活动图高阶讲解-07

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那

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刚才讲了活动

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是定义了转换的一个规则

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动作

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是活动的一个实例了

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所以呢

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我们就要有一个转换的思维

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我们要学会把

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我们的活动

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看作是

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一种转换

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这个转换包括类

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类的转换

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或者类型的转换

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如果你是面向对象的

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就是类嘛，对不对

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如果不是面向对象的

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你说是类型，也可以

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或者是状态的转换

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还是那个类

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但是状态变了

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等等

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比如说

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像这个

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我们看这个

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顾客推着购物车或

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提着篮子来到收银台

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里面很多商品

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然后呢，收银员拿起一件商品，然后把商品上的条码<br>对准扫码器，然后超市管理系统会添加一个添加项

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就这么一个简单的过程，但是这里面有很多转换的，没那么容易

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首先，第一个转换，很多商品到一件商品

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这里有一个挑一件的过程

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收银员这个人

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收银员

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他必须要从很多的商品中挑一件

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那么他大脑就做一个判断了，先拿哪一件

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他有可能拿最近那一件，离自己最近那一件，也可能先拿生鲜

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因为要考虑装袋的问题

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先把生鲜

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放上去

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对不对

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考虑装袋的问题

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那可能先判断，哪个是生鲜的，先拿生鲜的来扫码

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这里面是有一个逻辑的，如果你要画这里面的过程的话

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收银员的大脑

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他是有很多逻辑在里面的

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但不管怎么样，他是把很多商品里面挑出一件商品来

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这是一个转换

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对吧?

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好，第二个，你看

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他把商品上的条码对准扫码器

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这里面也有转换的

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输入是一件商品

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输出是提供给扫码器那个条码

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这就是一个把商品变成条码的过程

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我们可以叫亮条码

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这个实际上也不容易的

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首先，商品是摆在那里了

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拿出来了

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首先，收银员他要知道条码在哪里

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比如说，这是一盒牛奶

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那牛奶的条码在什么地方

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一般在侧面的包装

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假设是这样

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他得翻到侧面包装

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翻过来，对准扫码器

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那假设收银员都不知道什么是条码

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没有受过任何的培训

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他什么叫条码都不知道

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他能够完成扫码的任务吗

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不能的

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没准给他一个牛奶

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他把牛奶的商标对准那个扫码器扫半天

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扫不过来

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这种有的，像我们那个二维码一样嘛

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有的老头老太太

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没有用过手机的

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对不对

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跟他说

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请把你那个码对准扫码器

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他对不准的

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对不对

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因为他没有受过这些训练

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甚至有的商品，它是什么样

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它这个二维码（口误）这个条码

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是临时打出来的

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用那个条码称重仪打出来的

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特别是那个散装的商品

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对吧

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可能打出来，就随便贴在什么地方

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称重那个家伙随便一贴就贴在哪个地方

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那个收银员还得仔细地找

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到底贴在哪里了

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在这里，把这个掰出来，对准扫码器

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所以这里面有一个什么

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同样也有个逻辑在这里面

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没那么简单的

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把商品

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给你一个商品

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你把它的条码找出来

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对吧

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这又是另外一个转换

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第三个，给你一个条码

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你怎样

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把它变成一个订单项

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对不对

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在这里

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学会这样去思考

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它是这样一个转换的过程

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但我们这里都是

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比较单一的参数

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但是往往我们的参数不是那么单一

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往往是多个输入、多个输出

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现实中比这个更复杂

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我们为了举例

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特地简化了

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这个转换的思维

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就是说

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从

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控制流

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这个要有

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但是更重要的是什么

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数据转换的这种思维

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我们要学会掌握

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控制流要的

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因为控制流是这里面

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你要表示这里面怎么转换的那个要的

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但是这个

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这个思维

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更加重要

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或者说，更加有价值