Question

我有一个程序基本上只是在光标进入JPanel上显示的多边形时更改标签的文本。我尝试了一些不同的东西，没有任何工作。目前我正在尝试使用if语句来选择要添加的按钮，但如果我将光标移动到多边形中，它仍然不会改变。当光标在多边形之外时，标签应该说＆＃34;点不在多边形中＃34;当它在里面它应该说＆＃34;点在多边形＆＃34;。任何帮助将不胜感激。

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;

public class Chapter3Lab1  extends JFrame{

private RegularPolygonPanel canvas = new RegularPolygonPanel();

public Chapter3Lab1()
{

    JPanel panel = new JPanel();


    add(canvas, BorderLayout.CENTER);
    add(panel, BorderLayout.SOUTH);


    canvas.setFocusable(true);
    canvas.requestFocusInWindow();



}


public static void main (String[] args)
{

     String isInside = "The point is in the polygon";
     String notInside = "The point is not in the polygon";


     //Create a Polygon object
     Polygon polygon = new Polygon();

    polygon.addPoint(40,20);
    polygon.addPoint(70,40);
    polygon.addPoint(60,80);
    polygon.addPoint(45,45);
    polygon.addPoint(20,60);


    JLabel label = new JLabel(isInside, JLabel.CENTER);
    JLabel notlabel = new JLabel(notInside, JLabel.CENTER);

    Chapter3Lab1 frame = new Chapter3Lab1();;
    frame.setTitle("Chapter 3 Lab 1");
    frame.setLayout(new FlowLayout());
    frame.setLocationRelativeTo(null);// Center the frame
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(200,200);
    while (true)
    {
        PointerInfo a = MouseInfo.getPointerInfo();
        Point b = a.getLocation();
        int x = (int) b.getX();
        int y = (int) b.getY();
        if(polygon.contains(x, y) == false)
        {
        frame.remove(label);
        frame.add(notlabel);
        }
        else 
        {
        frame.remove(notlabel);
        frame.add(label);
        }

        frame.setVisible(true);
        try
        {
            Thread.sleep(1000);
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }



}

class RegularPolygonPanel extends JPanel
{




     protected void paintComponent(Graphics g)
     {
         super.paintComponent(g);

         //Create a Polygon object
         Polygon polygon = new Polygon();

        polygon.addPoint(40,20);
        polygon.addPoint(70,40);
        polygon.addPoint(60,80);
        polygon.addPoint(45,45);
        polygon.addPoint(20,60);

         //Draw the polygon
         g.drawPolygon(polygon);
     }

     public Dimension getPreferredSize()
     {
         return new Dimension(200,200);
     }
}
}

Answer 1

首先看一下How to Write a Mouse Listener

您需要维护对Polygon对象的引用，并使用它的contains方法来确定鼠标是否在Polygon内...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private RegularPolygonPanel polyPanel;
        private JLabel label;

        public TestPane() {
            polyPanel = new RegularPolygonPanel();
            polyPanel.addMouseMotionListener(new MouseAdapter() {
                @Override
                public void mouseMoved(MouseEvent e) {
                    if (polyPanel.isWithinPolygon(e.getPoint())) {
                        label.setText("Is inside");
                    } else {
                        label.setText("Is outside");
                    }
                }
            });
            label = new JLabel("...");
            setLayout(new BorderLayout());
            add(polyPanel);
            add(label, BorderLayout.SOUTH);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

    }

    class RegularPolygonPanel extends JPanel {

        private Polygon polygon;

        public RegularPolygonPanel() {
            //Create a Polygon object
            polygon = new Polygon();

            polygon.addPoint(40, 20);
            polygon.addPoint(70, 40);
            polygon.addPoint(60, 80);
            polygon.addPoint(45, 45);
            polygon.addPoint(20, 60);
        }

        public boolean isWithinPolygon(Point p) {
            return polygon.contains(p);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            //Draw the polygon
            g.drawPolygon(polygon);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }
    }
}

如何根据光标位置使帧中的文本更改？

1 个答案: