练习与示例：

1.字典相关练习

    //查看字典中键值对个数
    NSLog(@"%lu", dic.count);
    //字典的一种遍历方式
    //查找字典中的所有key值并把它放到数组中
    NSArray *keyArray = dic.allKeys;
    //遍历数组
    for (int i = 0; i < keyArray.count; i++) {
        NSString *key = keyArray[i];
        //通过key获取value
        NSString *value = [dic objectForKey:key];
        NSLog(@"key:%@, value:%@", key, value);
    }

2.可变字典

    //创建一个空字典
    NSMutableDictionary *mutableDic = [NSMutableDictionary dictionary];
    //创建有键值对的字典
    NSMutableDictionary *mutableDic1 = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"徐博杰",@"name",@"99",@"age", nil];
    NSMutableDictionary *mutableDic2 = [@{@"name" : @"闫磊", @"age" : @"100"} mutableCopy];
    //添加
    [mutableDic setObject:@"mc海杰" forKey:@"name"];
    NSLog(@"%@", mutableDic);
    //移除
    [mutableDic removeObjectForKey:@"name"];
    NSLog(@"%@", mutableDic);
    //清空字典
    [mutableDic1 removeAllObjects];

作业：

• 新建Contact类：
• 在.h中声明属性与方法（包括初始化方法）：

@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSString *gender;
@property (nonatomic, retain) NSString *phoneNumber;
@property (nonatomic, retain) NSString *group;

- (instancetype)initWithName:(NSString *)name gender:(NSString *)gender phoneNumber:(NSString *)phoneNumber;
- (void)show;

• 导入一个自己写的获取拼音首字母的头文件和Contact类的头文件：

#import "Contact.h"
#import "NSString+EAPinYin.h"

• 在.m中进行方法的实现：

- (instancetype)initWithName:(NSString *)name gender:(NSString *)gender phoneNumber:(NSString *)phoneNumber {
    self = [super init];
    if (self) {
        _name = name;
        _gender = gender;
        _phoneNumber = phoneNumber;
        _group = name.firstCharacterForPinYinString;
    }
    return self;
}

- (void)show {
    NSLog(@"name:%@,gender:%@,phoneNumber:%@,group:%@",_name,_gender,_phoneNumber,_group);
}

• 在主函数中进行实现：

NSMutableDictionary *mutDic = [NSMutableDictionary dictionary];
        for (char c = 'A'; c <= 'Z'; c++) {
            NSString *key = [NSString stringWithFormat:@"%c",c];
            NSMutableArray *contactArr = [NSMutableArray array];
            [mutDic setObject:contactArr forKey:key];
        }
        Contact *contact = [[Contact alloc]initWithName:@"李四" gender:@"男" phoneNumber:@"123942321347"];
        //判断姓名和电话是否为空
        if (contact.name != nil && contact.name.length != 0 && contact.phoneNumber != nil && contact.phoneNumber.length != 0) {
            NSMutableArray *contactArray = [mutDic objectForKey:contact.group];
            [contactArray addObject:contact];
        } else {
            NSLog(@"姓名电话不能为空");
        }

        NSArray *keyArray = mutDic.allKeys;
        for (int i = 0; i < keyArray.count; i++) {
            NSString *key = keyArray[i];
            NSMutableArray *contactArray = [mutDic objectForKey:key];
            for (int j = 0; j < contactArray.count; j++) {
                Contact *contact = contactArray[j];
                [contact show];
                
            }
        }
    }