iOS的KVC妙用举例

KVC在iOS开发中是绝不可少的利器，这种基于运行时的编程方式极大地提高了灵活性，简化了代码，KVC算是iOS开发的一种黑魔法。

使用场景举例：
如果想要将以下的所有merchantType字段存成一个不可变的数组，以备用

{
    "code": "000000",
    "data": {
        "businessInfos": [{
            "distance": "561.32",
            "businessId": "BD2017102109081500069783",
            "businessName": "丽马体验店",
            "businessAreaName": "市辖区",
            "merchantType": "CF99",
        }, {
            "distance": "1553.78",
            "businessId": "BD2017070611050100012749",
            "businessName": "麦克咖啡",
            "businessAreaName": "秀洲区",
            "merchantType": "BK",
        }, {
            "distance": "1593.86",
            "businessId": "BD2017070611022200012748",
            "businessName": "大麦客直销中心",
            "businessAreaName": "秀洲区",
            "merchantType": "WD",
            "businessImage": "http://fdfs.xylbn.cn/group1/M00/05/38/wKgthloFRsaAB9oKAAAZ_LoHwQM515.png"
        }, {
            "distance": "1596.76",
            "businessId": "BD2017082315125500057012",
            "businessName": "阿拉丁麻辣烫",
            "businessAreaName": "市辖区",
            "merchantType": "CF1",
            "businessImage": "http://fdfs.xylbn.cn/group1/M00/02/44/wKgthVlUrIeAZ60_AAC-VaUFHrc830.png"
        }, {
            "distance": "1596.99",
            "businessId": "BD2017082315264300057032",
            "businessName": "玛丽莲甜品（嘉兴万达店）",
            "businessAreaName": "市辖区",
            "merchantType": "CF3",
        }, {
            "distance": "1597.01",
            "businessId": "BD2017082314390700056966",
            "businessName": "小淮娘",
            "businessAreaName": "桐乡市",
            "merchantType": "CF4",
        }]
    },
    "msg": "执行成功"
}

常规的方法：

    self.shopArray=[[[self dictionaryWithContentsOfJSONString:@"shop.json"] objectForKey:@"data"] objectForKey:@"businessInfos"];

    NSMutableArray * merchantTypeArrMutableArr = [NSMutableArray array];
    for(NSDictionary *dict in self.shopArray){
        NSString * str = dict[@"merchantType"];
        [merchantTypeArrMutableArr addObject:str];
    }
    NSArray * merchantTypeArr = [NSArray arrayWithArray: merchantTypeArrMutableArr];

    NSLog(@"%@ merchantTypeArr", merchantTypeArr);

巧妙的方法：

    self.shopArray=[[[self dictionaryWithContentsOfJSONString:@"shop.json"] objectForKey:@"data"] objectForKey:@"businessInfos"];

    NSArray * merchantTypeArr = [self.shopArray valueForKey:@"merchantType"];

    NSLog(@"%@ merchantTypeArr", merchantTypeArr);

如果还想获取每个merchantType字段的一些属性，比如字符长度，然后生成数组，同样可以一行代码搞定：

    NSArray* merchantTypeLengthArr = [merchantTypeArr valueForKeyPath:@"length"];
    NSLog(@"%@ merchantTypeLengthArr", merchantTypeLengthArr);

再复杂点的场景也能极简处理，比如再求出所有merchantType字段字符的总长度

        NSNumber* merchantTypeAllLength= [merchantTypeLengthArr valueForKeyPath:@"@sum.self"];
        NSLog(@"%@ merchantTypeAllLength", merchantTypeAllLength);