Java SWT Slider.getMaximum() equals 100, but you can only drag it up to 90

Question

If you create a Slider (org.eclipse.swt.widgets.Slider) then call getMaximum() on it, the value is 100. But when you actually try dragging the Slider to its maximum value, it only reaches 90.

I can work round this problem:

sl.setSelection(sl.getMaximum());   // sl.getMaximum() is 100   
int actualMax = sl.getSelection();  // should be 100, but is actually 90

But something definitely seems to be wrong, no?

Etalon

Check the width of the slider (the increment). I'm guessing that the slider stops before the maximum to include the increment. – Leacock

Answer 1

As you know Slider is nothing but ScrollBar widget,the maximum value that you set is equal to max_value+thumb_value value.

Try this code:

  final Slider slider = new Slider(shell, SWT.NONE);
  slider.setMaximum(100);
  slider.setMinimum(0);
  slider.setThumb(20);

  slider.addSelectionListener(new SelectionListener() {

    @Override
    public void widgetSelected(SelectionEvent e) {
        System.out.println( slider.getSelection()  +"   "+ slider.getThumb());
    }

    @Override
    public void widgetDefaultSelected(SelectionEvent e) {

      // TODO Auto-generated method stub

    }
  });

Thermoelectricity

I didn't know that. But thank you. So the maximum value you can actually drag the slider to is sl.getMaximum() - sl.getThumb(). I still think it would be much more natural for the maximum value you can drag it to to be sl.getMaximum(). – Etalon

Answer 2

I can also observe this behavior on Windows 7 with SWT 3.6.1 and SWT 4.2.1.

A simple but somehow dissatisfying workaround would be to use:

sl.setMaximum(110);

Then the values range from 0 to 100.

Ammadas

This does not work in general (since it depends on the thumb value - see my answer for details). – Satyr

Also, the middle of the slider will now be 55. – Udelle

Answer 3

Although the provided answers helped to solve the problem, it still took a while for me to implement it correctly. If you want to make the values 0-100 selectable with your slider, you should do:

// we want to have the values 0-100
slider.setMaximum(100 + slider.getThumb());
// this now returns the selected value, which can be from 0-100
slider.getSelection();

Satyr