Java 仅在鼠标悬停时更改字母的颜色

我有一个Jframe，有两个按钮：“a”和“B”。单击按钮“A”应在JPanel中显示大写字母A。仅在鼠标悬停时，画布中的任何“A”字母都应显示为红色。当鼠标离开时，文本颜色应恢复为黑色

我已经为此编写了代码，它只工作一次。字母“A”变为红色，但不会变回黑色。此外，它不适用于多个“A”

JFrame的代码：

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class DrawFrame extends JFrame{
    private final int WIDTH = 500;
    private final int HEIGHT = 300;

    private GUIModel model;

    private JButton number1;
    private JButton number2;

    private JPanel numberPanel;
    private DrawPanel graphicsPanel;

    public DrawFrame()
    {
        this.model = new GUIModel(" ");

        createSelectionPanel();
        createGraphicsPanel();

        this.setSize(WIDTH, HEIGHT);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    private void createSelectionPanel()
    {
        numberPanel = new JPanel();

        ButtonListener listener = new ButtonListener();

        number1 = new JButton("A");
        number1.addActionListener(listener);

        number2 = new JButton("B");
        number2.addActionListener(listener);  

        numberPanel.setLayout(new GridLayout(2,2));
        numberPanel.add(number1);
        numberPanel.add(number2);

        this.add(numberPanel, BorderLayout.WEST);
    }

    private void createGraphicsPanel()
    {
        //instantiate drawing panel
        graphicsPanel = new DrawPanel(WIDTH, HEIGHT, model);
        //add drawing panel to right
        add(graphicsPanel);
    }

    private class ButtonListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent event) {
            model.setDisplayString(event.getActionCommand());
        }
    }

    //creates a drawing frame
    public static void main(String[] args)
    {
        DrawFrame draw = new DrawFrame();
    }   
}

JPanel的代码：

import javax.swing.JPanel;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import java.util.List;

public class DrawPanel extends JPanel{
    private static final long serialVersionUID = 3443814601865936618L;

    private Font font = new Font("Default", Font.BOLD, 30);

    private static final Color DEFAULT_TEXT_COLOR = Color.BLACK;
    private static final Color HOVER_TEXT_COLOR = Color.RED;
    private Color color = DEFAULT_TEXT_COLOR;

    private List<GUIModel> numberList = new ArrayList<GUIModel>();
    private GUIModel model;
    boolean mouseHover = false;

    public DrawPanel(int width, int height, GUIModel model){
        this.setPreferredSize(new Dimension(width, height));
        this.model = model;

        //set white background for drawing panel
        setBackground(Color.WHITE);

        //add mouse listeners
        MouseHandler mouseHandler = new MouseHandler();
        this.addMouseListener(mouseHandler);
        this.addMouseMotionListener(mouseHandler);
    }

    void checkForHover(MouseEvent event) {
        FontMetrics metrics = getFontMetrics(font);

        Graphics g = getGraphics();
        Rectangle textBounds = metrics.getStringBounds("A", g).getBounds();
        g.dispose();

        int index = 0;
        while (index < numberList.size()) {
            Double x = numberList.get(index).getCoordinate().getX();
            Double y = numberList.get(index).getCoordinate().getY();

            textBounds.translate(x.intValue(), y.intValue());

            if (textBounds.contains(event.getPoint())) {
                color = HOVER_TEXT_COLOR;
            }
            else {
                color = DEFAULT_TEXT_COLOR;
            }
            index++;
        }
        repaint(textBounds);
    }

    @Override
    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.setFont(font);
        g.setColor(color);

        int index = 0;
        while (index < numberList.size()) {
            Double x = numberList.get(index).getCoordinate().getX();
            Double y = numberList.get(index).getCoordinate().getY();
            String display = numberList.get(index).getDisplayString();
            g.drawString(display, x.intValue(), y.intValue());
            index++;
        }

        if (model.getCoordinate() != null) {
            Point p = model.getCoordinate();            
            g.drawString(model.getDisplayString(), p.x, p.y);
            GUIModel number = new GUIModel();
            number.setCoordinate(p);
            number.setDisplayString(model.getDisplayString());
            numberList.add(number);
        }
    }

