排序JTable会导致NullPointerException

问题描述

我有一个JTable，单击适当的按钮后，该表开始填充在后台进行的文件树遍历的结果.效果很好.

I have a JTable which, when the appropriate button is clicked, begins to fill with the results of a file tree walk that goes on in the background. This works fine.

然后我决定要对表格进行排序.经过一番阅读后，我创建了一个TableRowSorter并将表设置为使用它.它似乎可以正常工作，但是在仔细检查后，我发现缺少几个文件结果.我禁用了分类器，然后再次运行程序，所有文件都存在，再次启用分类器后，一些文件丢失了，但每次删除文件似乎都是不同的文件.

I then decided I want the table to be sorted. After some reading I created a TableRowSorter and set the table to use it. It appeared to work, but upon closer inspection I noticed several of the file results were absent. I disabled the sorter and ran the program again and all of the files were present, upon re-enabling the sorter again some were missed, but it seemed to be different files each time that were being dropped.

为了检验这一点，我创建了一个自包含的代码块作为测试(请参见下文)，该代码块代表JTable代码(实际上，大块代码是直接从现有程序代码中提取的).文件树遍历由for循环表示.同样，它无需分选器也可以完美工作.但是，当我启用排序器时(通过第29行取消注释)，整个程序冻结了，并被告知存在NullPointerException.

To examine this I created a self-contained block of code as a test (see below), which was to be representative of the JTable code (In fact, large chunks were lifted directly from the existing program code). The file tree walk is represented by a for loop. Again, it worked perfectly without the sorter. When I enabled the sorter, however, (by uncommenting line 29) the entire program frozeand I was told there was a NullPointerException.

我不知道是什么原因导致了这些问题，或者实际上是否与之相关.任何关于出什么问题的想法都欢迎.

I have no Idea what is causing either of these problems, nor if they are, in fact, even related. Any ideas on what is wrong are welcome.

import javax.swing.table.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class Sort extends JFrame{

    private JTable table;
    private DefaultTableModel model;
    private TableRowSorter<DefaultTableModel> sorter;

    private JButton go;

    public Sort(){
        super("Sort");

        // Create table and model
        model = new DefaultTableModel(0, 4);
        table = new JTable(model);

        // Setup sorting
        sorter = new TableRowSorter<DefaultTableModel>(model);
        ArrayList<RowSorter.SortKey> sortKeys = new ArrayList<RowSorter.SortKey>();
        sortKeys.add(new RowSorter.SortKey(2, SortOrder.ASCENDING));
        sortKeys.add(new RowSorter.SortKey(3, SortOrder.ASCENDING));
        sortKeys.add(new RowSorter.SortKey(0, SortOrder.ASCENDING));
        sorter.setSortKeys(sortKeys);
        //table.setRowSorter(sorter);

        // Create Scroll Pane
        JScrollPane tableScroller = new JScrollPane(table);
        table.setFillsViewportHeight(true);
        tableScroller.setPreferredSize(new Dimension(500, 200));

        // Setup button
        go = new JButton("Go");
        go.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>(){
                    public Void doInBackground(){
                        for(int i = 0; i < 200; i++){
                            model.addRow( new Object[] { (new Integer(i)), String.valueOf(i), String.valueOf(i%50), String.valueOf(i%10) } );
                        }
                        return null;
                    }
                };
                worker.execute();
            }
        });

        // Assemble GUI
        JPanel panel = new JPanel(new BorderLayout());
        panel.add(tableScroller, BorderLayout.CENTER);
        panel.add(go, BorderLayout.SOUTH);

        setContentPane(panel);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        pack();
        setVisible(true);

    }

    public static void main(String[] args){
        SwingUtilities.invokeLater(new Runnable(){
            public void run(){
                new Sort();
            }
        });
    }

}

Stacktrace

这是堆栈跟踪的一部分，它会重复..

Stacktrace

This is part of the stack trace, it repeats..

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.DefaultRowSorter.convertRowIndexToModel(DefaultRowSorter.java:518)
    at javax.swing.JTable.convertRowIndexToModel(JTable.java:2645)
    at javax.swing.JTable.getValueAt(JTable.java:2720)
    at javax.swing.JTable.prepareRenderer(JTable.java:5718)
    at javax.swing.plaf.basic.BasicTableUI.paintCell(BasicTableUI.java:2114)
    at javax.swing.plaf.basic.BasicTableUI.paintCells(BasicTableUI.java:2016)
    at javax.swing.plaf.basic.BasicTableUI.paint(BasicTableUI.java:1812)
    at javax.swing.plaf.ComponentUI.update(ComponentUI.java:161)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
    at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
    at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
    at java.awt.EventQueue.access$000(EventQueue.java:101)
    at java.awt.EventQueue$3.run(EventQueue.java:666)
    at java.awt.EventQueue$3.run(EventQueue.java:664)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    ...

推荐答案

您的代码有一个大问题，可能解释您观察到的内容:您正在外部修改表模型> EDT，这是邪恶的.

Your code has a big problem that may explain what you observe: you are modifying your table model outside the EDT, which is evil.

由于您使用的是SwingWorker，因此应尝试完全正确使用它，例如使用其publish API调用model.addRow().

Since you are using a SwingWorker, you should try to use it completely correctly, e.g. use its publish API to call model.addRow().

这篇关于排序JTable会导致NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！