IndexOutOfBounds使用摆动gui跟踪鼠标

Question

当鼠标离开跟踪区域（白色JPanel）时，我不明白为什么我编写的这个简单程序在尝试更新鼠标坐标时会出现IndexOutOfBounds异常。我原以为38号线的支票会搞定的。有什么建议吗？谢谢

import java.awt.*;
import javax.swing.JFrame;
public class MainFrame extends JFrame {
    private static final long serialVersionUID = 1L;
    Label coorLabel;
    Panel coorPanel, content;
    public MainFrame(String s){
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container cont = getContentPane();
        coorLabel = new Label("Mouse Coordinates: ");
        coorPanel = new Panel();
        coorPanel.setPreferredSize(new Dimension(400,400));
        coorPanel.setBackground(Color.WHITE);
        /**
        content = new Panel();
        content.add(coorPanel, BorderLayout.PAGE_START);
        content.add(coorLabel, BorderLayout.PAGE_END);
        **/
        cont.add(coorPanel, BorderLayout.PAGE_START);
        cont.add(coorLabel, BorderLayout.PAGE_END);
        pack();
        setVisible(true);
    }
    public void updateCoor(){
        if(coorPanel.getMousePosition()!=null){
            coorLabel.setText("Mouse Coordinates: "+getMousePosition().x+", "+getMousePosition().y);
            coorLabel.repaint();
        }
    }
    public static void main(String[]args){
        MainFrame frame = new MainFrame("Coor App");
        while(true){
            frame.updateCoor();
        }
    }
}

Answer 1

看看Swing教程中的并发。您完全占用了初始具有while(true)循环的线程，并在事件调度线程之外更新用户界面。

请参阅事件监听器简介以熟悉Swing事件模型，以及如何编写鼠标运动监听器，特别是鼠标运动监听器示例。

Answer 2

以下是您应该做的：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.*;
public class Stack extends JFrame implements MouseMotionListener{
    int x;
    int y;
    JPanel p = new JPanel();
    JPanel detectPanel = new JPanel();
    JTextField t = new JTextField(10);
    JLabel l = new JLabel("Position's inside of bordered panel: ");
    public Stack(){
        setLayout(new BorderLayout());
        t.setEditable(false);
        p.add(l);
        p.add(t);
        detectPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        add(p,BorderLayout.NORTH);
        add(detectPanel,BorderLayout.CENTER);
        detectPanel.addMouseMotionListener(this);
    }
    public static void main(String[] a){
        SwingUtilities.invokeLater(new Runnable(){
            public void run(){
                Stack s = new Stack();
                s.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                s.setLocationByPlatform(true);
                s.setPreferredSize(new Dimension(640,480));
                s.pack();
                s.setVisible(true);
            }
        });
    }
    public void mouseDragged(MouseEvent e) {
    }
    public void mouseMoved(MouseEvent e) {
        x= e.getX();
        y= e.getY();
        t.setText(x+", "+y);
    }
}

Answer 3

检查coorPanel.getMousePosition()是否为空，然后引用（this）getMouseLocation()；尝试将其更改为只在检查中显示getMousePosition，并添加一个打印：

if( this.getMousePosition() != null ){
    System.out.println(getMousePosition());
    coorLabel.setText("Mouse Coordinates: "+getMousePosition().x+", "+getMousePosition().y);
    coorLabel.repaint();
}