java - JScrollBar:最大值较小时旋钮不可见

Question

我想创建一个水平滚动条，其最大值设置为2(它应该只允许选择0、1或2作为值)，但如果该值小于11，旋钮是不可见的。

    scrlLineDist = new JScrollBar();
    scrlLineDist.setBlockIncrement(1);
    scrlLineDist.addAdjustmentListener(new AdjustmentListener() {
        public void adjustmentValueChanged(AdjustmentEvent e) {
            System.out.println(scrlLineDist.getValue());
        }
    });
    GridBagConstraints gbc_scrlLineDist = new GridBagConstraints();
    gbc_scrlLineDist.insets = new Insets(0, 0, 5, 0);
    gbc_scrlLineDist.fill = GridBagConstraints.HORIZONTAL;
    gbc_scrlLineDist.gridx = 0;
    gbc_scrlLineDist.gridy = 3;
    panel_4.add(scrlLineDist, gbc_scrlLineDist);
    scrlLineDist.setMaximum(2);
    scrlLineDist.setToolTipText("");
    scrlLineDist.setOrientation(JScrollBar.HORIZONTAL);

当我将最大值值更改为12时，它按照我想要的方式工作(可见旋钮，值[0,2])。为什么会发生这种情况？

    scrlLineDist = new JScrollBar();
    scrlLineDist.setBlockIncrement(1);
    scrlLineDist.addAdjustmentListener(new AdjustmentListener() {
        public void adjustmentValueChanged(AdjustmentEvent e) {
            System.out.println(scrlLineDist.getValue());
        }
    });
    GridBagConstraints gbc_scrlLineDist = new GridBagConstraints();
    gbc_scrlLineDist.insets = new Insets(0, 0, 5, 0);
    gbc_scrlLineDist.fill = GridBagConstraints.HORIZONTAL;
    gbc_scrlLineDist.gridx = 0;
    gbc_scrlLineDist.gridy = 3;
    panel_4.add(scrlLineDist, gbc_scrlLineDist);
    scrlLineDist.setMaximum(12);
    scrlLineDist.setToolTipText("");
    scrlLineDist.setOrientation(JScrollBar.HORIZONTAL);

Answer 1

您正在寻找的可能是 JSlider ，而不是 JScrollbar。

// orientation, min, max, initial value
final JSlider slider = new JSlider(SwingConstants.HORIZONTAL, 0, 2, 1);
slider.setSnapToTicks(true); // only allow 0, 1, 2 and not in between
slider.setPaintTicks(true); // paint ticks at tick spacing interval
slider.setMajorTickSpacing(1); // set interval to 1
slider.setPaintLabels(true); // show labels on ticks

向 slider 添加一个 ChangeListener，而不是 AdjustmentListener，如下所示:

slider.addChangeListener(new ChangeListener() {

    @Override
    public void stateChanged(ChangeEvent e) {
        // only output when value is set (when the mouse is released from the knob)
        // remove this if statement if you would like output whenever the knob is moved
        if(!slider.getValueIsAdjusting()) {
            System.out.println(slider.getValue());
        }
    }

});    

有关 JSlider 的更多信息和官方教程，请查看 The Java™ Tutorials - How to Use Sliders