java - 使用 JSlider 上的 ChangeListener 更改 JPanel 上绘制线条的粗细

Question

我有一个 JSlider，它指定在 JPanel 上绘制的线条的粗细。我向其中添加了一个 ChangeListener，因此当 slider 更改时，它也应该更改线条的粗细。但是当我这样做时，粗细并没有改变，相反，我得到了一条淡出的线。当我没有 ChangeListener 时，初始颜色是紫色线。我不明白发生了什么事。

这是在我的主 GUI 类中，它包括 JSlider 和 ChangeListener:

    final JSlider slider = new JSlider(SwingConstants.HORIZONTAL, 0, 20, 1);

    slider.setMajorTickSpacing(5);
    slider.setMinorTickSpacing(1);
    slider.setPaintTicks(true);
    slider.setPaintLabels(true);

    slider.addChangeListener(new ChangeListener() {
        public void stateChanged(final ChangeEvent theEvent) {
            final int stroke = slider.getValue();
            myDrawPanel.setStroke(stroke);
            myDrawPanel.repaint();
        }
    });

这是在另一个类中绘制线的:

public void setStroke(final int theStroke) {
    myStroke = theStroke;
}

public void paintComponent(final Graphics theGraphics) {
    super.paintComponent(theGraphics);
    final Graphics2D g2d = (Graphics2D) theGraphics;

    // for better graphics display
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                         RenderingHints.VALUE_ANTIALIAS_ON);

    g2d.setPaint(new Color(51, 0, 111));
    g2d.setStroke(new BasicStroke(myStroke));

    g2d.draw(new Line2D.Double(myX, myY, myXEnd, myYEnd));

    for (Line2D l : myLines) {
        g2d.draw(l);
    } 
}

这就是结果:

这就是我在 PaintComponent 方法中硬编码线条粗细数字时线条最初的样子:

Answer 1

似乎对我来说工作正常，我想问题出在您没有向我们展示的代码中的其他地方

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class Example {

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

    public Example() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new ControlPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class ControlPane extends JPanel {

        public ControlPane() {
            setLayout(new BorderLayout());

            DrawPane pane = new DrawPane();
            add(pane);

            JSlider slider = new JSlider(0, 20, 1);
            add(slider, BorderLayout.SOUTH);

            slider.addChangeListener(new ChangeListener() {
                @Override
                public void stateChanged(ChangeEvent e) {
                    pane.setStroke(slider.getValue());
                }
            });
            slider.setValue(1);
        }

    }

    public class DrawPane extends JPanel {

        private int myStroke = 1;

        public DrawPane() {
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        public void setStroke(int myStroke) {
            this.myStroke = myStroke;
            repaint();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setStroke(new BasicStroke(myStroke));
            g2d.drawLine(0, 0, getWidth(), getHeight());
            g2d.dispose();
        }

    }

}

考虑提供 runnable example这说明了你的问题。这不是代码转储，而是您正在执行的操作的示例，它突出显示了您遇到的问题。这将减少困惑并获得更好的响应