Allow registration and de-registration of post event callbacks via an id.

CHANGES.md

@@ -113,7 +113,8 @@ Joking aside, this is a substantial release which will change how you use re-fra
 ##### Improvements
 
   - Bug fix: `post-event-callbacks` were not called when `dispatch-sync` was called.
-  - added new API `re-frame.core/remove-post-event-callback`. See doc string.
+  - added new API `re-frame.core/clear-post-event-callback` which de-registers a callback 
+    added by `re-frame.core/add-post-event-callback`
   - when an event-handler makes no change to `app-db`, the `debug` middleware now logs a
     single line saying so, rather than a "group".  Makes it slightly easier to grok
     the absence of change.

src/re_frame/core.cljc

@@ -87,18 +87,22 @@
     - you want to create your own handling infrastructure, with perhaps multiple
       handlers for the one event, etc.  Hook in here.
     - libraries providing 'isomorphic javascript' rendering on  Nodejs or Nashorn.
+
+  'id' is typically a keyword.
   "
-  [f]
-  (router/add-post-event-callback re-frame.router/event-queue f))
+  ([f]
+    (router/add-post-event-callback re-frame.router/event-queue f f))
+  ([id f]
+   (router/add-post-event-callback re-frame.router/event-queue id f)))
 
 
 (defn remove-post-event-callback
-  [f]
-  (router/remove-post-event-callback re-frame.router/event-queue f))
+  [id]
+  (router/remove-post-event-callback re-frame.router/event-queue id))
 
 
-;; --  Helpful Message
-;; Assisting the v0.0.7 ->  v0.0.8 tranistion.  Remove in v0.0.9
+;; --  Deprecation Messages
+;; Assisting the v0.0.7 ->  v0.0.8 tranistion.
 (defn register-handler
   [& args]
   (console :warn  "re-frame:  \"register-handler\" has been renamed \"reg-event\"")

src/re_frame/router.cljc

@@ -69,7 +69,7 @@
 
   ;; -- API
   (push [this event])
-  (add-post-event-callback [this f])
+  (add-post-event-callback [this id callack])
   (remove-post-event-callback [this f])
 
   ;; -- Implementation via a Finite State Machine
@@ -97,12 +97,14 @@
   (push [this event]         ;; presumably called by dispatch
     (-fsm-trigger this :add-event event))
 
-  (add-post-event-callback [_ callback-fn]
-    ;; register a callback function which will be called after each event is processed
-    (set! post-event-callback-fns (conj post-event-callback-fns callback-fn)))
+  ;; register a callback function which will be called after each event is processed
+  (add-post-event-callback [_ id callback-fn]
+    (->> (assoc post-event-callback-fns id callback-fn)
+         (set! post-event-callback-fns)))
 
-  (remove-post-event-callback [_ callback-fn]
-    (set! post-event-callback-fns (remove #(= % callback-fn) post-event-callback-fns)))
+  (remove-post-event-callback [_ id]
+    (->> (dissoc post-event-callback-fns id)
+         (set! post-event-callback-fns)))
 
 
   ;; -- FSM Implementation ---------------------------------------------------