Clojure and JavaFX 2 -- passing multiple-arity arguments to JavaFX methods

Question

A lot of JavaFx methods take var args, such as Group, which is declared in Java as:

public Group(Node... children)

Others for example:

public KeyFrame(Duration time, KeyValue... values)

I've discovered the ... means I should pass a java array to the method, so I've been doing stuff like this,

(-> timeline .getKeyFrames 
  (.addAll 
    (into-array [(KeyFrame. blabla) (KeyFrame. blabla)]))`

It's annoying to have to do (into-array...) every time there is a var arg, and it's more annoying when the var arg is a base class of what I'm actually passing in. For example

(Group. (into-array [(Circle. 100) (Rectangle. 100 100)]))

results in type mismatch error. Instead I have to do this:

(Group. (into-array Node [(Circle. 100) (Rectangle. 100 100)]))

So i made this function:

(defn make-group [& items]
  (Group. (into-array Node items)))

which is fine for Groups, but doesn't solve the general problem.

So is there a nice way of solving the ellipses/vararg problem so I don't have to make special functions for each vararg method? The requirements for this function would be that it take the method you want to call (eg Group), the fixed args, the var args, and somehow magically the function would know to find the common base class of the elements in the var args.

Thanks

score 2 · Answer 1 · answered May 29 '13 at 12:12

2

Have you tried putting the arguments in a vector? I haven't tried all the use cases you mention, but when using the addAll() method for example I just put the arguments into a literal vector, e.g.

    (.addAll (.getChildren btn-pane) [new-puzzle-pane check-box hint-btn
                                  check-btn solve-btn load-btn save-btn
                                  print-btn about-btn spacer])

answered May 29 '13 at 12:12

clartaq

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passing vectors directly was what I tried first and got `Wrong number of args (0) passed to: PersistentVector` – Sonicsmooth May 29 '13 at 19:14

score 1 · Answer 2 · answered May 29 '13 at 19:17

I wound up using a macro, which I kind of suspected I needed:

(defmacro jvar [method & args]
  (let [lastargs (last args)
        evaled-lastargs (eval lastargs)]
    (if (coll? evaled-lastargs)
      (let [firstargs (butlast args)
            klass (eval (last firstargs))
            supset (map #(supers (class %)) evaled-lastargs)
            common (apply intersection #{klass} supset)]
        (if (seq common)
          `(~method ~@(butlast firstargs) (into-array ~(first common) ~lastargs))
          `(~method ~@firstargs (into-array ~lastargs)))))))

Usage like this:

(jvar Group. Node [(Circle. 100) (Rectangle. 10 10)])

Clojure and JavaFX 2 -- passing multiple-arity arguments to JavaFX methods

2 Answers2