Trying to draw multiple polygons results in error

问题

Following my previous post here , I changed the code to :

PolygonnerJframe.java

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import java.util.Iterator;
import javax.swing.JFrame;
import javax.swing.JPanel;


/**
 * 
 * @author X2
 *
 */
public class PolygonnerJframe
{
    public static void main (String[] args)
    {
     JFrame frame = new JFrame("Draw polygons");
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     frame.setContentPane(new DrawingPanel());
     frame.pack();
     frame.setVisible(true);
 }
}

Now , this code results in :

And I can't understand what causes this .

The changes that I've made are : when we're done with a polygon , its coordinates are saved in the arrayList of class Polygon , and each time that I create a new polygon , I take the previous polygons and draw them , while drawing a new polygon .

As you can see above , something went wrong with the drawing and I can't seem to find the problem .

I'd appreciate any help .

Thanks

EDIT:

After taking into consideration what @StanislavL said , I moved those lines to mouseClicked() , but this time I get a new screen each time that a new polygon is created without the "old" polygons .

Just a new polygon ... without the old ones

回答1:

On each public void paintComponent(Graphics g) call you create a new polygon add add it to the polygons list.

        Polygon poly = new Polygon(this.edges);

        // add the polygon to the polygons array 
        this.polygons.add(poly);

Guess that should happen just one e.g. in the mouseClicked() processing

回答2:

@Stas code works for me witout any add_ons (added basic stuff cried in IDE), did you meaning final result could be ???

EDIT

dirty hack is disable super.paintComponent(g);, but proper way should be only

to add all Objects to the array (see quite clear comment by @ trashgod)
create an BurreferImage as Backgroung Image (after Mouse Double_Click)

output by disable super.paintComponent(g);

来源：https://stackoverflow.com/questions/15657010/trying-to-draw-multiple-polygons-results-in-error

标签

java

swing

jframe

awt