绘制程序：Array向后写入面板

Question

我之前发布了这个代码，得到了一个非常好的答案，但没有一个可行的答案。有人可以告诉我如何更改我的代码，以便修复这个问题吗？这将运行并编译。它应该在一条线的顶部绘制一条线，而是在前一条线的下方绘制。我试过使用Collections.reverse（段）;但它没有考虑元素为零。我也尝试改为segments.add（new Segment（））;但我不确定要在MouseMotionListener中更改哪些内容才能使其正常工作。任何帮助，这将是伟大的！谢谢！ :)

import java.awt.*; 
import java.awt.event.*; 
import java.awt.geom.*; 
import java.util.ArrayList; 
import java.util.List; 
import javax.swing.*; 

public class SimplePaint extends JFrame implements ActionListener { 

private static final long serialVersionUID = 1L; 
JButton action = new JButton(); 
JButton red = new JButton(); 
JButton blue = new JButton(); 
JButton yellow = new JButton(); 
Color initial = Color.MAGENTA; 
JButton thin = new JButton(); 
JButton medium = new JButton(); 
JButton thick = new JButton(); 
Stroke stroke = new BasicStroke(3); 
private static ArrayList<Point> points = new ArrayList<Point>(); 

JButton erase = new JButton(); 
JButton drawing = new JButton(); 
Point start = null; 
Point end = null; 
Line2D draw = new Line2D.Float(); 
JPanel panel = new JPanel(); 

private class Segment { 
    private final List<Point> points = new ArrayList<Point>(); 
    private final Color color = initial; 
    private final Stroke stroke = SimplePaint.this.stroke; 
} 

private final List<Segment> segments = new ArrayList<>(); 

public SimplePaint() { 
    getContentPane().add(panel); 
    setSize(450, 450); 
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

    design(); 

    addMouseListener(new MouseAdapter() { 
     public void mousePressed(MouseEvent e) { 
      segments.add(0, new Segment()); 
     } 
    }); 

    addMouseMotionListener(new MouseMotionAdapter() { 
     public void mouseDragged(MouseEvent e) { 
      segments.get(0).points.add(e.getPoint()); 
      repaint(); 
     } 
    }); 

    addMouseMotionListener(new MouseMotionAdapter(){ 

     @Override 
     public void mouseDragged(MouseEvent e){ 
      points.add(e.getPoint()); 
      repaint(); 
     } 
    }); 

    blue.addActionListener(this); 
    red.addActionListener(this); 
    yellow.addActionListener(this); 
    thin.addActionListener(this); 
    medium.addActionListener(this); 
    thick.addActionListener(this); 
    erase.addActionListener(this); 
    drawing.addActionListener(this); 
} 

public void design() { 
    panel.setBackground(Color.BLACK); 

    blue.setBackground(Color.BLUE); 
    blue.setPreferredSize(new Dimension(50, 25)); 
    panel.add(blue); 

    red.setBackground(Color.RED); 
    red.setPreferredSize(new Dimension(50, 25)); 
    panel.add(red); 

    yellow.setBackground(Color.yellow); 
    yellow.setPreferredSize(new Dimension(50, 25)); 
    panel.add(yellow); 

    thin.setText("Thin"); 
    panel.add(thin); 

    medium.setText("Medium"); 
    panel.add(medium); 

    thick.setText("Thick"); 
    panel.add(thick); 

    erase.setText("Erase"); 
    panel.add(erase); 

    drawing.setText("Draw"); 
    panel.add(drawing); 
} 

public void actionPerformed(ActionEvent e) { 
    if(e.getSource() == blue){ 
     initial = Color.BLUE; 
    }else if(e.getSource() == red){ 
     initial = Color.RED; 
    }else if(e.getSource() == yellow){ 
     initial = Color.YELLOW; 
    }else if(e.getSource() == thin){ 
     stroke = new BasicStroke(1); 
    }else if(e.getSource() == medium){ 
     stroke = new BasicStroke(5); 
    }else if(e.getSource() == thick){ 
     stroke = new BasicStroke(10); 
    }else if(e.getSource() == erase){ 
     initial = Color.WHITE; 
     stroke = new BasicStroke(15); 
    } 

    //repaint(); 
} 

@Override 
public void paint(Graphics g) { 
    super.paint(g); 
    Graphics2D g2 = (Graphics2D) g; 

    int x1, y1, x2, y2; 

    for (Segment segment : segments) { 
     g2.setColor(segment.color); 
     g2.setStroke(segment.stroke); 

     for (int p = 0; p < segment.points.size() - 1; p++) { 
      x1 = segment.points.get(p).x; 
      y1 = segment.points.get(p).y; 
      x2 = segment.points.get(p + 1).x; 
      y2 = segment.points.get(p + 1).y; 
      g2.drawLine(x1, y1, x2, y2); 


     } 

    } 
    g2.dispose(); 

} 

public static void main(String []args){ 
    SimplePaint s = new SimplePaint(); 
    s.setVisible(true); 
} 
} 

Answer 1

要解决你的问题，你需要添加到List的结束，而不是开始：

addMouseListener(new MouseAdapter() { 
    @Override 
    public void mousePressed(MouseEvent e) { 
     segments.add(new Segment()); 
    } 
}); 

addMouseMotionListener(new MouseMotionAdapter() { 
    @Override 
    public void mouseDragged(MouseEvent e) { 
     segments.get(segments.size() - 1).points.add(e.getPoint()); 
     repaint(); 
    } 
}); 

此外，第二mouseDragged()实现冗余出现，如果你删除它，它仍然按预期运行。

// Can be removed 
addMouseMotionListener(new MouseMotionAdapter() {  
    @Override 
    public void mouseDragged(MouseEvent e) { 
     points.add(e.getPoint()); 
     repaint(); 
    } 
}); 

此外，你应该使用JComponent或JPanel画草图，@OverridepaintComponent()而不是paint()这种方法。这将有助于（或完全）消除您看到的闪烁。加上javax.swing.Timer到repaint()，而不是拖动，这可能会非常快速地（并且不必要地）更新。

最后，您应该确保您的GUI在事件调度线程上使用SwingUtilities.invokeLater(Runnable doRun)运行，因为Swing objects are not thread safe。

例如

public static void main(String[] args) { 
    SwingUtilities.invokeLater(new Runnable() { 
     public void run() { 
      SimplePaint s = new SimplePaint(); 
      s.setVisible(true); 
     } 
    }); 
}