Question

我一直在为所有JSliders使用上面的MetalSliderUI解决方案。 Windows用户对此很满意。我很高兴在stackoverflow.com上找到这个解决方案这里讨论了解决方案： JSlider question: Position after leftclick

最近，MAC OSX / 64位用户正在尝试使用我的软件，他从MetalSliderUI引用中获取空指针异常。

我添加到JFrame构造函数的代码示例：

// Radio Window Elecraft K3 RFPWR Slider - when click on slider
            // go to the value instead of going up/down one tick.
            jSliderElecraftK3RFPWR.setUI(
                new MetalSliderUI() {
                    protected void scrollDueToClickInTrack(int direction) {
                        int value = jSliderElecraftK3RFPWR.getValue();
                        if (jSliderElecraftK3RFPWR.getOrientation() == JSlider.HORIZONTAL) {
                            value = this.valueForXPosition(jSliderElecraftK3RFPWR.getMousePosition().x);
                        } else if (jSliderElecraftK3RFPWR.getOrientation() == JSlider.VERTICAL) {
                            value = this.valueForYPosition(jSliderElecraftK3RFPWR.getMousePosition().y);
                        }
                        jSliderElecraftK3RFPWR.setValue(value);
                    }
                }
            );

在我的代码中没有引用确切行的异常：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at 
javax.swing.plaf.metal.MetalSliderUI.installUI(MetalSliderUI.java:92) at 
javax.swing.JComponent.setUI(JComponent.java:662) at 
javax.swing.JSlider.setUI(JSlider.java:300) at 
HamRadioIntegrator_N3ZH.JFrameRadio.(JFrameRadio.java) at 
HamRadioIntegrator_N3ZH.JFrameRadio$550.run(JFrameRadio.java) at
java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) at 
java.awt.EventQueue.dispatchEventImpl(EventQueue.java:678) at 
java.awt.EventQueue.access$000(EventQueue.java:86) at 
java.awt.EventQueue$1.run(EventQueue.java:639) at 
java.awt.EventQueue$1.run(EventQueue.java:637) at 
java.security.AccessController.doPrivileged(Native Method) at 
java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87) 
at java.awt.EventQueue.dispatchEvent(EventQueue.java:648) at 
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296) at 
java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211) at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201) at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196) at 
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188) at  
java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

您是否有任何解决此问题的建议仅在Mac上发生？

霍华德

Answer 1

很难说没有SSCCE（没有Mac就更难以测试），但这些问题通常是由于未能在EDT上更新GUI而引起的。有关详细信息，请参阅Java教程的Concurrency in Swing课程。

Answer 2

问题出在MetalSliderUI的第92行，其中包含名为Slider.trackWidth的UI默认值等。该值未显示在com.apple.laf.AquaSliderUI中。

trackWidth = ((Integer)UIManager.get("Slider.trackWidth")).intValue();

一个简单的替代方法是使用BasicSliderUI。更复杂的方法是初始化MetalLookAndFeel并保存对子类的引用以供以后使用。

LookAndFeel save = UIManager.getLookAndFeel();
LookAndFeel laf = new MetalLookAndFeel();
UIManager.setLookAndFeel(laf);
SliderUI mySliderUI = new MetalSliderUI() { ... };
UIManager.setLookAndFeel(save);

jSlider转到单击位置 - 仅在Macintosh上出现问题

2 个答案: