我有一个带有两个按钮的Jframe：＆＃39; A＆＃39;和＆＃39; B＆＃39;。点击按钮＆＃39; A＆＃39;应该在JPanel中显示大写字母A.在鼠标悬停时，任何＆＃39; A＆＃39;画布中的字母应显示为红色。当鼠标离开时，文本颜色应该恢复为黑色。
我为此编码了，它只能运行一次。这封信＆＃39; A＆＃39;变为红色但不会变回黑色。此外，它不适用于多个A＆＃39;
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的代码：
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;
}
}
非常感谢任何帮助。谢谢！
答案 0 :(得分：3)
有几个误解。
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都是在y位置上方绘制的，有关详细信息，请参阅Font Concepts。这意味着当您尝试计算文本的Rectangle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可以随时出于多种原因被调用，其中许多原因是您无法控制的。为此，paintComponent应仅用于绘制组件的当前状态，并且永远不应更新或修改组件的状态。因此，在方法中添加新的GUIModel是不对的，相反，它应该添加到mouseClicked的{{1}}事件中。MouseListener个变量。您应该只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
GUIModel