使用 LAF Nimbus 在 Java Native Classes、SynthTreeUI 中发现 NullPointerException 的原因

Question

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审稿人注意：这可能是 NimbusLookAndFeel 中的一个（可能已知的）错误，并且（目前）还不是规范 NPE 问题的副本。 p>

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我有多个类，但我不知道异常可能暗示其中的哪一个。

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.plaf.synth.SynthTreeUI.paint(SynthTreeUI.java:382)
        at javax.swing.plaf.synth.SynthTreeUI.update(SynthTreeUI.java:269)
        at javax.swing.JComponent.paintComponent(JComponent.java:780)
        at javax.swing.JComponent.paint(JComponent.java:1056)
        at javax.swing.JComponent.paintToOffscreen(JComponent.java:5210)
        at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1579)
        at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1502)
        at javax.swing.RepaintManager.paint(RepaintManager.java:1272)
        at javax.swing.JComponent._paintImmediately(JComponent.java:5158)
        at javax.swing.JComponent.paintImmediately(JComponent.java:4969)
        at javax.swing.RepaintManager$4.run(RepaintManager.java:831)
        at javax.swing.RepaintManager$4.run(RepaintManager.java:814)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)
        at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)
        at javax.swing.RepaintManager.access$1200(RepaintManager.java:64)
        at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
        at java.awt.EventQueue.access$500(EventQueue.java:97)
        at java.awt.EventQueue$3.run(EventQueue.java:709)
        at java.awt.EventQueue$3.run(EventQueue.java:703)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

如您所见，异常没有将我的代码链接到任何地方。

对于create a Minimal, Complete, and Verifiable example 我无法通过所有项目，因为它很长，我无法在上面放一段代码，因为我没有找到源头的线索。

我扩展：

1. 来自DefaultMutableTreeNode为了

   @Override public String toString()
   

2. 来自DefaultTreeCellRenderer为了

   @Override public Component getTreeCellRendererComponent(JTree tree, 
       Object value, boolean selected, boolean expanded, boolean leaf, 
       int row, boolean hasFocus)
   

现在的情况是：

//Fails
//javax.swing.UIManager.setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");

//Works
//javax.swing.UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");

//Works
//javax.swing.UIManager.setLookAndFeel("com.apple.laf.AquaLookAndFeel");

注意： 我不需要解决方案。如果不提供代码，那将是不合逻辑的！！！

问题： 我应该具体在哪里寻找问题的根源？

Answer 1

我的 JTree 也有类似的情况，我的问题的原因是（在 Thread 中更新 JTree），拯救是使用 SwingWorker。 解释基于与

类似的帖子

https://www.javacodegeeks.com/2012/12/multi-threading-in-java-swing-with-swingworker.html

我不假装给出一个严格的功能解决方案或代码，我只是给你一个如何解决问题的想法。

class SwingWorkerCustomDTO extends SwingWorker<Void, CustomDTO> {

    @Override
    protected Void doInBackground() throws Exception {
        //Initialization and Iterative Operation over JTree
        myJTree = new JTree(/**/); // or Set the Model

        //someLongTask(arguments);
        /*long time/delayed Task that he sometimes performs o operations on JTree.*/

        return null;
    }

    @Override
    protected void done() {
        //reload or update JTree /*or what you imagine doing*/
        //removeOrUpdateTask();

        //example
        DefaultTreeModel treeModel = ((DefaultTreeModel)myJTree.getModel());
        DefaultMutableTreeNode rootTreeNode = (DefaultMutableTreeNode) treeModel.getRoot();
        treeModel.reload(rootTreeNode);
    }

    @Override
    protected void process(List<CustomDTO> chunks) {
        for (final CustomDTO chunk : chunks) {
            //The Operation (Add/Remove/Update) of JTree are performed here!.
            switch (chunk.getOperarionType()) {
              case ADD_CONSTANT:  /*or what you define*/
                //Add Node(Object or Objects[]) to Some JTree;
                break;
              case UPDATE_CONSTANT:  /*or what you define*/
                //Update Node(Object or Objects[]) to Some JTree;
                break;
              case REMOVE_CONSTANT:
                //Remove Node(Object or Objects[]) from Some JTree;
                break;
            }
        }
    }

    public void callPublish(CustomDTO customDTO) {
        /*I expose a public method to pass arguments that make functionalities
        (Add/Remove/Update Node) required in the JTree invoked externally.*/
        publish(customDTO);
    }

}

你可以在外部调用你自己的自定义类

swingWorkerCustomDTO.callPublish(
    new CustomDTO(int OperationType/*or what you define*/,
        Object argument /*or Object[] arguments*/));

CustomDTO是你定义的一个类，其中包含操作（你想做什么），比如int属性，还需要另外一个属性。