How to make JavaFX Slider to move in discrete steps?

Question

I am making a GUI using JavaFx and I need sliders that only allow integers to ever be selected.

I know I can use snapToTicks, but while pulling the "knob", it can still represent a non-integer value. I would like to get rid of that. It messes up other components linked to it.

Basically, I want something like Swing's JSlider, but with JavaFx. Is it possible? I have been searching but I can't find anything.

Solution 1

You can simply add a listener to the valueProperty of the Slider and then you can either set the integer value of the new Number value:

slider.valueProperty().addListener((obs, oldval, newVal) -> 
    slider.setValue(newVal.intValue()));

or alternatively you can use integer rounding using Math.round:

slider.valueProperty().addListener((obs, oldval, newVal) ->
    slider.setValue(Math.round(newVal.doubleValue())));

Solution 2

In FXML:

<Slider fx:id="availableReproSelector" 
        blockIncrement="1.0" 
        cache="true" 
        majorTickUnit="1.0" 
        max="4.0" 
        min="1.0" 
        minorTickCount="0" 
        showTickLabels="true" 
        showTickMarks="true" 
        snapToTicks="true" 
        value="1.0" 
        />

Or in Java:

Slider slider = new Slider(1, 4, 1);
slider.setBlockIncrement(1);
slider.setMajorTickUnit(1);
slider.setMinorTickCount(0);
slider.setShowTickLabels(true);
slider.setSnapToTicks(true);

The key here is the snap to ticks option combined with a proper combination of tick units. This setting results in the following slider which can only be used to select values ranging from 1 to 4 :

Comments

[Mr Redstoner]

that's a pretty good idea, I just don't like the rounding down (for reason see my comment on SkyWalker). I still might use it though.

[DVarga]

You can also use integer rounding like ((int) Math.round(newVal.doubleValue())). Both approach just simply doesn't allow to have the "knob" between integer values.

[Mr Redstoner]

that sound way better, though I would still like to know if there is a more legitimate way.

[piegames]

Where is the praise MVC when we need it, JavaFX? Coming from Swing, this is really an ugly solution.

[DVarga]

@piegames I cannot see nothing really unforgivable in this approach (be honest - I guess you saw many much more ugly things in Swing, SWT or JavaFX or even in Winforms or WPF too;)). Some things can be done more elegantly in some of them, some thing in the other half. This approach sleeps under the aegis of simplicity, but anyways, if this solution hurts your design pattern senses, you can still implement your own Slider (skinning will be simpler in JavaFX9 as it is promised).

[kleopatra]

hmm ... always feeling dirty when changing a property in a listener (even if we seem to get away with it in fx more often than in good ol' swing). Also I would guess (didn't try) the UX to be a feel a bit unexpected which never-ever should happen. Did you (OP) try a conditional binding in the dependent controls taking the value only when the slider's adjustingProperty is false?

[Mr Redstoner]

@kleopatra Since this was for a personal project and I haven't needed it since, I've never experimented with making it better myself. Feel free to put together and post another answer. Going of of my reputation, people still sometimes stumble upon this question :)