无法测试操作，因此无法更新 Applet

Question

我的主要问题是我对在哪里实现侦听器感到困惑 classes 以便无论何时执行操作（无论是按键还是鼠标单击）都会更新小程序。我意识到我的编译问题来自我的 CanvasPanel class 中的 CanvasPanel 方法，并且我的 actionPerformed 方法中没有参数。但是此时我不确定应该如何正确实现这些侦听器。已尝试查看已发布的不同问题，如果重复，我们深表歉意。

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

Answer 1

该代码中的一些主要问题：

您正在直接调用 paintComponent，这是您永远不应该做的事情。而是更改 class 的状态字段，调用 repaint()，然后让 paintComponent 使用状态字段来决定它应该绘制什么。
使用图形字段也是如此——不要。而是仅使用 JVM 提供给 paintComponent 方法的 Graphics 对象。 Swing Graphics tutorial will explain this.
您正在尝试直接调用您的侦听器回调方法，这与侦听器的工作方式完全相反，并且抵消了使用侦听器的好处。相反 ADD 您的监听器将使用它们的组件——包括将 ActionListeners 添加到需要它们的按钮，将 KeyListeners 添加到需要它们的组件需要它们，MouseListeners...等...

例如，让我们看一个更更简单的例子，一个使用两个 JRadioButtons 的例子就是这样：

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);
    }
}

这里我们向 JRadioButtons 添加一个 ColorListener。在侦听器中，我们更改 class 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什么颜色。

无法测试操作，因此无法更新 Applet

Am not able to test for actions, and therefore cannot update Applet

java

swing

applet