试剂输入未更新

Question

我正在尝试用Reagent/React构建一个Hello World应用程序.我使用:value/ :on-changecombo 将输入与原子绑定.但是,当我输入时,输入仍为空:

(defn new-user []
  ; Atom declared in an inner `let`.
  (let [v (atom "")]
    [:div
     [:input {:type "text"
              :value @v
              :on-change (fn [evt]
                           (reset! v (-> evt .-target .-value)))
              }]]))

(defn app [state]
  [:div
   [:p "State" (pr-str @app-state)]
   [new-user]])

(r/render-component [app app-state]
                    (.-body js/document))

如果我将原子移出let,它将起作用:

; Atom is now top-level.
(defonce v (atom ""))

(defn new-user []
  [:div
   [:input {:type "text"
            :value @v
            :on-change (fn [evt]
                         (reset! v (-> evt .-target .-value)))
            }]])

是因为v每次React重新渲染时都会重新声明？如果是这样,我如何重构该代码,以便我不必使用全局变量来保存v？

Answer 1

事实证明我很容易 - "组件"函数不能返回模板,而是返回模板的函数.这样外部函数只执行一次(我们可以放在let那里),并且内部将在每次重新渲染时执行:

(defn new-user []
  (let [v (atom "")]
    ; The returned function will be called on every re-render.
    (fn []
      [:div
       [:input {:type "text"
                :value @v
                :on-change (fn [evt]
                             (reset! v (-> evt .-target .-value)))}]])))