字典——NSDictionary

1.什么是字典

字典是一种保存键值对（key - value）的容器。

注意：一个 key 对应一个 value（实体），而一个 value 可以对应多个 key

2.创建字典对象

字典的输入格式——值左键右

//类方法
NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:@"a", @"name", @"ab", @"sex", @"ac", @"address", nil];
NSLog(@"%@", dictionary);
//对象方法
NSDictionary *dictionary1 = [[NSDictionary alloc] initWithObjectsAndKeys:@"b", @"name", @"bc", @"sex", @"bd", @"address", nil];
NSLog(@"%@", dictionary1);
//创建空的字典
NSDictionary *dictionary2 = [NSDictionary dictionary];

3.获取所有key值

NSLog(@"%@", dictionary.allKeys);

4.获取所有value值

NSLog(@"%@", dictionary.allValues);

5.根据key查value

NSLog(@"%@", [dictionary objectForKey:@"name"]);
//  根据值查询所有键
NSLog(@"%@", [dictionary allKeysForObject:@"a"]);

6.间接遍历字典

根据allkeys数组获取字典中所有的key-value对

for (NSString *key in dictionary.allKeys) {
NSLog(@"%@", [dictionary objectForKey:key]);
}

7.NSMutableDictionary

//初始化
NSMutableDictionary *mubDic = [NSMutableDictionary dictionary];
NSMutableDictionary *mubDic1 = [NSMutableDictionary dictionary];

8.添加键值对

[mubDic setObject:@"a" forKey:@"ad"];
[mubDic setObject:@"b" forKey:@"be"];
[mubDic1 setObject:@"a" forKey:@"ad"];
[mubDic1 setObject:@"b" forKey:@"be"];
NSLog(@"%@", mubDic);

9.修改key对应的value

本质上为重新赋值

[mubDic setObject:@"b" forKey:@"ad"];
[mubDic setObject:@"a" forKey:@"be"];
NSLog(@"%@", mubDic);

10.删除键值对

//删除对应 key 的 value
[mubDic removeObjectForKey:@"be"];
NSLog(@"%@", mubDic);
//根据 key 的数组删除对应 value
[mubDic1 removeObjectsForKeys:mubDic1.allKeys];
//删除所有
[mubDic removeAllObjects];
NSLog(@"%@", mubDic);
NSLog(@"%@", mubDic1);