添加到 JButton 的 ActionListener 和 MouseListener 都不能在 JPanel 的 PaintComponent 中設置顏色

Question

我正在創建一個 Java 程序來模擬 Windows 95 中的 Microsoft Paint。底部有一個調色板。 單擊調色板中的任何顏色都會更改鉛筆等繪畫工具的顏色。 我嘗試使用 Graphics2D 根據在調色板中單擊的按鈕設置工具的每種顏色。 我嘗試將 ActionListener 添加到表示調色板中顏色按鈕的 JButton，然后將其更改為 MouseListener。 但是我的代碼不適用於此目的。 我不確定這是否會發生，因為 ActionListener/MouseListener 包含在 for 循環中，然后包含在 MouseMotionListener 中。 在此代碼中，添加到 JButton 的 ActionListener 和 MouseListener 均無法在 JPanel 中的 PaintComponent 中設置顏色。 有沒有更好的方法來重寫這段代碼？

這是我創建的 Paint 模擬的屏幕截圖：在此處輸入圖像描述

我的代碼如下：

paintOpen = new JFrame();
paintCanvasPanel = new JPanel() {
  private static final long serialVersionUID = 1L;
  public void paintComponent(Graphics g) {
    this.addMouseMotionListener(new MouseMotionListener() {
      public void mouseDragged(MouseEvent e) {
        if (SwingUtilities.isLeftMouseButton(e)) {
          Graphics2D g = (Graphics2D) getGraphics();
          g.drawLine(e.getX(), e.getY(), e.getXOnScreen(), e.getYOnScreen());
          g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
          g.setStroke(new BasicStroke(WIDTH, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_BEVEL));
          for (int i = 0; i < 28; i++) {
            //Neither ActionListener nor MouseListener works
            paintColorButton[i].addMouseListener(new MouseAdapter() {
              public void mousePressed(MouseEvent e) {
                for (int j = 0; j < 28; j++) {
                  g.setColor(paintPaletteColor[j]);
                }
              }

            });
          }
        }
      }
      public void mouseMoved(MouseEvent e) {

      }
    });

  }
};
paintScrollPane = new JScrollPane(paintCanvasPanel);
paintScrollPane.setBackground(white);
paintScrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
paintScrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
paintOpen.getContentPane().add(paintScrollPane);
paintOpen.getContentPane().setBackground(white);
paintOpen.setAlwaysOnTop(true);
paintOpen.setBounds(200, 0, 420, 600);
paintOpen.setExtendedState(JFrame.MAXIMIZED_BOTH);
paintOpen.setIconImage(paintIcon.getImage());
paintOpen.setTitle("untitled - Paint");
paintPalettePanel = new JPanel();
paintColorButton = new JButton[28];
for (int i = 0; i < 28; i++) {
  paintColorButton[i] = new JButton();
  paintColorButton[i].setBackground(paintPaletteColor[i]);
  paintPalettePanel.add(paintColorButton[i]);
}
paintOpen.add(paintPalettePanel, BorderLayout.SOUTH);
}

我嘗試將ActionListener 更改為MouseListener，但仍然無法更改顏色。

            for (int i = 0; i < 28; i++) {
              paintColorButton[i].addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                  for (int j = 0; j < 28; j++) {
                    g.setColor(paintPaletteColor[j]);
                  }
                }

              });
            }

Answer 1

我不確定這是否有任何幫助，但我拿了你的代碼，整理了一下，刪除了多余的並添加了缺失的。 我只能建議你仔細看看事情。 Swing 是面向事件的，您必須記住何時移動鼠標或按下按鈕，以便能夠在paintComponent事件中處理此信息。 在這種情況下，必須在mouseDragged中調用repaint()以便結果可見。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class PaintPanel extends JPanel implements MouseMotionListener, ActionListener{
    private Color[] paintPaletteColor = { Color.BLACK, Color.BLUE, Color.CYAN, Color.DARK_GRAY, Color.GRAY, Color.GREEN, Color.LIGHT_GRAY, Color.MAGENTA, Color.ORANGE, Color.PINK, Color.RED, Color.WHITE, Color.YELLOW };
    private Color drawColor = Color.BLACK;
    private MouseEvent e;

    public static void main(String[] args) {
        new PaintPanel();
    }

    public PaintPanel() {
        addMouseMotionListener(this);
        setPreferredSize(new Dimension(1024, 768));

        JScrollPane paintScrollPane = new JScrollPane(this);
        paintScrollPane.setBackground(Color.WHITE);
        paintScrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        paintScrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        paintScrollPane.setBackground(Color.white);

        JPanel paintPalettePanel = new JPanel();
        // Add a button for each color defined in paintPaletteColor. 
        // Add more colors there for additional buttons.
        for (int i = 0; i < paintPaletteColor.length; i++) {
            JButton button = new JButton();
            button.setBackground(paintPaletteColor[i]);
            button.addActionListener(this);
            paintPalettePanel.add(button);
        }

        JFrame paintOpen = new JFrame();
        paintOpen.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        paintOpen.add(paintScrollPane);
        paintOpen.add(paintPalettePanel, BorderLayout.SOUTH);
        paintOpen.setIconImage(new ImageIcon("Icon.png").getImage());
        paintOpen.setTitle("untitled - Paint");
        paintOpen.pack();
        paintOpen.setLocationRelativeTo(null);
        paintOpen.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // A button was clicked - remember its color.
        drawColor = ((JButton)e.getSource()).getBackground();
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        // The mouse was dragged - remember the new position and repaint the panel.
        this.e = e;
        repaint();
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        //
    }

    @Override
    public void paintComponent(Graphics g) {
        // triggered `repaint`, so let's go.
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setStroke(new BasicStroke(4, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_BEVEL));
        g2d.setColor(drawColor);
        // mouse dragged ? 
        if(e != null) g2d.drawLine(e.getX(), e.getY(), e.getX(), e.getY());
    }
}