java - 仅更改鼠标悬停时字母的颜色

标签 java swing paintcomponent repaint mousehover

我有一个带有两个按钮的 Jframe:“A”和“B”。单击按钮“A”应在 JPanel 中显示大写字母 A。仅当鼠标悬停时， Canvas 内的任何“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，但它只能运行一次。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 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 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);
        }
    }
}

GUIModel 代码:

import java.awt.Point;

public 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;
    }   
}

任何帮助将不胜感激。谢谢!

最佳答案

存在一些误解。

  • Graphics#drawString 不会在 x/y 位置绘制文本，因此 x/y 是 String 的左上角，而是，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，请参阅 Font Concepts更多细节。这意味着当您尝试计算文本的矩形时，它实际上低于您绘制它的位置。相反，您需要使用 y + ascent 来使文本正确定位。
  • paintComponent 可以出于多种原因随时调用，其中许多原因是您无法控制的。为此，paintComponent 应该只用于绘制组件的当前状态，并且永远不应该更新或修改组件的状态。因此，在方法中添加新的 GUIModel 是错误的做法，而应该将其添加到 MouseListener 的 mouseClicked 事件中。
  • 您非常依赖 GUIModel 变量。您应该仅在实际需要时创建模型

从概念上讲，此示例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;
        }
    }
}

关于java - 仅更改鼠标悬停时字母的颜色，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33772839/

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