    //class to handle all mouse events
    private class MouseHandler extends MouseAdapter implements MouseMotionListener
    {
        @Override
        public void mousePressed(MouseEvent event)
        {
           model.setCoordinate(event.getPoint());
        }

        @Override
        public void mouseReleased(MouseEvent event)
        {
            DrawPanel.this.repaint();
        }

        @Override
        public void mouseEntered(MouseEvent event) {
            checkForHover(event);
        }

        @Override
        public void mouseMoved(MouseEvent event) {
            checkForHover(event);
        }
    }
}

---

任何帮助都将不胜感激。谢谢

有几个误解

• Graphics#drawString

  不会在x/y位置绘制文本，因此x/y是

  字符串的左上角，而x/y位置是字体的基线，这意味着大部分文本绘制在y位置上方，有关详细信息，请参阅。这意味着，当您尝试计算文本的
  矩形时，它实际上低于绘制它的位置。相反，您需要使用
  y+ascent
  来正确定位文本
  paintComponent
  可以出于多种原因随时调用，其中许多原因您无法控制。为此，
  paintComponent
  应仅用于绘制组件的当前状态，不得更新或修改组件的状态。因此，在方法中添加新的
  GUIModel
  是错误的，相反，它应该添加到
  MouseListener
  的
  mouseClicked
  事件中
  您在很大程度上依赖于
  GUIModel
  变量。您应该仅在实际需要时创建模型
  

从概念上讲，这个例子解决了上面提到的大多数问题

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class DrawFrame extends JFrame {

    private final int WIDTH = 500;
    private final int HEIGHT = 300;

//  private GUIModel model;
    private JButton number1;
    private JButton number2;

    private JPanel numberPanel;
    private DrawPanel graphicsPanel;

    public DrawFrame() {
//      this.model = new GUIModel(" ");

        createSelectionPanel();
        createGraphicsPanel();

        this.setSize(WIDTH, HEIGHT);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    private void createSelectionPanel() {
        numberPanel = new JPanel();

        ButtonListener listener = new ButtonListener();

        number1 = new JButton("A");
        number1.addActionListener(listener);

        number2 = new JButton("B");
        number2.addActionListener(listener);

        numberPanel.setLayout(new GridLayout(2, 2));
        numberPanel.add(number1);
        numberPanel.add(number2);

        this.add(numberPanel, BorderLayout.WEST);
    }

    private void createGraphicsPanel() {
        //instantiate drawing panel
        graphicsPanel = new DrawPanel(WIDTH, HEIGHT);
        //add drawing panel to right
        add(graphicsPanel);
    }

    private class ButtonListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent event) {
            graphicsPanel.setDisplayString(event.getActionCommand());
        }
    }

    //creates a drawing frame
    public static void main(String[] args) {
        DrawFrame draw = new DrawFrame();
    }

    public static class DrawPanel extends JPanel {

        private static final long serialVersionUID = 3443814601865936618L;

        private Font font = new Font("Default", Font.BOLD, 30);

        private static final Color DEFAULT_TEXT_COLOR = Color.BLACK;
        private static final Color HOVER_TEXT_COLOR = Color.RED;
        private Color color = DEFAULT_TEXT_COLOR;

        private List<GUIModel> numberList = new ArrayList<GUIModel>();
        boolean mouseHover = false;

        private String displayString;
        private GUIModel hoverModel;

        public DrawPanel(int width, int height) {
            this.setPreferredSize(new Dimension(width, height));

            //set white background for drawing panel
            setBackground(Color.WHITE);

            //add mouse listeners
            MouseHandler mouseHandler = new MouseHandler();
            this.addMouseListener(mouseHandler);
            this.addMouseMotionListener(mouseHandler);
        }

        protected Rectangle getBounds(GUIModel model) {
            FontMetrics metrics = getFontMetrics(font);
            Double x = model.getCoordinate().getX();
            Double y = model.getCoordinate().getY();

