最近有个新需求，就是做下电商App基本都有的功能-足迹，简单的说不就是浏览记录嘛。设计图是下面这样滴！

我的足迹列表.png

看上去设计图也很正常，该有的都有了，只要数据没问题，基本就是写下界面就over了，万万没想到，问题就出现在这数据上，所有数据竟然是客户端自己存，自己取，完完全全的一个本地浏览记录啊😭，既然需求确定是这样了，那就没办法只能开始了。

存数据

数据怎么存呢？下面几种数据持久化方案都行：

• plist文件
• NSUserDefaults
• NSKeyedArchiver
• 数据库
• CoreData
  这里由于赶时间就偷了个懒，选用了NSUserDefaults 来存储数据（应该首选数据库和CoreData）。
  然后需要存一些什么数据呢？业务需要，我们每条数据都需要有commodityId（商品id），commodityInfoId（商品信息sku），scanTime（商品浏览时间）。由于商品id是唯一的，这里我就采用了字典key的唯一性来进行去重，只保留最新的浏览记录。

- (NSMutableDictionary *)commodityDic {
    if (!_commodityDic) {
        _commodityDic = [NSMutableDictionary dictionaryWithDictionary:[self.storageDic objectForKey:@"用户userId"];
    }
    return _commodityDic;
}
- (NSMutableArray *)commodityArray {
    if (!_commodityArray) {
        _commodityArray = [NSMutableArray array];
    }
    return _commodityArray;
}

NSString *insetStr = [NSString stringWithFormat:@"%@|%@", scanTime,commodityInfoId];
[self.commodityDic setObject:insetStr forKey:commodityId];   
[self.storageDic setObject:self.commodityDic forKey:@"用户userId"];
[[NSUserDefaults standardUserDefaults] setObject:self.storageDic forKey:@"你的key"];
[[NSUserDefaults standardUserDefaults] synchronize];
//两个字典的结构是这样的：
self.commodityDic {
    ZMCOMD132170419142301330 = "2017-11-14 17:56:49|ZMCOMD132170419142301330170419142301304";
    ZMCOMD426170808141848800 = "2017-11-14 15:05:35|ZMCOMD426170808141848800170808141848472";
    ZMCOMD881170710143358733 = "2017-11-14 17:48:46|ZMCOMD881170710143358733170710143358515";
    ZMCOMD956171018164822665 = "2017-11-14 17:48:39|ZMCOMD956171018164822665171018164822894";
}
self.storageDic
{
    16050368695640 =     {
        ZMCOMD233170802151805643 = "2017-11-14 10:30:02|647060";
        ZMCOMD593170208112702710 = "2017-11-14 10:29:57|ZMCOMD593170208112702710170208112702912";
    };
    17091455092851 =     {
        ZMCOMD132170419142301330 = "2017-11-14 17:56:49|ZMCOMD132170419142301330170419142301304";
        ZMCOMD426170808141848800 = "2017-11-14 15:05:35|ZMCOMD426170808141848800170808141848472";
        ZMCOMD881170710143358733 = "2017-11-14 17:48:46|ZMCOMD881170710143358733170710143358515";
        ZMCOMD956171018164822665 = "2017-11-14 17:48:39|ZMCOMD956171018164822665171018164822894";
    };
}

好了，数据这样就算是存上了😀。

取数据

//根据用户id来取数据
NSMutableDictionary *disorderlyDic = [self.storageDic objectForKey@"用户userId"];
    NSArray *keysArray = disorderlyDic.allKeys;
    NSArray *valuesArray = disorderlyDic.allValues;
    //按时间进行排序
    NSArray *sortArray = [valuesArray sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
        return [obj2 compare:obj1 options:NSNumericSearch];
    }];
    NSMutableArray *orderlyArray = [NSMutableArray array];
    for (NSInteger i = 0; i < sortArray.count; i++) {
        NSInteger index = [valuesArray indexOfObject:sortArray[i]];
        NSString *key = keysArray[index];
        NSString *value = sortArray[i];
        [orderlyArray addObject:@{key:value}];
    }
//按时间排序后的数据是这样的
sortArray
<__NSArrayI 0x60800024f9f0>(
2017-11-14 17:56:49|ZMCOMD132170419142301330170419142301304,
2017-11-14 17:48:46|ZMCOMD881170710143358733170710143358515,
2017-11-14 17:48:39|ZMCOMD956171018164822665171018164822894,
2017-11-14 15:05:35|ZMCOMD426170808141848800170808141848472
)
orderlyArray
<__NSArrayM 0x60800005b7e0>(
{
    ZMCOMD132170419142301330 = "2017-11-14 17:56:49|ZMCOMD132170419142301330170419142301304";
},
{
    ZMCOMD881170710143358733 = "2017-11-14 17:48:46|ZMCOMD881170710143358733170710143358515";
},
{
    ZMCOMD956171018164822665 = "2017-11-14 17:48:39|ZMCOMD956171018164822665171018164822894";
},
{
    ZMCOMD426170808141848800 = "2017-11-14 15:05:35|ZMCOMD426170808141848800170808141848472";
}
)

数据合并，排序

//将时间相同的合并在一起
NSDictionary *commodityAllDic = [NSMutableDictionary dictionary];
for (NSInteger i = 0; i < orderlyArray.count; i ++) {
    NSDictionary *comDic = self.commodityArray[i];
    NSString *comTime = [[comDic.allValues[0] componentsSeparatedByString:@"|"][0] substringWithRange:NSMakeRange(0, 10)];
     NSMutableArray *array = [self.commodityAllDic objectForKey:comTime];
      if (!array) {
          array =[NSMutableArray array];
      }
     [array addObject:comDic.allKeys[0]];
     [commodityAllDic setObject:array forKey:comTime]; 
}
//按时间排序
NSArray *keyArray = [self.commodityAllDic allKeys];
NSArray *sortArray = [keyArray sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
      return [obj2 compare:obj1 options:NSNumericSearch];
}];
//数据结构是这样的
commodityAllDic
{
    "2017-11-14" =     (
        ZMCOMD132170419142301330,
        ZMCOMD881170710143358733,
        ZMCOMD956171018164822665,
        ZMCOMD426170808141848800
    );
}
sortArray
<__NSSingleObjectArrayI 0x60800001d7c0>(
2017-11-14
)

做到这一步数据处理基本完事了，有sortArray，我们可以取到commodityAllDic对应的commodityId,根据commodityId，我们可以取到存取的数据。

删除数据

这个就简单了

- (void)removeCommodityWithCommodityId:(NSMutableArray *)commodityIdArray {
    for (NSString *commodityId in commodityIdArray) {
        [self.commodityDic removeObjectForKey:commodityId];
    }
    [self.storageDic setObject:self.commodityDic forKey:@"用户userId"];
    [[NSUserDefaults standardUserDefaults] setObject:self.storageDic forKey:@"你的key"];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

分页加载数据

上面的几个都搞定了，这个也比较简单了，确定每一页需要显示的个数，从排序后orderlyArray中依次取出相对应的个数，然后按照数据合并，排序的方法，来进行整合数据。