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FAQ tweak

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Mike Thompson 2017-09-01 11:52:23 +10:00
parent 6f0ff876b0
commit 0274c784b6
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27
docs/FAQs/PollADatabaseEvery60.md
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@ -1,11 +1,9 @@
### Question
When the user switches to a certain panel, I'd like to kickoff a regular poll of my
backend (database) - say every 60 seconds.
And, then later, when the user switches away from that panel, I want to stop that polling.
backend (database) - say every 60 seconds. And, then later, when the user switches
away from that panel, I want to stop that polling.
How do I do it?
### First, An Architectural Note
@ -32,11 +30,12 @@ So, having got that out the way ...
We'll create an effect. It will be general in nature.
It will start and stop the timed/scheduled dispatch of an event. For this FAQ,
It will start and stop the timed/scheduled dispatch of an event (every 60 seconds).
For this FAQ,
this event will poll the backend but this is a general pattern
and the regularly dispatched event could do anything we wanted.
We first create an `effect` called, say, `:interval`. We must
We'll be creating an `effect` called, say, `:interval`. We must
design the data format (micro DSL) returned by an
event handler for this effect. This data format must allow an event handler to
start and stop a regular dispatch.
@ -46,22 +45,22 @@ data in this format:
```clj
{:interval {:action :start
:id :panel-1-query ;; my id for this (so I cancel later)
:frequency 60000 ;; how many millisecsbetween dispatches
:frequency 60000 ;; how many ms between dispatches
:event [:panel-query 1]}} ;; what to dispatch
```
And to later cancel the regular dispatch, an event handler would return this:
```clj
{:interval {:action :cancel
:id :panel-1-query}} ;; my id for this (provided to :start)
:id :panel-1-query}} ;; the id provided to :start
```
Now, register an effect handler for `:interval`:
Now, register an `effect handler` for the `:interval` effect:
```clj
(re-frame.core/reg-fx
:interval
(let [live-intervals (atom {})]
(fn [{:keys [action id frequency event]}]
(re-frame.core/reg-fx ;; the re-frame API for registering effect handlers
:interval ;; the effect id
(let [live-intervals (atom {})] ;; storage for live interevals
(fn [{:keys [action id frequency event]}] ;; the handler
(if (= action :start)
(swap! live-intervals assoc id (js/setInterval #(dispatch event) frequency)))
(do (js/clearInterval (get live-intervals id))
@ -70,4 +69,6 @@ Now, register an effect handler for `:interval`:
You'd probably want a bit more error checking, but that's the (untested) sketch.
### Figwheel
Figwheel is a really