            Rectangle textBounds = new Rectangle(
                    x.intValue(),
                    y.intValue(),
                    metrics.stringWidth(model.getDisplayString()),
                    metrics.getHeight());
            return textBounds;
        }

        void checkForHover(MouseEvent event) {

            Rectangle textBounds = null;
            if (hoverModel != null) {
                textBounds = getBounds(hoverModel);
            }
            hoverModel = null;
            if (textBounds != null) {
                repaint(textBounds);
            }
            for (GUIModel model : numberList) {

                textBounds = getBounds(model);

                if (textBounds.contains(event.getPoint())) {
                    hoverModel = model;
                    repaint(textBounds);
                    break;
                }
            }
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setFont(font);
            g.setColor(DEFAULT_TEXT_COLOR);

            FontMetrics fm = g.getFontMetrics();
            for (GUIModel model : numberList) {
                if (model != hoverModel) {
                    Double x = model.getCoordinate().getX();
                    Double y = model.getCoordinate().getY();
                    String display = model.getDisplayString();
                    g.drawString(display, x.intValue(), y.intValue() + fm.getAscent());
                }
            }
            if (hoverModel != null) {
                g.setColor(HOVER_TEXT_COLOR);
                Double x = hoverModel.getCoordinate().getX();
                Double y = hoverModel.getCoordinate().getY();
                String display = hoverModel.getDisplayString();
                g.drawString(display, x.intValue(), y.intValue() + fm.getAscent());
            }

//          if (model.getCoordinate() != null) {
//              Point p = model.getCoordinate();
//              g.drawString(model.getDisplayString(), p.x, p.y);
////                GUIModel number = new GUIModel();
////                number.setCoordinate(p);
////                number.setDisplayString(model.getDisplayString());
////                numberList.add(number);
//          }
        }

        public void setDisplayString(String text) {
            displayString = text;
        }

        //class to handle all mouse events
        private class MouseHandler extends MouseAdapter implements MouseMotionListener {

            @Override
            public void mouseClicked(MouseEvent e) {
                GUIModel model = new GUIModel(displayString);
                model.setCoordinate(e.getPoint());
                numberList.add(model);
                repaint();
            }

            @Override
            public void mouseMoved(MouseEvent event) {
                checkForHover(event);
            }
        }
    }

    public static class GUIModel {

        private String displayString;
        private Point coordinate;

        public GUIModel() {
        }

        public GUIModel(String displayString) {
            this.displayString = displayString;
        }

        public void setDisplayString(String displayString) {
            this.displayString = displayString;
        }

        public String getDisplayString() {
            return displayString;
        }

        public Point getCoordinate() {
            return coordinate;
        }

        public void setCoordinate(int x, int y) {
            this.coordinate = new Point(x, y);
        }

        public void setCoordinate(Point coordinate) {
            this.coordinate = coordinate;
        }
    }
}

