我的主要问题是我对实现侦听器类的位置感到困惑，因此无论何时进行操作（无论是按键还是鼠标单击），applet都会更新。我意识到我的编译问题来自我的CanvasPanel类中的CanvasPanel方法，而且我的actionPerformed方法中没有参数。但是在这一点上，我不确定这些听众应该如何正确实施。尝试查看已发布的不同问题，如果它是重复的话，请对不起。
这是我的代码：
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class WholePanel extends JPanel
{
private Color foregroundColor, backgroundColor;
private int currentDiameter, x1, y1;
private CanvasPanel canvas;
private JPanel buttonPanel;
private JRadioButton filledRadio, unfilledRadio;
private JRadioButton redRadio, greenRadio;
private boolean fill;
private Graphics myCircle;
public WholePanel()
{
backgroundColor = Color.CYAN;
foregroundColor = Color.RED;
currentDiameter = 100;
x1 = 200; y1 = 100;
unfilledRadio = new JRadioButton("Unfilled", true);
filledRadio = new JRadioButton("Filled", false);
redRadio = new JRadioButton("Red", true);
greenRadio = new JRadioButton("Green", false);
buttonPanel = new JPanel();
buttonPanel.add(unfilledRadio);
buttonPanel.add(filledRadio);
buttonPanel.add(redRadio);
buttonPanel.add(greenRadio);
canvas = new CanvasPanel();
JSplitPane sPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT, buttonPanel, canvas);
setLayout(new BorderLayout());
add(sPane, BorderLayout.CENTER);
}
private class ColorListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
if (redRadio.isSelected()) {
greenRadio.setSelected(false);
backgroundColor = Color.RED;
}
else if (greenRadio.isSelected()) {
redRadio.setSelected(false);
backgroundColor = Color.GREEN;
}
// ...extra else/if statements
}
} // end of ColorListener
private class FillListener implements ActionListener
{
private boolean fill;
public void actionPerformed(ActionEvent event)
{
if (filledRadio.isSelected()) {
unfilledRadio.setSelected(false);
fill = true;
paintComponent(myCircle);
}
else if (unfilledRadio.isSelected()) {
filledRadio.setSelected(false);
fill = false;
paintComponent(myCircle);
}
}
}
private class CanvasPanel extends JPanel
{
public CanvasPanel( )
{
addKeyListener(new DirectionListener());
addMouseListener(new PointListener());
setBackground(backgroundColor);
//This method needs to be called for this panel to listen to keys
//When panel listens to other things, and go back to listen
//to keys, this method needs to be called again.
ColorListener.actionPerformed();
FillListener.actionPerformed();
requestFocus();
}
public void paintComponent(Graphics page)
{
super.paintComponent(page);
setBackground(backgroundColor);
page.setColor(foregroundColor);
page.drawOval(x1, y1, currentDiameter, currentDiameter);
if (fill == true) {
page.fillOval(x1, y1, currentDiameter, currentDiameter);
}
}
/** This method is overriden to enable keyboard focus */
public boolean isFocusable()
{
return true;
}
private class DirectionListener implements KeyListener
{
public void keyReleased(KeyEvent e) {}
public void keyTyped(KeyEvent e) {}
public void keyPressed(KeyEvent e)
{
currentDiameter = 100;
x1 = 200; y1 = 100;
int keyCode = e.getKeyCode();
// switch statement here
}
}
} // end of DirectionListener
public class PointListener implements MouseListener
{
public void mousePressed (MouseEvent event)
{
canvas.requestFocus();
}
public void mouseClicked (MouseEvent event) {}
public void mouseReleased (MouseEvent event) {}
public void mouseEntered (MouseEvent event) {}
public void mouseExited (MouseEvent event) {}
} // end of PointListener
} // end of Canvas Panel Class
} // end of Whole Panel Class
答案 0 :(得分：2)
该代码中的一些主要问题：
repaint()然后让paintComponent使用state字段来决定它应该绘制什么。例如，让我们看一个很多更简单的例子，一个使用两个JRadioButton的例子：＆/ p>
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
@SuppressWarnings("serial")
public class PartialPanel extends JPanel {
private static final int PREF_W = 800;
private static final int PREF_H = 650;
private static final int CIRC_W = 200;
private int circleX = 300;
private int circleY = 200;
private Color circleColor = null;
private ButtonGroup buttonGroup = new ButtonGroup();
private JRadioButton blueButton = new JRadioButton("Blue");
private JRadioButton redButton = new JRadioButton("Red");
public PartialPanel() {
ColorListener colorListener = new ColorListener();
blueButton.addActionListener(colorListener);
redButton.addActionListener(colorListener);
buttonGroup.add(blueButton);
buttonGroup.add(redButton);
JPanel buttonPanel = new JPanel();
buttonPanel.add(blueButton);
buttonPanel.add(redButton);
add(buttonPanel);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (circleColor != null) {
g.setColor(circleColor);
g.fillOval(circleX, circleY, CIRC_W, CIRC_W);
}
}
@Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
} else {
return new Dimension(PREF_W, PREF_H);
}
}
private class ColorListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == blueButton) {
circleColor = Color.BLUE;
} else if (e.getSource() == redButton) {
circleColor = Color.RED;
}
repaint();
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
private static void createAndShowGui() {
PartialPanel mainPanel = new PartialPanel();
JFrame frame = new JFrame("PartialPanel");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.add(mainPanel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
这里我们将一个ColorListener添加到JRadioButtons。在监听器中，我们改变类的circColor字段的状态，然后调用repaint（）。然后paintComponent方法使用circColor的值来决定绘制圆时使用的颜色。