Anyone who has seen the subject implemented in Java/Swing might have
been stunned by the hundreds of lines of code that were deemed
necessary for it, with their appropriate share of bugs. (And an
implementation I've seen in C#/NetAdvantage was even worse, which was
less related to the language itself, as to the GUI toolkit)
I knew this could be done way more elegant, but I was surprised it can
be done THIS nicely - if done in clojure. And if you think this can be
improved further or find any bugs, shoot!
Example: Prices for Japanese stock have a step size of
1 in the interval [0,3000],
5 in the interval (3000,5000],
...
An easy way to model that would be a sorted map:
(def japanese-stock-tick-map
(sorted-map
0 1
3000 5
5000 10
30000 50
50000 100
300000 500
500000 1000
3000000 5000
5000000 10000
30000000 50000
50000000 100000))
Figuring out the step size - which on the interval edges depends on
whether you go up or down - can be done like this:
(defn get-tick-size
[tick-map value go-up?]
(second (first (rsubseq tick-map (if go-up? <= <) value))))
Aligning an arbitrary value to the closest valid number (if
necessary):
(defn align-to-tick-size
[tick-map value]
(let [tick-size (get-tick-size tick-map value false)
remainder (mod value tick-size)]
(if (zero? remainder)
value
(* tick-size ((if (>= remainder (/ tick-size 2)) inc identity)
(quot value tick-size))))))
Now implementing the SpinnerModel is trivial (which is why I will not
copy it here, but leave it on http://dueck.org/tick/tick-size-spinner.html
in a simple demo for anyone to try out).
You're the man, Rich!
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