前言
本文是学习Thinking in React这一章后的记录，并且用Reagent实现其中的示例。
概要
一、构造恰当的数据结构
Since you’re often displaying a JSON data model to a user, you’ll find that if your model was built correctly, your UI (and therefore your component structure) will map nicely.
VDom让我们可以将Model到View的映射交出，而更专注于数据和数据结构本身，即是折腾数据和数据结构才是我们的主要工作。因此我们要设计出与View中组件结构对应的数据结构，然后将不符合该数据结构的数据做一系列转换，然后将数据交给React就好了。
居上所述那么可以知道，数据结构就依赖View的结构，那么如何设计View的结构呢？是采用Top-down还是Bottom-up的方式呢？对于小型应用我们直接采用Top-down即可，对于大型应用则采用Bottom-up更合适。（根据过往经验将大规模的问题域拆分成多个小规模的问题域，然后对小问题域采用Top-down方式，若无法直接采用Top-down方式则继续拆分，然后将多个小问题域的值域组合即可得到大问题域的值域）
无论是Top-down还是Bottom-up方式，都要将View构建为树结构（这很符合DOM结构嘛）。因此得到如下结构
FilterableProductTable
|_SearchBar
|_ProductTable
|_ProductCategoryRow
|_ProductRow
而数据则从顶层View组件往下流动，各层提取各自数据进行渲染。
二、从静态非交互版本开始
It’s best to decouple these processes because building a static version requires a lot of typing and no thinking, and adding interactivity requires a lot of thinking and not a lot of typing.
从设计(他人或自己)那得到设计稿或HTML模板，我们就可以开始着手重构模板、添加交互效果和填充业务逻辑和服务端交互等功能了。且慢，我们先不着急动手，而是要先分清工作步骤，才能有条不紊地包质保量工作哦！
- 目标：得到符合React规范的View结构
- 目标：得到最低标准的可交互的React应用
- 目标：补充业务逻辑，细化交互
- 目标：连接远程数据源，细化交互
(ns demo.core
(:require [reagent.core :as re])
(def products [
{:category "Sporting Goods", :price "$49.99", :stocked true, :name "Football"}
{:category "Sporting Goods", :price "$9.99", :stocked true, :name "Baseball"}
{:category "Sporting Goods", :price "$29.99", :stocked false, :name "Basketball"}
{:category "Electronics", :price "$99.99", :stocked true, :name "iPod Touch"}
{:category "Electronics", :price "$399.99", :stocked false, :name "iPhone 5"}
{:category "Electronics", :price "$199.99", :stocked true, :name "Nexus 7"}
])
(declare <filterable-product-table>
<search-bar>
<product-table>
<product-category-row>
<product-row>)
(declare get-rows)
(defn <filterable-product-table>
[products]
[:div
[<search-bar>]
[<product-table> products]])
(defn <search-bar>
[]
[:form
[:input {:placeholder "Search..."}]
[:input {:type "checkbox"}]
"Only show products in stock."])
(defn <product-table>
[products]
[:table
[:thead
[:tr
[:th "Name"]
[:th "Price"]]]
[:tbody
(get-rows products)]])
(defn assemble-rows
[products]
(reduce
(fn [{:keys [cate] :as rows-info} product]
(let [curr-cate (:category product)
curr-rows (if (not= curr-cate cate)
(list ^{:key curr-cate}[<product-category-row> curr-cate])
(list))
rows (cons ^{:key (:name product)} [<product-row> product] curr-rows)]
(-> rows-info
(assoc :cate curr-cate) ;; 更新cate值
(update
:rows
(fn [o rows]
(concat rows o))
rows)))) ;; 更新rows值
{:cate nil :rows '()}
products))
(defn get-rows
[products]
(-> (assemble-rows products)
:rows
reverse))
(defn <product-category-row>
[cate]
[:tr
[:td {:colSpan 2} cate]])
(defn <product-row>
[product]
[:tr
[:td (when (:stocked product) {:style {:color "red"}})
(:name product)]
[:td (:price product)]])
这一步我们并没有提供交互功能，因此只会用到prop传递数据，绝对不会用到state的。而交互的意思是，对View的操作会影响应用数据，从而刷新View。
三、追加交互代码
交互实质上就是触发View状态变化，那么就必须提供一种容器来暂存当前View的状态，而这个在React就是state了。
(ns demo.core
(:require [reagent.core :as re])
(def products [
{:category "Sporting Goods", :price "$49.99", :stocked true, :name "Football"}
{:category "Sporting Goods", :price "$9.99", :stocked true, :name "Baseball"}
{:category "Sporting Goods", :price "$29.99", :stocked false, :name "Basketball"}
{:category "Electronics", :price "$99.99", :stocked true, :name "iPod Touch"}
{:category "Electronics", :price "$399.99", :stocked false, :name "iPhone 5"}
{:category "Electronics", :price "$199.99", :stocked true, :name "Nexus 7"}
])
(declare <filterable-product-table>
<search-bar>
<product-table>
<product-category-row>
<product-row>)
(declare get-rows
validate-product)
(defn <filterable-product-table>
[products]
(let [search-text (re/atom "")
stocked? (re/atom false)
on-search-text-change #(reset! search-text (.. % -target -value))
on-stocked?-change #(reset! stocked? (.. % -target -checked))]
(fn []
[:div
[<search-bar> on-search-text-change on-stocked?-change]
[<product-table> (filter (partial validate-product @search-text @stocked?) products)]])))
(defn validate-product
[search-text stocked? product]
(and (if stocked? (:stocked product) true)
(as-> search-text %
(re-pattern (str "(?i)" %))
(re-find % (:name product)))))
(defn <search-bar>
[on-search-text-change on-stocked?-change]
[:form
[:input {:placeholder "Search..."
:onChange on-search-text-change}]
[:input {:type "checkbox"
:onChange on-stocked?-change}]
"Only show products in stock."])
(defn <product-table>
[products]
[:table
[:thead
[:tr
[:th "Name"]
[:th "Price"]]]
[:tbody
(get-rows products)]])
(defn assemble-rows
[products]
(reduce
(fn [{:keys [cate] :as rows-info} product]
(let [curr-cate (:category product)
curr-rows (if (not= curr-cate cate)
(list ^{:key curr-cate}[<product-category-row> curr-cate])
(list))
rows (cons ^{:key (:name product)} [<product-row> product] curr-rows)]
(-> rows-info
(assoc :cate curr-cate) ;; 更新cate值
(update
:rows
(fn [o rows]
(concat rows o))
rows)))) ;; 更新rows值
{:cate nil :rows '()}
products))
(defn get-rows
[products]
(-> (assemble-rows products)
:rows
reverse))
(defn <product-category-row>
[cate]
[:tr
[:td {:colSpan 2} cate]])
(defn <product-row>
[product]
[:tr
[:td (when (:stocked product) {:style {:color "red"}})
(:name product)]
[:td (:price product)]])
注意：reagent中使用state时，需要定义一个返回函数的高阶函数来实现。
(defn <statefull-cmp> [data]
(let [local-state (re/atom nil)
on-change #(reset! local-state (.. % -target -value))]
(fn []
[:div
[:input {:onChange on-change}]
[:span @local-state]])))
(re/render [<statefull-cmp> 1]
(.querySelector js/document "#app"))
总结
参考
https://reactjs.org/docs/thinking-in-react.html
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