扩展节点时，包含 HTML 代码的 JLabel 节点的 JTree 引发异常答案

【问题标题】：JTree with JLabel nodes containing HTML code throws exception when expanding nodes扩展节点时，包含 HTML 代码的 JLabel 节点的 JTree 引发异常
【发布时间】：2014-01-29 12:30:02
【问题描述】：

我创建了一个以 JLabels 作为对象的 JTree。包含 HTML 的 JLabel。例如：

new JLabel("<html><FONT COLOR=ORANGE size=\"2\"><B>Unknown Http Response Status</B></FONT></html>")

我使用了这个 Cell 渲染器：

public class TreeWithJLabelCellRenderer extends DefaultTreeCellRenderer {
    private JLabel label;

    public TreeWithJLabelCellRenderer() {
        label = new JLabel();
    }

    public Component getTreeCellRendererComponent(JTree tree,
                                                  Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) {
        Object nodeValue = ((DefaultMutableTreeNode) value).getUserObject();

        label=(JLabel)nodeValue;

        return label;
    }
}

我的问题 - 当包含 JTree 的 JFrame 出现并且我尝试展开树节点时，我得到了这个异常：

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.JLabel cannot be cast to javax.swing.text.JTextComponent
    at javax.swing.text.html.EditableView.paint(EditableView.java:76)
    at javax.swing.text.BoxView.paintChild(BoxView.java:161)
    at javax.swing.text.BoxView.paint(BoxView.java:433)
    at javax.swing.text.BoxView.paintChild(BoxView.java:161)
    at javax.swing.text.BoxView.paint(BoxView.java:433)
    at javax.swing.text.ParagraphView.paint(ParagraphView.java:587)
    at javax.swing.text.html.ParagraphView.paint(ParagraphView.java:233)
    at javax.swing.text.BoxView.paintChild(BoxView.java:161)
    at javax.swing.text.BoxView.paint(BoxView.java:433)
    at javax.swing.text.html.BlockView.paint(BlockView.java:282)
    at javax.swing.text.BoxView.paintChild(BoxView.java:161)
    at javax.swing.text.BoxView.paint(BoxView.java:433)
    at javax.swing.text.html.BlockView.paint(BlockView.java:282)
    at javax.swing.plaf.basic.BasicHTML$Renderer.paint(BasicHTML.java:481)
    at com.seaglasslookandfeel.util.SeaGlassGraphicsUtils.paintText(SeaGlassGraphicsUtils.java:162)
    at com.seaglasslookandfeel.ui.SeaGlassLabelUI.paint(SeaGlassLabelUI.java:163)
    at com.seaglasslookandfeel.ui.SeaGlassLabelUI.update(SeaGlassLabelUI.java:146)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.CellRendererPane.paintComponent(CellRendererPane.java:151)
    at javax.swing.plaf.basic.BasicTreeUI.paintRow(BasicTreeUI.java:1539)
    at gui.HttpRequesterTool.TreeWithJLabelUI.paintRow(TreeWithJLabelUI.java:18)
    at javax.swing.plaf.basic.BasicTreeUI.paint(BasicTreeUI.java:1223)
    at javax.swing.plaf.ComponentUI.update(ComponentUI.java:161)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JViewport.paint(JViewport.java:731)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JLayeredPane.paint(JLayeredPane.java:585)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1529)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1452)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1249)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5167)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4978)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:808)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

我做错了什么？

【问题讨论】：

标签： java swing exception jlabel jtree

【解决方案1】：

你得到一个ClassCastException，因为getUserObject()最初会返回一个String，它不能转换为JLabel。

您可以使用setText(...) 替换文本。像这样的

DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
String text = ((String) node.getUserObject());
String newText = "<html><FONT COLOR=ORANGE size=\\\"2\\\"><B>" + text + "</B></FONT></html>";
setText(newText);

return this;

import java.awt.Component;
import javax.swing.JFrame;
import javax.swing.JTree;
import javax.swing.SwingUtilities;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;

public class TreeCellRender {

    JTree tree = new JTree();

    public TreeCellRender() {
        DefaultTreeCellRenderer renderer = new DefaultTreeCellRenderer() {
            @Override
            public Component getTreeCellRendererComponent(JTree tree,
                    Object value, boolean sel, boolean expanded, boolean leaf,
                    int row, boolean hasFocus) {
                super.getTreeCellRendererComponent(tree, value, sel, expanded,
                        leaf, row, hasFocus);

                DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
                String text = ((String) node.getUserObject());
                String newText = "<html><FONT COLOR=ORANGE size=\\\"2\\\"><B>" + text + "</B></FONT></html>";
                setText(newText);
                return this;
            }
        };

        tree.setCellRenderer(renderer);

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(tree);
        frame.pack();
        frame.setVisible(true);
    }

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

另外，如果您只想设置字体和颜色，您可以轻松地在您的方法中完成此操作

public Component getTreeCellRendererComponent(....) {
    ....
    setFont(new Font("impact", Font.PLAIN, 20));
    setForeground(Color.GREEN);
    return this;
}

更新

原发帖人提出的另一种方式是这样的

另一种方法：使用包含 html 代码的字符串节点创建树。渲染器将是这样的：

public class MyTreeCellRenderer extends DefaultTreeCellRenderer {
    DefaultTreeCellRenderer defaultTreeCellRenderer=new DefaultTreeCellRenderer();

    @Override
    public Component getTreeCellRendererComponent(JTree tree,Object value, boolean sel, boolean expanded, boolean leaf,int row, boolean hasFocus) {
        super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus);

        DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
        String text = (String)node.getUserObject();
        JTextPane textPane = new JTextPane();
        textPane.setContentType("text/html");
        textPane.setText(text);
        return textPane;
    }
}

【讨论】：

感谢您的回答。我认为这几乎对我有帮助，因为我将 JLabel 对象作为节点，所以 getUserObject() 确实返回了我的 JLabel。问题是例外......有什么想法吗？
我不能告诉你。 ClassCastException 来自您尝试将JLabel 转换为nodeValue 的行。我唯一怀疑的是我之前在回答中提到的内容。
我建议你做的是放一个if (nodeValue instanceof String) { System.out.println(nodeValue); } 看看它是否是一个字符串。并注释掉您投射 JLabel 的代码
我现在更改了所有代码 - 而不是 JLabel 我发送一个“HTML”字符串。现在我得到一个新的异常（我使用的是单元格渲染器代码）： java.lang.ClassCastException: javax.swing.plaf.synth.SynthTreeUI$SynthTreeCellRenderer cannot be cast to javax.swing.text.JTextComponent
好的！我修好了它！！我更改了渲染器以获取文本（如您所建议的），然后创建了一个要显示的 JTextPane。工作:-) 10 倍！