当更新时，Om参考游标不重新呈现组件。

Question

(ns ^:figwheel-always refs-test.core
(:require [om.core :as om :include-macros true]
          [om.dom :as dom :include-macros true]
          [sablono.core :as html :refer-macros [html]]))

(enable-console-print!)

(def app-state
  (atom {:items [{:text "cat"}
             {:text "dog"}
             {:text "bird"}]
     :selected-item {}}))

(defn selected-item []
  (om/ref-cursor (:selected-item (om/root-cursor app-state))))

(defn
  selected-item-title
  [_ owner]
  (reify
    om/IRender
    (render [_]
      (html
        [:div
        (let [selected (om/observe owner (selected-item))]
          (if (empty? selected)
            [:h1 "Nothing selected"]
            [:h1 (:text selected)]))]))))

 (defn
  selected-item-button
  [item owner]
  (reify
     om/IRender
    (render [_]
      (html
       [:li
        [:button {:on-click
                  (fn []
                    (om/update! (om/root-cursor app-state) :selected-item item)                      ;; this doesn't update
                    ;;(om/update! (om/root-cursor app-state) :selected-item (merge item {:foo 1}))   ;; this does
                  )} (:text item)]]))))

(defn
  root
  [cursor owner]
  (reify
    om/IRender
    (render [_]
      (html
       [:div
        (om/build selected-item-title {})
        [:ul
         (om/build-all selected-item-button (:items cursor))]]))))


    (om/root root app-state
      {:target (.getElementById js/document "app")})

(https://www.refheap.com/108491)

(selected-item)函数将创建一个参考游标，用于跟踪app-state中的:selected-item键。当您单击一个selected-item-button时，标题会发生变化，以反映已放入映射中的新值。然而，这只起了一次作用。按下另一个按钮不会导致标题再次呈现，所以标题总是停留在您按下的第一个按钮的值。

虽然，简单地添加一个带有额外关键字的merge似乎会使它工作.(与空地图合并也不起作用，尝试过！)

我对裁判游标的理解是错误的吗？

Answer 1

所以，这个问题很简单。

(om/update! (om/root-cursor app-state) :selected-item item)

应该是

(om/update! (om/root-cursor app-state) :selected-item @item)

注意该项，因为它是一个游标，因此是取消引用的。