Java:无法显示paintComponent

Question

我一直在尝试开发一个带有带箭头的人物简笔画的程序。所以这里的问题是，当添加 ImageIcon 作为背景时，paintComponent 下的绘图不会显示。如何在背景图像之上显示这幅画。我的编码如下。

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;
    }
}
}

我还在学习Java，有人可以帮助解决这个问题吗？谢谢。

Answer 1

如果您想在 Swing 应用程序中使用不同的层，则应该使用 LayeredPane 而不是 JPanel。并且您应该避免设置不同的 LayoutManager。这段代码设置了最后一个LayoutManager，所以第一行没用:

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

这里有一篇关于如何使用 LayeredPanes 的文章 Tutorial