如何为JTree单元设置透明背景？ [英] How to set transparent background for JTree cell?

问题描述

伙计，

我正在尝试创建渐变JTree控件。除了树单元格的背景不透明外，以下代码大部分都有效。如果有人打电话告诉我，我做得不对，我将不胜感激。

I am trying to create a gradient JTree control. The following code mostly works except that the background for the tree cell is not transparent. I would appreciate it if someone call tell me what is it that I am not doing right.

提前感谢您的帮助。

问候，

Peter

Regards,
Peter

package TestPackage;

import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
import java.awt.*;

public class Test {

    public Test() {
        JFrame frame = new JFrame();

        JPanel framePanel = new JPanel();
        framePanel.setLayout(new BorderLayout());
        frame.setContentPane(framePanel);


        DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Item");
        DefaultMutableTreeNode childNode = new DefaultMutableTreeNode("Child");
        rootNode.add(childNode);

        GradientTree tree = new GradientTree(rootNode);
        // JTree tree = new JTree(rootNode);
        // tree.setBackground(Color.blue);
        tree.setCellRenderer(new MyRenderer());

        JScrollPane scroll = new JScrollPane(tree);
        scroll.setOpaque(false);
        framePanel.add(scroll, BorderLayout.CENTER);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Test();
            }
        });
    }


    @SuppressWarnings("serial")
    public static class GradientTree extends JTree {

        public GradientTree(DefaultMutableTreeNode node) {
            super(node);
        }


        @Override
        protected void paintComponent(Graphics g) {

            int h = getHeight();
            int w = getWidth();

            GradientPaint gradientPaint = new GradientPaint(0, 0, Color.LIGHT_GRAY, 0, h, Color.WHITE);

            Graphics2D g2D = (Graphics2D) g;
            g2D.setPaint(gradientPaint);
            g2D.fillRect(0, 0, w, h);

            this.setOpaque(false);
            super.paintComponent(g);
            this.setOpaque(true);
        }
    }

    @SuppressWarnings({"serial" })
    private class MyRenderer extends DefaultTreeCellRenderer {
        public MyRenderer() {
            this.setOpaque(false);
            this.setForeground(Color.RED);
        }

        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);

            return this;
        }
    }
}

推荐答案

这是一个真正的痛苦。 DefaultTreeCellRenderer 将忽略 opaque 值并无论如何填充其内容。但是，你可以尝试一个标志。我以前做过，但没有时间测试它...

This is a real pain. The DefaultTreeCellRenderer will ignore the opaque value and fill it's contents anyway. However, there is a flag you can try. I've done it in the past, but don't have time to test it...

尝试 UIManager.put（树。 rendererFillBackground，false）。尝试在任何渲染器之前执行此操作，但在应用任何外观设置之后。

Try UIManager.put("Tree.rendererFillBackground", false). Try and do this before anything is renderer, but after any look and feel settings have been applied.

更新

在创建任何树之前设置此属性非常重要

It is very important to set this property BEFORE you create any trees

随... ...

< img src =https://i.stack.imgur.com/D51Cb.pngalt =在此处输入图像说明>

public class TestTreeRenderer {

    public static void main(String[] args) {
        new TestTreeRenderer();
    }

    public TestTreeRenderer() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TreePane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class TreePane extends JPanel {

        private JTree tree;

        public TreePane() {
            // THIS IS VERY IMPORTANT
            // You must set this BEFORE creating ANY trees!!
            UIManager.put("Tree.rendererFillBackground", false);

            setLayout(new BorderLayout());
            tree = new JTree();
            tree.setBackground(Color.BLUE);

            System.out.println("Loading files...");
            File root = new File("/etc");
            DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode(root.getName());
            for (File file : root.listFiles()) {
                rootNode.add(new DefaultMutableTreeNode(file.getName()));
            }
            System.out.println("Loading model");
            DefaultTreeModel model = new DefaultTreeModel(rootNode);
            tree.setModel(model);

            add(new JScrollPane(tree));
        }
    }
}

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