java - JSlider question: Position after leftclick

Question

Whenever I click a JSlider it gets positioned one majorTick in the direction of the click instead of jumping to the spot I actually click. (If slider is at point 47 and I click 5 it'll jump to 37 instead of 5). Is there any way to change this while using JSliders, or do I have to use another datastructure?

Answer 1

As bizarre as this might seem, it's actually the Look and Feel which controls this behaviour. Take a look at BasicSliderUI, the method that you need to override is scrollDueToClickInTrack(int).

In order to set the value of the JSlider to the nearest value to where the user clicked on the track, you'd need to do some fancy pants translation between the mouse coordinates from getMousePosition() to a valid track value, taking into account the position of the Component, it's orientation, size and distance between ticks etc. Luckily, BasicSliderUI gives us two handy functions to do this: valueForXPosition(int xPos) and valueForYPosition(int yPos):

JSlider slider = new JSlider(JSlider.HORIZONTAL);
slider.setUI(new MetalSliderUI() {
    protected void scrollDueToClickInTrack(int direction) {
        // this is the default behaviour, let's comment that out
        //scrollByBlock(direction);

        int value = slider.getValue(); 

        if (slider.getOrientation() == JSlider.HORIZONTAL) {
            value = this.valueForXPosition(slider.getMousePosition().x);
        } else if (slider.getOrientation() == JSlider.VERTICAL) {
            value = this.valueForYPosition(slider.getMousePosition().y);
        }
        slider.setValue(value);
    }
});