drawLine JAVA不會停留在MAC OS X上

Question

首先，這個問題僅在os x上有效，我不知道為什么，如果有人能告訴我...（他在linux和Windows上都能正常工作）

當我單擊繪制時，舊點消失而不是留下。 如果刪除super.paintComponent上的注釋 ，則在osx上的結果相同，但在window和linux上的結果不同。

單擊以繪制。

import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Stack extends JPanel {
    JFrame jf;
    Panneau jp;
    Point p;

    public Stack() {
        p = new Point();
        jf = new JFrame("Window");
        jp = new Panneau();
        jp.setBackground(Color.white);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setSize(800,600);
        jf.setLayout(new GridLayout());
        jf.add(jp);
        jf.setVisible(true);

        jp.addMouseListener(new MouseAdapter(){
            public void mouseClicked(MouseEvent e){
               setPoint(p);
               jp.repaint();
            }
        });
    }

    public void setPoint(Point p) {
        this.p.x += 10;
        this.p.y += 10;
    }

    public class Panneau extends JPanel {
        public void paintComponent(Graphics g) {
            // super.paintComponent(g);
            g.drawLine(p.x, p.y, p.x+5, p.y+5);
        }
    }

    public static void main (String []args) {
        Stack s = new Stack();
    }
}

Answer 1

發生這種情況是因為您沒有重繪以前的點所在的區域，顯然在Mac上，由於某些原因，它確實重繪了該區域嗎？

但是要點是，您不應該依靠繪制更多的點而不是在先前的區域上繪制，而應該始終調用super.paintComponent（g）。 我建議您創建一個點列表，然后在重新繪制時繪制所有這些點。

我已經自由創建了自己的代碼，希望您了解我在這里做什么：

import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Stack extends JPanel {
    JFrame jf;
    Panneau jp;
    //List of points instead of one point
    List<Point> points;

    public Stack() {
        //Instantiating the list
        points = new ArrayList<Point>();
        jf = new JFrame("Window");
        jp = new Panneau();
        jp.setBackground(Color.white);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setSize(800,600);
        jf.setLayout(new GridLayout());
        jf.add(jp);
        jf.setVisible(true);

        jp.addMouseListener(new MouseAdapter(){
            public void mouseClicked(MouseEvent e){
                //Adding a new point to the list
                addPoint();
                jp.repaint();
            }
        });
    }

    public void addPoint() {
        if(points.isEmpty()){
            //If this is the first point to be added, set it to 0,0
            points.add(new Point(0, 0));
        }else{
            //Get the last point currently in the list
            Point lastPoint = points.get(points.size()-1);
            //Create the newpoint, 10px right and 10px down from the current point
            Point newPoint = new Point(lastPoint.x + 10, lastPoint.y + 10);
            //Add the new point to the list
            points.add(newPoint);
        }
    }

    public class Panneau extends JPanel {
        public void paintComponent(Graphics g) {
            //Make sure the background is drawn! Should always be called
            super.paintComponent(g);
            //Iterate over all the points and draw them all
            for(Point p : points){
                g.drawLine(p.x, p.y, p.x + 5, p.y + 5);
            }
        }
    }

    public static void main (String []args) {
        Stack s = new Stack();
    }
}