为JTree句柄添加鼠标悬停效果

Question

我正在尝试在 JTree 的 Collapsed Icon 上制作自定义的鼠标悬停效果。但是，我不确定如何仅针对单个句柄进行操作，而不是所有句柄。

如果您运行下面的代码，您将看到当您将鼠标悬停在 JTree 的任何句柄、节点或叶子上时，所有折叠的句柄都会更改为悬停状态。这不是期望的结果。那么，当我悬停在一个句柄上时，如何只更改一个句柄，并且最好不要在其旁边的节点上悬停时更改？

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;
import javax.swing.tree.*;
import javax.swing.plaf.basic.*;

@SuppressWarnings("serial")
public class DirectoryExplorer extends JFrame {
    private DirectoryExplorer() {
        super("Directory Explorer");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new GridLayout(1, 1));
        createPanel();
        setSize(800,600);
        setVisible(true);
    }

    private void createPanel() {
        JPanel panel = new JPanel(new GridLayout(1, 1));

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Hello");
        root.add(new DefaultMutableTreeNode("1"));
        root.add(new DefaultMutableTreeNode("2"));
        root.add(new DefaultMutableTreeNode("3"));

        JTree tree = new JTree();
        BasicTreeUI tUI = (BasicTreeUI) tree.getUI();
        tUI.setCollapsedIcon(new ImageIcon("resources/closed.png"));
        tUI.setExpandedIcon(new ImageIcon("resources/open.png"));
        tree.setShowsRootHandles(true);
        tree.addMouseMotionListener(new MouseHandler(tree));

        panel.add(new JScrollPane(tree));
        getContentPane().add(panel);
    }

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

    private class MouseHandler implements MouseMotionListener {
        JTree t = null;
        BasicTreeUI tUI = null;

        public MouseHandler(JTree tree) {
            t = tree;
            tUI = (BasicTreeUI) tree.getUI();
        }

        @Override
        public void mouseDragged(MouseEvent e) {

        }

        @Override
        public void mouseMoved(MouseEvent e) {
            TreePath selPath = t.getPathForLocation(e.getX(), e.getY());
            if(selPath != null) 
                tUI.setCollapsedIcon(new ImageIcon("resources/rollover.png"));
            else
                tUI.setCollapsedIcon(new ImageIcon("resources/closed.png"));
            t.repaint();
        }
    }
}

- Dan

---

“你知道当鼠标悬停在它们上面时，是否可以针对单个句柄进行定位吗？”我从未尝试过。 - trashgod

猜测您需要子类化“BasicTreeUI”。 - trashgod

@trashgod 你是对的。我通过创建 BasicTreeUI 的子类来实现了它，如果你有兴趣的话，下面是代码： - Dan

Answer 1

为了实现期望的结果，您需要覆盖 BasicTreeUI.paintExpandControl() 和 BasicTreeUI.MouseHandler.mouseMoved()。您还需要创建一些方法，如 setRolloverIcon()。

一个可行的示例可能是这样的：

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.net.MalformedURLException;
import java.net.URL;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.plaf.basic.BasicTreeUI;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;

@SuppressWarnings("serial")
public class DirectoryExplorer extends JFrame {
    private DirectoryExplorer() {
        super("Directory Explorer");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new GridLayout(1, 1));
        createPanel();
        setSize(800,600);
        setVisible(true);
    }

    private void createPanel() {
        JPanel panel = new JPanel(new GridLayout(1, 1));

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Hello");
        root.add(new DefaultMutableTreeNode("1"));
        root.add(new DefaultMutableTreeNode("2"));
        root.add(new DefaultMutableTreeNode("3"));

        JTree tree = new JTree();

