Live mapping of JavaFX ObservableList or ReactFX LiveList

Question

/**
 * An observable analogue of {@code Stream.map}. The output list is updated
 * whenever the input list changes.
 */
public static <T, R> ListBinding<R> map(
    ObservableList<? extends T> list,
    Function<T, ? extends R> mapper
);

I wrote the above JavaFX utility method which creates a live mapping of an ObservableList, updating the mapping any time the source list changes. I later discovered ReactFX and its equivalent LiveList.map:

public interface LiveList {
    default <F> LiveList<F> map(Function<? super E,? extends F> f);
}

Not wanting to reinvent the wheel again, I am now looking for a map function which returns a list of observables and automatically watches those observables. Basically a flatMap for an entire list. For instance, if I had this:

<T, R> ListBinding<R> flatMap(
    ObservableList<? extends T> list,
    Function<T, ObservableValue<? extends R>> mapper
);

Then I could do this:

ObservableList<Button>  buttons;
ObservableList<Integer> widths = flatMap(buttons, Button::widthProperty);

This widths list would grow and shrink if buttons are added or removed, and would be updated if the buttons' widths change.

Does such a function exist in JavaFX or in ReactFX? Or anything similar?

See [EasyBind](https://github.com/TomasMikula/EasyBind) (also by Tomas Mikula, who wrote ReactFX). — James_D, Apr 27 '15 at 18:53
`flatMap` for observable lists is planned for ReactFX 2.0, though with a more general signature than yours, where each list item can be mapped to an observable _list_ of items (as opposed to a single observable value). You could combine it with [Val.asList()](http://www.reactfx.org/javadoc/2.0-M4/org/reactfx/value/Val.html#asList--) for your use case. — Tomas Mikula, Apr 27 '15 at 19:01

score 2 · Accepted Answer · answered Apr 27 '15 at 22:31

I am not aware of any existing implementation of flatMap for observable lists.

It is, however, planned for ReactFX 2.0, likely with this signature

public interface LiveList {
    default <F> LiveList<F> flatMap(Function<? super E,? extends ObservableList<F>> f);
}

which is more general than what you propose: it maps an element to a list, instead of just a single value.

Live mapping of JavaFX ObservableList or ReactFX LiveList

1 Answers1