键值对 key（一般为字符串对象）---vaule（必须是对象）

Person *p1 =[[Person alloc ]init];

Person *p2 =[[Person alloc ]init];

Person *p3 =[[Person alloc ]init];

NSDictionary

创建一个字典

NSDictionary *dic =@{@"p1":p1,@"p2":p2,@"p3":p3};

通过键访问值

Person *p4 = [dic objectForKey:@"p1"];

遍历字典

NSArray *allKeys = [dic allKeys];

NSLog(@"allkey: %@",allKeys);

NSArray *allValue = [dic allValues];

NSLog(@"allValue: %@",allValue);

for (NSString * key in allKeys) {

NSLog(@"%@  %@",key ,[dic objectForKey:key]);

}

获取键值对个数

NSLog(@"%ld",dic.count);

NSMutableDictionary

创建可变字典

NSMutableDictionary * dic = [NSMutableDictionary dictionaryWithCapacity:0];

添加值

[dic setObject:p1 forKey:@"p1"];

[dic setObject:p2 forKey:@"p2"];

[dic setObject:p3 forKey:@"p3"];

NSArray *allKeys = [dic allKeys];

更改某一个值

[dic setObject:p3 forKey:@"p1"];

删除某一个值

[dic removeObjectForKey:@"p1"];

全部删除值

[dic removeAllObjects];