當按下按鈕，然後開始繪製按鈕也複製在面板

Question

我有兩個JPanel s。第一個包含JButton s，第二個包含鼠標。問題是當我點擊JButton並開始繪製JButton時也在JPanel上畫畫。請向我提供一些方向，關於我不看的地方？

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主類

public class LabelDemo extends JFrame { 

    JPanel p1 = new JPanel(); 
    painter p2 = new painter(); 
    JButton red = new JButton("red"); 
    JButton blue = new JButton(" blue "); 
    JLabel lbl = new JLabel("Label"); 
    ImageIcon icon = new ImageIcon("image/YouTube.png"); 

    public LabelDemo() { 

     setLayout(new BorderLayout()); 
     p1.setBorder(new LineBorder(Color.gray)); 
     //jbt1.setIcon(icon); 

     p1.add(red); 
     p1.add(blue); 
     lbl.setOpaque(true); 
     lbl.setBackground(Color.yellow); 
     p1.add(lbl); 
     p1.setBounds(20, 30, 40, 78); 
     add(p1,BorderLayout.EAST); 
     add(p2,BorderLayout.CENTER); 
    } 

    public static void main(String[] args){ 

     LabelDemo frame = new LabelDemo(); 
     frame.setVisible(true); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.setSize(700, 400); 
     frame.setLocationRelativeTo(null);    
    } 
} 

innr類

class painter extends JPanel { 

    int x , y; 
    boolean isPresed = false; 

    public void setPainter(int x , int y) {  
     this.x = x; 
     this.y = y; 
    } 

    public painter() { 

     addMouseMotionListener(new MouseMotionAdapter() {     
      public void mouseDragged(MouseEvent e) { 
       isPresed = true; 
       setPainter(e.getX(),e.getY()); 
       repaint(); 
      } 
     }); 
    } 

    protected void paintComponent(Graphics g){ 
     Color randomColor = Color.getHSBColor((float)Math.random(), 1.0F, 1.0F); 
     if(isPresed){      
      g.setColor(randomColor); 
      g.fillOval(x-5, y-5, 10, 10); 
     } 
    } 
}//end of painter 

Answer 1

好吧，我瞭解你要點擊紅色或藍色按鈕時得到東（P1面板）上去掉面板：

package stack; 

import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.awt.event.MouseEvent; 
import java.awt.event.MouseMotionAdapter; 

import javax.swing.*; 
import javax.swing.border.LineBorder; 

public class LabelDemo extends JFrame { 
    JPanel p1 = new JPanel(); 
    Painter p2 = new Painter(); 
    JButton red = new JButton("red"); 
    JButton blue = new JButton(" blue "); 
    JLabel lbl = new JLabel("Label"); 
    ImageIcon icon = new ImageIcon("image/YouTube.png"); 
    public LabelDemo() { 
     setLayout(new BorderLayout()); 
     p1.setBorder(new LineBorder(Color.gray)); 
//  jbt1.setIcon(icon); 
     p2.setPreferredSize(new Dimension(600,400)); 
     p1.add(red); 
     p1.add(blue); 
     lbl.setOpaque(true); 
     lbl.setBackground(Color.yellow); 
     p1.add(lbl); 
     p1.setBounds(20, 30, 40, 78); 
     add(p1,BorderLayout.EAST); 
     add(p2,BorderLayout.CENTER); 
     red.addActionListener(new ActionListener(){ 

     public void actionPerformed(ActionEvent e){ 
      remove(p1); 
      repaint(); 
      revalidate(); 
     } 
    }); 
    blue.addActionListener(new ActionListener(){ 

     public void actionPerformed(ActionEvent e){ 
      remove(p1); 
      repaint(); 
      revalidate(); 
     } 
    }); 
} 


    public static void main(String[] args){ 
     LabelDemo frame = new LabelDemo(); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.pack(); 
     frame.setVisible(true); 
    } 
} 
class Painter extends JPanel { 
    int x , y; 
    boolean isPresed = false; 
    public void setPainter(int x , int y) { 
    this.x = x; 
    this.y = y; 
} 
    public Painter() { 

    addMouseMotionListener(new MouseMotionAdapter() { 

     public void mouseDragged(MouseEvent e) { 
      isPresed = true; 
      setPainter(e.getX(),e.getY()); 
      repaint(); 
     } 
    }); 
} 

    protected void paintComponent(Graphics g){ 
     Color randomColor = Color.getHSBColor((float)Math.random(), 1.0F, 1.0F); 
    if(isPresed){ 

     g.setColor(randomColor); 
     g.fillOval(x-5, y-5, 10, 10); 
    } 
    } 
}//end of painter 

也不要調用setSize（）方法調用包（），並有必要對setPreferredSize（ ），因爲那個，我被個人批評了幾次。只是一個註釋。

Answer 2

在您的painter窗格的paintComponent方法中，您應該首先調用super.paintComponent。

Swing重複使用Graphics，因此可能會將舊內容仍保留在緩衝區中。如果你打電話給super.paintComponent，這會清理它

protected void paintComponent(Graphics g){ 
    // Must call super.paintComponent() so the Graphics is updated correctly... 
    super.paintComponent(); 
    Color randomColor = Color.getHSBColor((float)Math.random(), 1.0F, 1.0F); 
    if(isPresed){      
     g.setColor(randomColor); 
     g.fillOval(x-5, y-5, 10, 10); 
    } 
}