jSlider去點擊的位置 - 只有在Macintosh上的問題

Question

我一直在使用上述MetalSliderUI解決方案爲我所有的JSliders。 Windows用戶對此感到滿意。我讚賞stackoverflow.com找到這個解決方案 在這裏討論的解決方法： JSlider question: Position after leftclick

現在最近一個MAC OSX/64位用戶試圖使用我的軟件，他得到來自MetalSliderUI引用空指針異常。代碼

樣品，我加入到JFrame中的構造函數：

// 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); 
        } 
       } 
      ); 

異常不引述確切線在我的代碼：

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) 

你有什麼建議解決這個問題，其只在Mac上出現？

霍華德

Answer 1

這是很難沒有SSCCE說（更難沒有Mac電腦。來測試），但這些問題往往是由於沒有更新的EDT的GUI引起的。有關更多詳細信息，請參閱Java教程的Concurrency in Swing課程。

Answer 2

問題出現在MetalSliderUI的第92行，它需要UI默認值Slider.trackWidth等等。該值不會出現在com.apple.laf.AquaSliderUI中。

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

一個簡單的選擇是使用BasicSliderUI。更復雜的方法是初始化MetalLookAndFeel並保存對您的子類的引用以備後用。

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