Thinking in React Implemented by Reagent

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

1. 构造恰当的数据结构
2. 从静态非交互版本开始
3. 追加交互代码

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！

1. 目标：得到符合React规范的View结构
2. 目标：得到最低标准的可交互的React应用
3. 目标：补充业务逻辑，细化交互
4. 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

 尊重原创，转载请注明转自：http://www.cnblogs.com/fsjohnhuang/p/7692956.html ^_肥仔John

参考

https://reactjs.org/docs/thinking-in-react.html