        //UI Stuff//
        TreeHandleUI tUI = new TreeHandleUI(tree);
        tree.setUI(tUI);
        try {
            tUI.setCollapsedIcon(new ImageIcon(new URL("https://istack.dev59.com/nKJFv.webp")));
            tUI.setExpandedIcon(new ImageIcon(new URL("https://istack.dev59.com/NJvcp.webp")));
            tUI.setRolloverIcon(new ImageIcon(new URL("https://istack.dev59.com/jN6uX.webp")));
        } catch(MalformedURLException e) {
            System.out.println("Bad URL / URLs");
        }
        ////////////

        tree.setShowsRootHandles(true);

        panel.add(new JScrollPane(tree));
        getContentPane().add(panel);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new DirectoryExplorer());
    }

    private class TreeHandleUI extends BasicTreeUI {
        ///Variables
        private JTree t = null;
        private Icon rolloverIcon = null;
        private boolean rolloverEnabled = false;
        private UpdateHandler uH = null;

        private boolean isLeftToRight( Component c ) {
            return c.getComponentOrientation().isLeftToRight();
        }

        public TreeHandleUI(JTree tree) {
            t = tree;
            uH = new UpdateHandler(t);
            t.addMouseMotionListener(uH);
        }

        public void setRolloverIcon(Icon rolloverG) {
            Icon oldValue = rolloverIcon;
            rolloverIcon = rolloverG;
            setRolloverEnabled(true);
            if (rolloverIcon != oldValue) {
                t.repaint();
            }
        }

        private void setRolloverEnabled(boolean handleRolloverEnabled) {
            boolean oldValue = rolloverEnabled;
            rolloverEnabled = handleRolloverEnabled;
            if (handleRolloverEnabled != oldValue) {
                t.repaint();
            }
        }

        @Override
        protected void paintExpandControl(Graphics g,
                                          Rectangle clipBounds, Insets insets,
                                          Rectangle bounds, TreePath path,
                                          int row, boolean isExpanded,
                                          boolean hasBeenExpanded,
                                          boolean isLeaf) {
            Object value = path.getLastPathComponent();

            if (!isLeaf && (!hasBeenExpanded || treeModel.getChildCount(value) > 0)) {
                int middleXOfKnob;
                if (isLeftToRight(t)) {
                    middleXOfKnob = bounds.x - getRightChildIndent() + 1;
                } else {
                    middleXOfKnob = bounds.x + bounds.width + getRightChildIndent() - 1;
                }
                int middleYOfKnob = bounds.y + (bounds.height / 2);

                if (isExpanded) {
                    Icon expandedIcon = getExpandedIcon();
                    if(expandedIcon != null)
                      drawCentered(tree, g, expandedIcon, middleXOfKnob, middleYOfKnob );
                } else if(isLocationInExpandControl(path, uH.getXPos(), uH.getYPos()) && !isExpanded && rolloverEnabled) {
                    if(row == uH.getRow()) {
                        if(rolloverIcon != null)
                            drawCentered(tree, g, rolloverIcon, middleXOfKnob, middleYOfKnob);
                    } else {
                        Icon collapsedIcon = getCollapsedIcon();
                        if(collapsedIcon != null)
                          drawCentered(tree, g, collapsedIcon, middleXOfKnob, middleYOfKnob);
                    }
                } else {
                    Icon collapsedIcon = getCollapsedIcon();
                    if(collapsedIcon != null)
                      drawCentered(tree, g, collapsedIcon, middleXOfKnob, middleYOfKnob);
                }
            }
        }

        private class UpdateHandler extends BasicTreeUI.MouseHandler {
            private JTree t = null;
            private int xPos = 0;
            private int yPos = 0;

            private boolean leftToRight(Component c) {
                return c.getComponentOrientation().isLeftToRight();
            }

            public UpdateHandler(JTree tree) {
                t = tree;
            }

            @Override
            public void mouseMoved(MouseEvent e) {
                xPos = e.getX();
                yPos = e.getY();
                t.repaint();
            }

            public int getXPos() {
                return xPos;
            }

            public int getYPos() {
                return yPos;
            }

            public int getRow() {
                return getRowForPath(t, getClosestPathForLocation(t, xPos, yPos));
            }
        }
    }
}

代码会在没有下载图片的情况下运行，但这些图片仍然可以从以下链接中获取

closed.png

open.png

rollover.png

- Dan

---

@trashgod 好的，谢谢。我更新了我的答案，包括 EventQueue.invokeLater(() -> new DirectoryExplorer());。 - Dan

@trashgod，如果您有时间，能否告诉我您对这段代码的想法？ - Dan