黑马程序员---OC学习笔记之NSDictionary的介绍及使用

——Java培训、Android培训、iOS培训、.Net培训——–

1、NSDictionary介绍

NSDictionary 的作用类似：通过一个key，就能找到对应的value。它是不可变的，一旦初始化完毕，其内容就无法被修改

而且字典是无序的。

2、创建

//NSDictionary介绍与使用
        //1）创建字典，一旦创建，内容就不可改变
        //空字典
        NSDictionary *dic1 = [NSDictionary dictionary];

        //2）创建只有一个键值对的字典
        NSDictionary *dic2 = [NSDictionary dictionaryWithObject:@"Amos" forKey:@];
        NSLog(@"dic2 = %@",dic2);
        //3）创建有多个键值对的字典
        //【注意】字典的key和value都必须是OC对象不能是基础数据类型
        //方式一：NSDictionary *dic3 = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"Amos",@"Allen",@"Andy", nil]forKeys:[NSArray arrayWithObjects:@"1",@"2",@"3", nil]];
        //方式二：
        NSDictionary *dic3 = [NSDictionary dictionaryWithObjectsAndKeys:@"Amos",@"1",@"Allen",@"2", nil];
        NSLog(@"dic1 = %@",dic3);

        //4）快速创建字典
        //@{key:vaule}
        NSDictionary *dic4 = @{@: @"Amos",@: @"Allen",@: @"Andy"};
        NSLog(@"dic1 = %@",dic4);
           

3、字典的特点

1）字典的key是不能重复的，如果重复了将不会被添加到字典

2）键值对存储数据是无序的

3）键值对集合可以根据key快速获取数据

4、基本用法

1）获取地点键值对个数，即字典长度

- (NSUInteger)count;

例如：

NSUInteger count = dic4.count;

2）根据key值去value

NSString *name = [dic4 objectForKey:@1];

NSLog(@”name = %@”,name);

5、字典的遍历

NSDictionary *dic4 = [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"Amos",@"2", @"Allen",@"3", @"Andy", nil];
        //遍历字典
        //1）普通方法：先获取key，再根据key获取value
        for (NSString *key in dic4) {

            NSLog(@"key = %@ value = %@",key,[dic4 objectForKey:key]);
        }
        //2）block遍历
        [dic4 enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
            NSLog(@"key = %@ value = %@",key,obj);
        }];
           

2015-10-08 12:00:53.410 DictionaryDemo[3832:303] key = Amos value = 1

2015-10-08 12:00:53.412 DictionaryDemo[3832:303] key = Allen value = 2

2015-10-08 12:00:53.413 DictionaryDemo[3832:303] key = Andy value = 3

2015-10-08 12:00:53.413 DictionaryDemo[3832:303] key = Amos value = 1

2015-10-08 12:00:53.414 DictionaryDemo[3832:303] key = Allen value = 2

2015-10-08 12:00:53.414 DictionaryDemo[3832:303] key = Andy value = 3