如何在不调度change事件的情况下更新JSlider的最大值

时间:2013-04-24 14:00:45

标签: java swing jslider

我有一些更新JSlider的代码;在另一个时间点,JSlider的最大值需要更新。问题是当我在滑块上调用setMaximum()时,它还会调度ChangeEvent。为了避免我这样做:

slider.removeChangeListener(this);
slider.setMaximum(newMax);
slider.addChangeListener(this);

是否有更干净/更优雅的方式?

4 个答案:

答案 0 :(得分:3)

一种干净的方式可能(取决于你真正需要的东西)来实现一个自定义的BoundedRangeModel,它可以触发一个可以携带实际更改的属性的自定义ChangeEvent:

/**
 * Extended model that passes the list of actually changed properties
 * in an extended changeEvent.
 */
public static class MyBoundedRangeModel extends DefaultBoundedRangeModel {

    public MyBoundedRangeModel() {
    }

    public MyBoundedRangeModel(int value, int extent, int min, int max) {
        super(value, extent, min, max);
    }

    @Override
    public void setRangeProperties(int newValue, int newExtent, int newMin,
            int newMax, boolean adjusting) {
        int oldMax = getMaximum();
        int oldMin = getMinimum();
        int oldValue = getValue();
        int oldExtent = getExtent();
        boolean oldAdjusting = getValueIsAdjusting();
        // todo: enforce constraints of new values for all
        List<String> changedProperties = new ArrayList<>();
        if (oldMax != newMax) {
           changedProperties.add("maximum"); 
        }
        if (oldValue != newValue) {
            changedProperties.add("value");
        }
        // todo: check and add other properties 
        changeEvent = changedProperties.size() > 0 ? 
                new MyChangeEvent(this, changedProperties) : null;
        super.setRangeProperties(newValue, newExtent, newMin, newMax, adjusting);
    }


}

/**
 * Extended ChangeEvent that provides a list of actually 
 * changed properties. 
 */
public static class MyChangeEvent extends ChangeEvent {

    private List<String> changedProperties;

    /**
     * @param source
     */
    public MyChangeEvent(Object source, List<String> changedProperties) {
        super(source);
        this.changedProperties = changedProperties;
    }

    public List<String> getChangedProperties() {
        return changedProperties;
    }

}

它的用法类似于:

final JSlider slider = new JSlider();
slider.setModel(new MyBoundedRangeModel(0, 0, -100, 100));
ChangeListener l = new ChangeListener() {

    @Override
    public void stateChanged(ChangeEvent e) {
        if (e instanceof MyChangeEvent) {
            MyChangeEvent me = (MyChangeEvent) e;
            if (me.getChangedProperties().contains("value")) {
               System.out.println("new value: " + 
                    ((BoundedRangeModel) e.getSource()).getValue()); 
            }
            if (me.getChangedProperties().contains("maximum")) {
                System.out.println("new max: " + 
                    ((BoundedRangeModel) e.getSource()).getMaximum()); 
            }
        } else {
            // do something else or nothing
        }
    }
};
slider.getModel().addChangeListener(l);

请注意,您必须使用模型注册侦听器,而不是使用滑块(原因是滑块创建普通类型的新changeEvent)

答案 1 :(得分:0)

您可以检查是谁在听众中触发了更改。它仍然非常脏,但您不必删除更改侦听器。

答案 2 :(得分:0)

它看起来像问题一样,实质上是this question.在这种情况下,我担心答案是“不”

答案 3 :(得分:0)

如果您只需要滑块在值更改时触发事件,您可以通过以下方式简化kleopatra的答案:

// make sure slider only fires changEvents when value changes
slider.setModel(new DefaultBoundedRangeModel() {
        final ChangeEvent theOne=new ChangeEvent(this);         
        @Override
        public void setRangeProperties(int newValue, int newExtent, int newMin,int newMax, boolean adjusting) 
            changeEvent= (getValue() != newValue ? theOne:null);
            super.setRangeProperties(newValue, newExtent, newMin, newMax, adjusting);
        }
        @Override
        protected void fireStateChanged()
        {
            if(changeEvent==null) return;
            super.fireStateChanged();
        }
    });

然后你需要做的就是在模型上注册一个“标准”ChangeListener,它只会在值发生变化时被调用,而不是在最大或最小变化时被调用。

slider.getModel().addChangeListener(new ChangeListener() {
    public void stateChanged(ChangeEvent e) { 
        // do something here when value changes 
    });

});