How can I draw a curved line segment using QuadCurve2D.Double?

问题

Here is the line of code where I declare the curve:

QuadCurve2D.Double curve = new QuadCurve2D.Double(50,100,100,170,150,100);

Now what code can I use to draw this curve? I tried something like:

g.draw(curve);

but obviously that didn't work. Any suggestions?

回答1:

I've made a minimum test case of what I think your describing here. This program works but I can't really help you unless I can see the code you are working with.

import java.awt.geom.*;
import java.awt.*;
import javax.swing.*;

public class CurveDraw extends JFrame {
        public static void main(String[] args) {
                CurveDraw frame = new CurveDraw();
                frame.setVisible(true);
        }
        public CurveDraw() {
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                setSize(400,400);
        }
        public void paint(Graphics g) {
                QuadCurve2D.Double curve = new QuadCurve2D.Double(50,100,100,170,150,100);
                ((Graphics2D)g).draw(curve);
        }
}

回答2:

Works fine for me...

public class PaintQuad {

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

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

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new PaintMyQuad());
                frame.setSize(200, 200);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class PaintMyQuad extends JPanel {

        @Override
        protected void paintComponent(Graphics g) {

            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            QuadCurve2D.Double curve = new QuadCurve2D.Double(50,100,100,170,150,100);

            g2d.setColor(Color.RED);
            g2d.draw(curve);

        }

    }

}

Two things come to mind.

Make sure you've set the color of the graphics, the default is the back ground color of the pane
Make sure that the size of your container is large enough (and is layout correctly) to show the graphics.

来源：https://stackoverflow.com/questions/13114483/how-can-i-draw-a-curved-line-segment-using-quadcurve2d-double

标签

java

swing

graphics2d

paintcomponent