];    // 遍历所取出的为 key    for(id key in dic){        NSLog(@"%@ = %@", key, [dic objectForKey:key]);    }

• Block 遍历

  NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];    [dic enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {        NSLog(@"%@ = %@", key, obj);    }];

• 迭代器遍历

  NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];    // key 迭代器    NSEnumerator *keyEnumer = [dic keyEnumerator];    id key = nil;    while (key = [keyEnumer nextObject]) {        NSLog(@"%@ = %@", key, [dic objectForKey:key]);    }    // 对象迭代器    NSEnumerator *objEnumer = [dic objectEnumerator];    id obj = nil;    while (obj = [objEnumer nextObject]) {        NSLog(@"%@", obj);    }

12、字典排序

• 用指定的方法排序

  NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2",                                                                    @"value3", @"key3", @"value4", @"key4", nil];    // 先对 key 进行排序，再遍历数组    id keys1 = [dic keysSortedByValueUsingSelector:@selector(compare:)];    for (id key in keys1) {        NSLog(@"%@ = %@", key, dic[key]);    }

• 用 Block 排序

  NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2",                                                                    @"value3", @"key3", @"value4", @"key4", nil];    id keys2 = [dic keysSortedByValueUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {        return [obj1 compare:obj2];    }];    for (id key in keys2) {        NSLog(@"%@ = %@", key, dic[key]);    }