导入java.awt.BorderLayout；
导入java.awt.Color；
导入java.awt.Dimension；
导入java.awt.Font；
导入java.awt.FontMetrics；
导入java.awt.Graphics；
导入java.awt.GridLayout；
导入java.awt.Point；
导入java.awt.Rectangle；
导入java.awt.event.ActionEvent；
导入java.awt.event.ActionListener；
导入java.awt.event.MouseAdapter；
导入java.awt.event.MouseEvent；
导入java.awt.event.MouseMotionListener；
导入java.util.ArrayList；
导入java.util.List；
导入javax.swing.JButton；
导入javax.swing.JFrame；
导入javax.swing.JPanel；
公共类DrawFrame扩展了JFrame{
专用最终整数宽度=500；
私人最终内部高度=300；
//私有gui模型；
私人按钮1号；
私人按钮2号；
私人JPanel号码panel；
私人拉丝板；
公共抽框（）{
//this.model=新的GUIModel（“”）；
createSelectionPanel（）；
createGraphicsPanel（）；
此.setSize（宽度、高度）；
此.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）；
此.setVisible（true）；
}
私有void createSelectionPanel（）{
numberPanel=新的JPanel（）；
ButtonListener侦听器=新建ButtonListener（）；
编号1=新的按钮（“A”）；
编号1.addActionListener（listener）；
数字2=新的按钮（“B”）；
编号2.addActionListener（listener）；
numberPanel.setLayout（新网格布局（2,2））；
数字面板添加（数字1）；
数字面板添加（数字2）；
添加（数字面板，BorderLayout.WEST）；
}
私有void createGraphicsPanel（）{
//实例化图形面板
graphicsPanel=新的绘图面板（宽度、高度）；
//将绘图面板添加到右侧
添加（图形spanel）；
}
私有类ButtonListener实现ActionListener{
@凌驾
已执行的公共无效操作（操作事件）{
graphicsPanel.setDisplayString（event.getActionCommand（））；
}
}
//创建绘图框
公共静态void main（字符串[]args）{
DrawFrame draw=新的DrawFrame（）；
}
公共静态类DrawPanel扩展了JPanel{
私有静态最终长serialVersionUID=3443814601865936618L；
私有字体字体=新字体（“默认”，Font.BOLD，30）；
私有静态最终颜色默认值\文本\颜色=Color.BLACK；
私有静态最终颜色悬停\文本\颜色=Color.RED；
专用颜色=默认的文本颜色；
private List numberList=new ArrayList（）；
布尔mouseHover=false；
私有字符串显示字符串；
私有图形用户界面模型；
公共绘图面板（内部宽度、内部高度）{
此.setPreferredSize（新尺寸（宽度、高度））；
//为绘图面板设置白色背景
挫折地面（颜色：白色）；
//添加鼠标侦听器
MouseHandler MouseHandler=新的MouseHandler（）；
这是addMouseListener（mouseHandler）；
this.addMouseMotionListener（mouseHandler）；
}
受保护的矩形getBounds（GUI模型）{
FontMetrics=getFontMetrics（字体）；
Double x=model.getCoordinate（）.getX（）；
双y=model.getCoordinate（）.getY（）；
矩形textBounds=新矩形(
x、 intValue（），
y、 intValue（），
metrics.stringWidth（model.getDisplayString（）），
metrics.getHeight（））；
返回文本边界；
}
void checkForHover（MouseEvent事件）{
矩形textBounds=null；
if（hoverModel！=null）{
textBounds=getBounds（hoverModel）；
}
hoverModel=null；
如果（textBounds！=null）{
重新绘制（文本边界）；
}
用于（GUI模型模型：numberList）{
textBounds=getBounds（模型）；
if（textBounds.contains（event.getPoint（）））{
模型=模型；
重新绘制（文本边界）；
打破
}
}
}
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class DrawFrame extends JFrame {

    private final int WIDTH = 500;
    private final int HEIGHT = 300;

//  private GUIModel model;
    private JButton number1;
    private JButton number2;

    private JPanel numberPanel;
    private DrawPanel graphicsPanel;

    public DrawFrame() {
//      this.model = new GUIModel(" ");

        createSelectionPanel();
        createGraphicsPanel();

        this.setSize(WIDTH, HEIGHT);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    private void createSelectionPanel() {
        numberPanel = new JPanel();

        ButtonListener listener = new ButtonListener();

        number1 = new JButton("A");
        number1.addActionListener(listener);

        number2 = new JButton("B");
        number2.addActionListener(listener);

        numberPanel.setLayout(new GridLayout(2, 2));
        numberPanel.add(number1);
        numberPanel.add(number2);

        this.add(numberPanel, BorderLayout.WEST);
    }

    private void createGraphicsPanel() {
        //instantiate drawing panel
        graphicsPanel = new DrawPanel(WIDTH, HEIGHT);
        //add drawing panel to right
        add(graphicsPanel);
    }

    private class ButtonListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent event) {
            graphicsPanel.setDisplayString(event.getActionCommand());
        }
    }

