1.创建字典

// 1.如何创建
    NSDictionary *dict = [NSDictionary dictionaryWithObject:@"lnj" forKey:@"name"];
    NSString *name = [dict objectForKey:@"name"];
    NSLog(@"name = %@", name);
    
//  注意: key和value 是一一对应
    NSDictionary *dict = [NSDictionary dictionaryWithObjects:@[@"lnj", @"30", @"1.75"] forKeys:@[@"name", @"age", @"height"]];
    NSLog(@"%@ %@ %@", [dict objectForKey:@"name"], [dict objectForKey:@"age"], [dict objectForKey:@"height"]);
    
    NSDictionary *dict = @{key:value};
    NSDictionary *dict = @{@"name": @"lnj"};
    NSLog(@"%@", dict[@"name"]);
    
    NSDictionary *dict = @{@"name":@"lnj", @"age":@"30", @"height":@"1.75"};
    NSLog(@"%@ %@ %@", dict[@"name"], dict[@"age"], dict[@"height"]);

2.字典的遍历

(1)普通遍历

for (int i = 0; i < dict.count; ++i) {
         获取字典中所有的key
        NSArray *keys = [dict allKeys];
         取出当前位置对应的key
        NSLog(@"%@", keys[i]);
        NSString *key = keys[i];
        NSString *value = dict[key];
        NSLog(@"key = %@, value = %@", key, value);
    }

（2）快速遍历

    // 如何通过forin遍历字典, 会将所有的key赋值给前面的obj
    for (NSString *key in dict) {
        NSLog(@"%@", key);
        NSString *value = dict[key];
        NSLog(@"key = %@, value = %@", key, value);

    }

(3) 用迭代器遍历

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

3.字典文件读写

 // 3.字典文件读写
    NSDictionary *dict = @{@"name":@"lnj", @"age":@"30", @"height":@"1.75"};
    // XML 扩展名plist
    [dict writeToFile:@"/Users/xiaomage/Desktop/info.plist" atomically:YES];
    
    // 注意: 字典和数组不同, 字典中保存的数据是无序的
    NSDictionary *newDict = [NSDictionary dictionaryWithContentsOfFile:@"/Users/xiaomage/Desktop/info.plist"];
    NSLog(@"%@", newDict);