Java：無法顯示paintComponent

我一直在試圖開發一個帶有箭頭的人類簡筆畫的程序。所以這裏的問題是，添加了ImageIcon作爲背景後，paintComponent下的圖形不會顯示。我如何在背景圖片上顯示繪畫。我的編碼如下。Java：無法顯示paintComponent

public class Drawing 
{ 
public Drawing() 
{ 
    JFrame f = new JFrame(); 
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    //f.getContentPane().setBackground(new Color(204,229,255)); 
    f.getContentPane().add(new ArrowPanel()); 
    f.setSize(1000,600); 
    //f.setLocation(200,200); 
    f.setLayout(new BorderLayout()); 
    f.setContentPane(new JLabel(new ImageIcon("/Users/marian/NetBeansProjects/Drawing/src/drawing/wall.jpg"))); 
    f.setLayout(new FlowLayout()); 
    f.setVisible(true); 
} 

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

class ArrowPanel extends JPanel 
{ 
double phi; 
int barb; 

public ArrowPanel() 
{ 
    phi = Math.toRadians(40); 
    barb = 30; 
} 

protected void paintComponent(Graphics g) 
{ 
    super.paintComponent(g); 
    Graphics2D g2 = (Graphics2D)g; 
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
         RenderingHints.VALUE_ANTIALIAS_ON); 
    int w = getWidth(); 
    int h = getHeight(); 
    Point sw = new Point(w/8, h*7/8); 
    Point ne = new Point(w*7/8, h/8); 
    g2.draw(new Line2D.Double(sw, ne)); 
    //drawArrowHead(g2, sw, ne, Color.red); 
    drawArrowHead(g2, ne, sw, Color.blue); 

    Ellipse2D.Double head = new Ellipse2D.Double(90,60,20,20); 
    g2.draw(head); 

    Line2D.Double body=new Line2D.Double(100,80,100,120); 
    g2.draw(body); 
    Line2D.Double arm1=new Line2D.Double(100,100,80,100); 
    g2.draw(arm1); 
    Line2D.Double arm2=new Line2D.Double(100,100,120,75); 
    g2.draw(arm2); 
    Line2D.Double leg1=new Line2D.Double(100,120,85,135); 
    g2.draw(leg1); 
    Line2D.Double leg2=new Line2D.Double(100,120,115,135); 
    g2.draw(leg2); 
    } 

private void drawArrowHead(Graphics2D g2, Point tip, Point tail, Color color) 
{ 
    g2.setPaint(color); 
    double dy = tip.y - tail.y; 
    double dx = tip.x - tail.x; 
    double theta = Math.atan2(dy, dx); 
    //System.out.println("theta = " + Math.toDegrees(theta)); 
    double x, y, rho = theta + phi; 
    for(int j = 0; j < 2; j++) 
    { 
     x = tip.x - barb * Math.cos(rho); 
     y = tip.y - barb * Math.sin(rho); 
     g2.draw(new Line2D.Double(tip.x, tip.y, x, y)); 
     rho = theta - phi; 
    } 
} 
}

我還在學習Java，有人可以幫助解決這個問題。謝謝。

來源

2017-05-12 marian

如果要在Swing應用程序中使用不同的圖層，應該使用LayeredPane而不是JPanel。你應該避免設置不同的佈局管理器。此代碼設置上次佈局管理，所以，第一行是沒用的：

f.setLayout(new BorderLayout()); 
f.setContentPane(new JLabel(new ImageIcon("/Users/marian/NetBeansProjects/Drawing/src/drawing/wall.jpg"))); 
f.setLayout(new FlowLayout());

下面是關於如何使用LayeredPanes Tutorial

來源

2017-05-12 10:57:45

的文章，你用的setContentPane()的調用替換您ArrowPanel：

f.getContentPane().add(new ArrowPanel()); 
... 
f.setContentPane(new JLabel(new ImageIcon("/Users/marian/NetBeansProjects/Drawing/src/drawing/wall.jpg")));

請嘗試更改這兩條語句的順序，EG把getContentPane()撥打後,setContentPane()。

來源

2017-05-12 12:52:08

Java：無法顯示paintComponent

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