    //creates a drawing frame
    public static void main(String[] args) {
        DrawFrame draw = new DrawFrame();
    }

    public static class DrawPanel extends JPanel {

        private static final long serialVersionUID = 3443814601865936618L;

        private Font font = new Font("Default", Font.BOLD, 30);

        private static final Color DEFAULT_TEXT_COLOR = Color.BLACK;
        private static final Color HOVER_TEXT_COLOR = Color.RED;
        private Color color = DEFAULT_TEXT_COLOR;

        private List<GUIModel> numberList = new ArrayList<GUIModel>();
        boolean mouseHover = false;

        private String displayString;
        private GUIModel hoverModel;

        public DrawPanel(int width, int height) {
            this.setPreferredSize(new Dimension(width, height));

            //set white background for drawing panel
            setBackground(Color.WHITE);

            //add mouse listeners
            MouseHandler mouseHandler = new MouseHandler();
            this.addMouseListener(mouseHandler);
            this.addMouseMotionListener(mouseHandler);
        }

        protected Rectangle getBounds(GUIModel model) {
            FontMetrics metrics = getFontMetrics(font);
            Double x = model.getCoordinate().getX();
            Double y = model.getCoordinate().getY();

            Rectangle textBounds = new Rectangle(
                    x.intValue(),
                    y.intValue(),
                    metrics.stringWidth(model.getDisplayString()),
                    metrics.getHeight());
            return textBounds;
        }

        void checkForHover(MouseEvent event) {

            Rectangle textBounds = null;
            if (hoverModel != null) {
                textBounds = getBounds(hoverModel);
            }
            hoverModel = null;
            if (textBounds != null) {
                repaint(textBounds);
            }
            for (GUIModel model : numberList) {

                textBounds = getBounds(model);

                if (textBounds.contains(event.getPoint())) {
                    hoverModel = model;
                    repaint(textBounds);
                    break;
                }
            }
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setFont(font);
            g.setColor(DEFAULT_TEXT_COLOR);

            FontMetrics fm = g.getFontMetrics();
            for (GUIModel model : numberList) {
                if (model != hoverModel) {
                    Double x = model.getCoordinate().getX();
                    Double y = model.getCoordinate().getY();
                    String display = model.getDisplayString();
                    g.drawString(display, x.intValue(), y.intValue() + fm.getAscent());
                }
            }
            if (hoverModel != null) {
                g.setColor(HOVER_TEXT_COLOR);
                Double x = hoverModel.getCoordinate().getX();
                Double y = hoverModel.getCoordinate().getY();
                String display = hoverModel.getDisplayString();
                g.drawString(display, x.intValue(), y.intValue() + fm.getAscent());
            }

//          if (model.getCoordinate() != null) {
//              Point p = model.getCoordinate();
//              g.drawString(model.getDisplayString(), p.x, p.y);
////                GUIModel number = new GUIModel();
////                number.setCoordinate(p);
////                number.setDisplayString(model.getDisplayString());
////                numberList.add(number);
//          }
        }

        public void setDisplayString(String text) {
            displayString = text;
        }

        //class to handle all mouse events
        private class MouseHandler extends MouseAdapter implements MouseMotionListener {

            @Override
            public void mouseClicked(MouseEvent e) {
                GUIModel model = new GUIModel(displayString);
                model.setCoordinate(e.getPoint());
                numberList.add(model);
                repaint();
            }

            @Override
            public void mouseMoved(MouseEvent event) {
                checkForHover(event);
            }
        }
    }

    public static class GUIModel {

        private String displayString;
        private Point coordinate;

        public GUIModel() {
        }

        public GUIModel(String displayString) {
            this.displayString = displayString;
        }

        public void setDisplayString(String displayString) {
            this.displayString = displayString;
        }

        public String getDisplayString() {
            return displayString;
        }

        public Point getCoordinate() {
            return coordinate;
        }

        public void setCoordinate(int x, int y) {
            this.coordinate = new Point(x, y);
        }

        public void setCoordinate(Point coordinate) {
            this.coordinate = coordinate;
        }
    }
}